Carbon sequestration potential and its main drivers in soils under alfalfa (Medicago sativa L.)

As a perennial forage crop, alfalfa (Medicago sativa L.) has been extensively utilized for the vegetation restoration of degraded soil and provides feedstock for forage. Its high usage can be attributed to its high yield potential and the increasing soil organic carbon (SOC) sequestration of alfalfa cultivation. However, the impact of land conversion to alfalfa on SOC content and its underlying drivers remain unclear. We performed a meta-analysis at the global scale to explore the quantified effects of alfalfa cultivation on SOC content and identify its controlling factors. We employed 1699 pairwise data points from 90 publications based on cropland/abandoned land conversion to alfalfa. Globally, cropland (cropland-alfalfa) and abandoned land (abandoned land-alfalfa) conversion to alfalfa enhanced SOC content by 12.1 % and 13.7 %, respectively. Alfalfa exhibited greater SOC content benefits in the surface soils (0-20 cm) with a lower level of initial SOC (<16 g kg-1), regardless of the land conversion type. Cropland-alfalfa was observed to increase SOC content with fertilization, irrigation, and conventional tillage in the long term (>5 years). Furthermore, abandoned land-alfalfa enhanced SOC content in the absence of alfalfa biomass removal and for longer cultivation durations (>5 years). Boosted regression tree analyses indicated variations in soil properties (75 % for cropland-alfalfa and 65 % for abandoned land-alfalfa) as the primary factors driving changes in SOC content. The dominant drivers were determined as the soil layer (51.6 %), cultivation duration (13.1 %), and initial SOC (12.9 %) for cropland-alfalfa, and initial SOC (43.7 %), soil layer (24.6 %) and cultivation duration (17.1 %) for abandoned land-alfalfa. Land conversion to alfalfa has great potential for SOC sequestration, particularly in low-fertility soils. Therefore, alfalfa cultivation is highly recommended for degraded lands due to its SOC sequestration benefits in vegetation restoration.

High levels of soil calcium and clay facilitate the recovery and stability of organic carbon: Insights from different land uses in the karst of China

Soil organic carbon (SOC) is a crucial medium of the global carbon cycle and is profoundly affected by multiple factors, such as climate and management practices. However, interactions between different SOC fractions and land-use change have remained largely unexplored in karst ecosystems with widespread rock outcrops. Owing to the inherent heterogeneity and divergent response of SOC to land-use change, soil samples with close depth were collected from four typical land-use types (cropland, grassland, shrubland, and forestland) in the karst rocky desertification area of China. The aim of this study was to explore the responses of SOC dynamics to land-use types and underlying mechanism. The results showed that land-use type significantly affected SOC contents and its fractions. Compared with cropland, the other three land uses increased the total organic carbon (TOC), microbial biomass carbon (MBC), and non-labile organic carbon (NLOC) contents by 6.11-129.44%, 32.58-173.73%, and 90.98-347.00%, respectively; this demonstrated that a decrease in both labile and recalcitrant carbon resulted in SOC depletion under agricultural land use. Readily oxidized organic carbon (ROC) ranged from 42 to 69%, accounting for almost half of the TOC in the 0-40-cm soil layer. Cropland soil showed significantly higher ROC:TOC ratios than other land-use types. These results indicated that long-term vegetation restoration decreased SOC activity and improved SOC stability. Greater levels of soil exchangeable calcium (ECa) and clay contents were likely responsible for higher stabilization and then accumulation of SOC after vegetation restoration. The carbon pool index (CPI) rather than the carbon pool management index (CPMI) exhibited consistent variation trend with soil TOC contents among land-use types. Thus, further study is needed to validate the CPMI in evaluating land use effects on soil quality in karst ecosystems. Our findings suggest that land-use patterns characterized by grass or forest could be an effective approach for SOC-sequestration potential and ensure the sustainable use of soil resources in the karst area.

Leaf carbon chemistry effectively manipulated soil microbial profiles and induced metabolic adjustments under different revegetation types in the loess Plateau, China

Microorganisms are essential components of underground life systems and drive elemental cycling between plants and soil. Yet, in the ecologically fragile Loess Plateau, scant attention has been paid to the response of microbial communities to organic carbon (C) chemistry of both leaves and soils under different revegetation conditions, as well as subsequent alternation in their C metabolic functions. Here, Fourier transform infrared (FTIR) spectrum, amplicon sequencing of 16S rRNA and ITS, and temporal incubation with Biolog-Eco 96 plates were combined to explore the vegetative heterogeneity of microbial community properties and metabolic functions, as well as their regulatory mechanisms in three typical revegetation types including Robinia pseudoacacia L. (RF), Caragana korshinskii KOM. (SL), and abandoned grassland (AG). We observed higher bacterial-to-fungal ratios (B: F = 270.18) and richer copiotrophic bacteria (Proteobacteria = 33.08%) in RF soil than those in AG soil, suggesting that microbes were dominated by r-strategists in soil under RF treatment, which is mainly related to long-term priming of highly bioavailable leaf C (higher proportion of aromatic and hydrophilic functional groups and lower hydrophobicity). Conversely, microbial taxa in AG soil, which was characterized by higher leaf organic C hydrophobicity (1.39), were dominated by relatively more abundant fungi (lower B: F ratio = 149.49) and oligotrophic bacteria (Actinobacteria = 29.30%). The co-occurrence network analysis showed that microbial interactive associations in RF and AG soil were more complex and connective than in SL soil. Furthermore, Biolog-Eco plate experiments revealed that microorganisms tended to utilize labile C compounds (carbohydrates and amino acids) in RF soil and resistant C compounds (polymers) in AG soil, which were consistent with the substrate adaptation strategies of predominant microbial trophic groups in different revegetation environments. Meanwhile, we observed greater microbial metabolic activity and diversity advantages in RF vegetation. Collectively, we suggest that besides the nutrient variables in the leaf-soil system, the long-term regulation of the microbial community by the C chemistry of the leaf sequentially alters the microbial metabolic profiles in a domino-like manner. RF afforestation is more conducive to restoring soil microbial fertility (including microbial abundance, diversity, interactive association, and metabolic capacity). Our study potentially paves the way for achieving well-managed soil health and accurate prediction of C pool dynamics in areas undergoing ecological restoration of the Loess Plateau.

Assessment of carbon sequestration potential of mining areas under ecological restoration in China

Mining activities aggravate the ecological degradation and emission of greenhouse gases throughout the world, thereby affecting the global climate and posing a serious threat to the ecological safety. Vegetation restoration is considered to be an effective and sustainable strategy to improve the post-mining soil quality and functions. However, we still have a limited knowledge of the impact of vegetation restoration on carbon sequestration potential in mining areas. In this pursuit, the present study was envisaged to integrate the findings from studies on soil organic carbon (SOC) sequestration in mining areas under vegetation restoration with field monitoring data. The carbon sequestration potential under vegetation restoration in China's mining areas was estimated by using a machine learning model. The results showed that (1) Vegetation restoration exhibited a consistently positive impact on the changes in the SOC reserves. The carbon sequestration potential was the highest in mixed forests, followed by broad-leaved forests, coniferous forests, grassland, shrubland, and farmland; (2) The number of years of vegetation restoration and mean annual precipitation were found to be the important moderating variables affecting the SOC reserves in reclaimed soils in mining areas; (3) There were significant differences in the SOC sequestration potential under different vegetation restoration scenarios in mining areas in China. The SOC sequestration potential reached up to 9.86 million t C a-1, when the soil was restored to the initial state. Based on the meta-analysis, the maximal attainable SOC sequestration potential was found to be 4.26 million t C a-1. The SOC sequestration potential reached the highest level of 12.86 million t C a-1, when the optimal vegetation type in a given climate was restored. The results indicated the importance of vegetation restoration for improving the soil sequestration potential in mining areas. The time lag in carbon sequestration potential for different vegetation types in mining areas was also revealed. Our findings can assist the development of ecological restoration regimens in mining areas to mitigate the global climate change.

An extended time-varying Budyko framework for quantifying the hydrological effect of vegetation restoration under climate variations at watershed scale

The Budyko framework, widely used to quantify the watershed hydrological response to the watershed characteristics and climate variabilities, is continuously refined to overcome the disadvantages of steady state assumption. However, dynamic variations in vegetations and climate variables are not fully integrated including coverages and precipitation regimes of intensity, frequency, and duration. To address this, we developed an innovative approach for determining the parameter ω in the Budyko framework to quantify the hydrological effects of vegetation restoration in a mesoscale watershed located in northern China. We found that fractional vegetation coverage (FVC), heavy precipitation amount (95pTOT), and the number of precipitation days (R01mm) are significant variables for estimating ω to improve the predictive capability of the watershed response. This extended time-varying Budyko framework can rigorously capture the temporal variations and underlying mechanisms of interactions between vegetation dynamic and precipitation regime partitioning precipitation (P) to R. Under the Budyko-Fu framework, compared to constant ω (ω‾) or ω that only considers FVC (ωP) or precipitation regimes (ωFVC) for simulating R, using ω that integrated FVC and precipitation regimes (ωP-FVC) can improve Nash-Sutcliffe efficiency coefficient (NSE) by 24.81%, while reduced the root mean squared error (RMSE) and relative error (RE) by 64.08% and 65.77%, respectively. Although the increase in climatic dryness (PET/P) resulted in decreased R, the increase in FVC has also a significant contribution to this decrease due to vegetation restoration. We highlight that decrease precipitation intensity (95pTOT) and frequency (R01mm) amplified the hydrological effects of vegetation restoration, causing a 79.09∼100.31% increase in R compared to the independent impact of changes in FVC. We conclude that the extended time-varying Budyko framework by precipitation regime is more rigorous for quantifying the hydrological effects of ecological restoration under climate change and providing more reliable approach for adaptive watershed management.

Microbial diversity and keystone species drive soil nutrient cycling and multifunctionality following mangrove restoration

Vegetation restoration exerts transformative effects on nutrient cycling, microbial communities, and ecosystem functions. While extensive research has been conducted on the significance of mangroves and their restoration efforts, the effectiveness of mangrove restoration in enhancing soil multifunctionality in degraded coastal wetlands remains unclear. Herein, we carried out a field experiment to explore the impacts of mangrove restoration and its chronosequence on soil microbial communities, keystone species, and soil multifunctionality, using unrestored aquaculture ponds as controls. The results revealed that mangrove restoration enhanced soil multifunctionality, with these positive effects progressively amplifying over the restoration chronosequence. Furthermore, mangrove restoration led to a substantial increase in microbial diversity and a reshaping of microbial community composition, increasing the relative abundance of dominant phyla such as Nitrospirae, Deferribacteres, and Fusobacteria. Soil multifunctionality exhibited positive correlations with microbial diversity, suggesting a link between variations in microbial diversity and soil multifunctionality. Metagenomic screening demonstrated that mangrove restoration resulted in a simultaneous increase in the abundance of nitrogen (N) related genes, such as N fixation (nirD/H/K), nitrification (pmoA-amoA/B/C), and denitrification (nirK, norB/C, narG/H, napA/B), as well as phosphorus (P)-related genes, including organic P mineralization (phnX/W, phoA/D/G, phnJ/N/P), inorganic P solubilization (gcd, ppx-gppA), and transporters (phnC/D/E, pstA/B/C/S)). The relationship between the abundance of keystone species (such as phnC/D/E) and restoration-induced changes in soil multifunctionality indicates that mangrove restoration enhances soil multifunctionality through an increase in the abundance of keystone species associated with N and P cycles. Additionally, it was observed that changes in microbial community and multifunctionality were largely associated with shifts in soil salinity. These findings demonstrate that mangrove restoration positively influences soil multifunctionality and shapes nutrient dynamics, microbial communities, and overall ecosystem resilience. As global efforts continue to focus on ecosystem restoration, understanding the complexity of mangrove-soil interactions is critical for effective nutrient management and mangrove conservation.

Temperate grassland vegetation restoration influenced by grazing exclusion and climate change

Grasslands are one of the most important terrestrial biomes, supporting a wide range of ecological functions and services. Grassland degradation due to overgrazing is a severe issue worldwide, especially in developing regions. However, observations from multiple sources have shown that temperate grasslands in China have significantly increased during the past two decades. It remains controversial what factors have driven the vegetation restoration in this region. In this study, we combined remote-sensing images and field survey datasets to quantify the contributions of different factors to vegetation restoration in six temperate grasslands in northern China. Across the six grasslands, the Normalized Difference Vegetation Index (NDVI) increased by 0.003-0.0319 year-1. The average contributions of grazing exclusion and climate change to the NDVI increase were 49.23 % and 50.77 %, respectively. Precipitation change was the primary climate factor driving vegetation restoration, contributing 50.76 % to the NDVI variance. By contrast, climate warming tended to slow vegetation restoration, and atmospheric CO2 concentration change contributed little to the NDVI increase in the temperate grasslands. These results emphasize the significant contributions of both climate change and human management to grassland vegetation restoration.

The soil microbial necromass carbon and the carbon pool stability drive a stronge priming effect following vegetation restoration

The priming effect stands as a critical factor influencing the balance of soil organic carbon (SOC). Following vegetation restoration, the carbon (C) pool stability in Platycladus orientalis forests (PO) varies, and the priming effect resulting from exogenous C addition also differs significantly. Here, we selected PO with restoration ages of 10, 15, and 30 years in the rocky mountainous area in northern China and conducted measurements of soil properties, microbial communities, microbial necromass C (MNC), SOC fractions, and the priming effect characteristics to explore the main influencing factors of the priming effect, especially the microbiological mechanisms. Our results showed that the ratio of mineral-associated organic C to particulate organic C increased. The characteristics of the priming effect showed the same pattern, and there was a significant positive correlation between the C pool stability and the priming effect. The diversity of the fungal communities increased with increasing vegetation restoration age, and the content and proportion of fungal necromass C (FNC) also increased synchronously, reaching the maximum value in the soil of PO that had been restored for 30 years. In addition, the soil water content and total nitrogen indirectly affected the priming effect by influencing the microbial communities. In summary, the results suggested that vegetation restoration can enhance the C pool stability by promoting an increase in soil FNC, thereby producing a positive priming effect. This can help deepen our understanding of the SOC mineralization changes induced by fresh C input following vegetation restoration and provides a theoretical basis for better explaining the C cycle between soil and atmosphere under the vegetation restoration models in the future.

Vegetation restoration improved aggregation stability and aggregated-associated carbon preservation in the karst areas of Guizhou Province, southwest China

Background

The change in the soil carbon bank is closely related to the carbon dioxide in the atmosphere, and the vegetation litter input can change the soil organic carbon content. However, due to various factors, such as soil type, climate, and plant species, the effects of vegetation restoration on the soil vary. Currently, research on aggregate-associated carbon has focused on single vegetation and soil surface layers, and the changes in soil aggregate stability and carbon sequestration under different vegetation restoration modes and in deeper soil layers remain unclear. Therefore, this study aimed to explore the differences and relationships between stability and the carbon preservation capacity (CPC) under different vegetation restoration modes and to clarify the main influencing factors of aggregate carbon preservation.

Methods

Grassland (GL), shrubland (SL), woodland (WL), and garden plots (GP) were sampled, and they were compared with farmland (FL) as the control. Soil samples of 0-40 cm were collected. The soil aggregate distribution, aggregate-associated organic carbon concentration, CPC, and stability indicators, including the mean weight diameter (MWD), fractal dimension (D), soil erodibility (K), and geometric mean diameter (GMD), were measured.

Results

The results showed that at 0-40 cm, vegetation restoration significantly increased the >2 mm aggregate proportions, aggregate stability, soil organic carbon (SOC) content, CPC, and soil erosion resistance. The >2 mm fractions of the GL and SL were at a significantly greater proportion at 0-40 cm than that of the other vegetation types but the CPC was only significantly different between 0 and 10 cm when compared with the other vegetation types (P < 0.05). The >2 mm aggregates showed a significant positive correlation with the CPC, MWD, and GMD (P < 0.01), and there was a significant negative correlation with the D and K (P < 0.05). The SOC and CPC of all the vegetation types were mainly distributed in the 0.25-2 mm and <0.25 mm aggregate fractions. The MWD, GMD, SOC, and CPC all gradually decreased with increasing soil depth. Overall, the effects of vegetation recovery on soil carbon sequestration and soil stability were related to vegetation type, aggregate particle size, and soil depth, and the GL and SL restoration patterns may be more suitable in this study area. Therefore, to improve the soil quality and the sequestration of organic carbon and reduce soil erosion, the protection of vegetation should be strengthened and the policy of returning farmland to forest should be prioritized.

Bio-accessibility and mobilization dynamics of soil vanadium during a 48-year vegetation restoration in a vanadium titano-magnetite tailings reservoir

Bio-accessibility of vanadium (V) in soils determines the effectiveness of vegetation restoration in the vanadium titano-magnetite tailings reservoirs because of persistent V toxicity, yet the variations in the bio-accessibility and mobilization of V in the soils with vegetation restoration remain elusive. Here, the bio-accessibility and mobilization of V in the soil-water interface were investigated along a 48-year vegetation restoration chronosequence in the Majiatian tailings reservoir using the diffusive gradients in thin films technique (DGT) and DGT-induced flux model. We found a low concentration of DGT-extracted V along the vegetation restoration chronosequence and the V fraction was dominated by the residual form, indicating a low V bio-accessibility in the soils. The bio-accessibility of V increased along the chronosequence because of the increased V resupply from solid phase, especially from the organic V fraction and the clay bound V. Low supply coefficient (R = 0.25) revealed a limited release of V from solid phase to soil solution. The kinetic resupply processes of V and its key regulating parameters were stage-specific during the vegetation restoration. The pool size of labile V in the soils determined the rapid V supply at the early and late stages, while the low desorption rate of V from the solid to liquid phase regulated the slow supply regime at the middle stage. The results of the present study highlight the importance of the long-term monitoring of soil V mobilization in the tailings reservoir because of the increased bio-accessibility and the dynamic supply of V during the vegetation restoration.

Analysis of soil water use by exotic and native vegetation in a semi-arid area and their associated interspecific competition

The exotic vegetation used in dryland vegetation restoration projects is characterized by its fast-growing and deep-rooted system, which enables it to expedite the restoration of ecosystem functions and enhance biodiversity. However, the interspecific relationship between exotic and native vegetation and soil water uptake in these restored ecosystems remains unclear, limiting our ability to evaluate the succession process and sustainability of restored ecosystems. In this study, stable isotope techniques and a proportional similarity index were used to investigate soil water use strategies and interspecific relationships between exotic and native vegetation. The results showed significant differences between the soil water use strategies of both exotic and native vegetation between seasons and species, where the proportions of deep soil water (30-100 cm) used by exotic shrubs (Caragana korshinskii) and exotic grass (Medicago sativa) were significantly higher than those used by the co-occurring native grass (Stipa bungeana) (p < 0.05). As soil water storage declined, exotic vegetation increased its utilization of deep soil water, whereas native grasses relied more on surface water (0-10 cm). This suggests that deep-rooted exotic vegetation has greater adaptability and access to water resources than shallow-rooted native vegetation. However, a prolonged decline in soil water storage led to increased competition for surface soil water (0-30 cm) between the exotic and native vegetation. This may increase the risk of degradation of exotic vegetation, particularly in situations with lower soil water content in the deep layers. Overall, this study highlights the variation in water-use strategies and interspecies relationships between exotic and native vegetation and their implications for ecosystem succession, which provides valuable insights for developing future vegetation restoration strategies and managing restored ecosystems.

An integrated approach to assess spatial and temporal changes in the contribution of the ecosystem to sustainable development goals over 20 years in China

Ecosystems are an important basis for promoting sustainable development goals (SDGs) through the provision of stable ecosystem services (ESs). In the past 20 years, China has implemented a series of forestry ecological development projects, resulting in the improvement of the ecological environment. In this context, changes in ESs in China may affect the contribution of ecosystems to the SDGs, but there is a lack of research in this area. Studies have shown that ESs can support multiple SDGs, and quantifying the contribution of ecosystems to SDGs is currently a research focus. However, few studies have quantified the extent of the contribution of different ESs to the SDGs, although these differences are generally assumed. To narrow this knowledge gap, we construct an assessment approach that integrates the extent of the contribution of different ESs to the SDGs and assesses the temporal and spatial dynamics of the contribution of ESs to the SDGs in China from 2000 to 2020. Our analysis results indicate that during the study period, fractional vegetation cover improved in China. In general, water provision, soil conservation, and food provision services improved, while carbon storage and biodiversity maintenance services declined. The contribution capacity of provincial ecosystems to the SDGs increased, except in Tibet, between 2000 and 2020. Overall, the contributions to the SDGs had obvious spatial differences. The research results can support policy formulation and research on ES management and SDGs.

Natural restoration exhibits better soil bacterial network complexity and stability than artificial restoration on the Loess Plateau, China

Natural restoration (NR, e.g., secondary succession) and artificial restoration (AR, e.g., afforestation) are key approaches for rehabilitating degraded land; however, a comparative assessment of microbial network between these approaches is lacking. We compared bacterial networks under NR and AR in two different watersheds on the Loess Plateau. Our findings revealed significantly heightened network complexity under NR compared to AR, including metrics such as node, edge, modularity, degree, centrality, and keystone nodes. NR's network robustness exceeded AR by 19.45-35.9% and 7.79-17.74% in the two watersheds, aligning with the ecological principle that complexity begets stability. The significantly higher negative/positive cohesion and natural connectivity under NR also support its better network stability than AR. Integrated analysis of paired sequencing data from five Loess Plateau studies conducted on the Loess Plateau further confirmed the higher complexity and stability of bacterial networks under NR. Further analysis unveiled "biological interactions" as primary drivers of bacterial co-occurrence (on average 84.21% of links), surpassing the influence of environmental filtering (5.17%) or dispersal limitation (4.2%). Importantly, networked communities under NR exhibited generally stronger linkages with various ecosystem function than AR. Overall, our study provides insights into vegetation restoration strategies from the perspective of microbial network, underscoring natural regeneration's potential as a superior remedy for degraded-land restoration.

Changes in soil organic carbon and nitrogen stocks following revegetation in a semi-arid grassland of North China

Long-term restoration practices have been often reported to enhance soil organic carbon (SOC) and nitrogen (N) stocks in grassland ecosystems. However, there is a limited understanding of how vegetation restoration affects SOC and N stocks at different soil depths over short timescales in semi-arid grassland of North China. To address this problem, we conducted a field study to investigate the effects of plant properties on the SOC and N stock changes during a nine-year period of grassland restoration practices (natural recovery; shallow ploughing; harrowing) in a semi-arid grassland of North China. The results revealed that three restoration practices had a positive contribution to SOC and N stocks following nine years of recovery, however, the rates of SOC and N stock changes under mechanical disturbance were lower across the 0-60 cm soil depth when compared with the natural recovery. The biomass of litter, roots, and dominant plant species were the major factors contributing to SOC and N stock changes. Our findings from the nine-year restoration experiment suggested that short-duration natural recovery is likely to be a beneficial strategy for the restoration of both the plant community and the soil nutrients. Our findings elucidate the regulatory mechanisms of dominant plant species on SOC and N stock changes following revegetation and suggest that the overcompensatory growth of dominant species should be fully considered in grassland restoration.

Superior improvement on soil quality by Pennisetum sinese vegetation restoration in the dry-hot valley region, SW China

Vegetation restoration is a good way to improve soil quality and reduce erosion. However, the impact of vegetation restoration on soil quality in the dry-hot valley region has been overlooked for many years. This study aimed to reveal the effects of Pennisetum sinese (PS) and natural vegetation (NV) on soil quality and then to explore the feasibility of introducing PS for the vegetation restoration of the dry-hot valley region. The PS and NV restoration areas deserted land evolving from cultivated land (CL) have been established since 2011. The results showed that the soil properties were obviously improved by PS from the dry to wet seasons, except for the soil available phosphorous. The comprehensive soil quality indexes of the three typical seasons (dry, dry-wet, and wet) were determined by using nonlinear weighted additive (NLWA) based on the total dataset, significant dataset and minimum dataset (MDS). The results indicated that the comprehensive minimum dataset soil quality index (MDS-SQI) of the three typical seasons evaluate soil quality well. The soil quality of PS was significantly greater than that of CL and NV (P < 0.05), as shown by the MDS-SQI. Additionally, PS could maintain a stable soil quality in the three typical seasons, while both CL and NV had obvious fluctuations. In addition, the result of the generalized linear mode suggested that the vegetation type had the greatest impact on the soil quality (44.51 %). Comprehensively, vegetation restoration in the dry-hot valley region has a positive impact on the soil properties and quality. PS is a great candidate species for the early vegetation restoration in the dry-hot valley region. This work provides a reference for vegetation restoration and rational utilization of soil resources in degraded ecosystems in dry-hot valleys and other soil erosion areas.

Mechanistic insights into dissolved organic matter-driven protistan and bacterial community dynamics influenced by vegetation restoration

Vegetation restoration projects can not only improve water quality by absorbing and transferring pollutants and nutrients from non-vegetation sources, but also protect biodiversity by providing habitat for biological growth. However, the mechanism of the protistan and bacterial assembly processes in the vegetation restoration project were rarely explored. To address this, based on 18 S rRNA and 16 S rRNA high-throughput sequencing, we investigated the mechanism of protistan and bacterial community assembly processes, environmental conditions, and microbial interactions in the rivers with (out) vegetation restoration. The results indicated that the deterministic process dominated the protistan and bacterial community assembly (94.29% and 92.38%), influenced by biotic and abiotic factors. For biotic factors, microbial network connectivity was higher in the vegetation zone (average degree = 20.34) than in the bare zone (average degree = 11.00). For abiotic factors, the concentration of dissolved organic carbon ([DOC]) was the most important environmental factor affecting the microbial community composition. [DOC] was lower significantly in vegetation zone (18.65 ± 6.34 mg/L) than in the bare zone (28.22 ± 4.82 mg/L). In overlying water, vegetation restoration upregulated the protein-like fluorescence components (C1 and C2) by 1.26 and 1.01-folds and downregulated the terrestrial humic-like fluorescence components (C3 and C4) by 0.54 and 0.55-folds, respectively. The different DOM components guided bacteria and protists to select different interactive relationships. The protein-like DOM components led to bacterial competition, whereas the humus-like DOM components resulted in protistan competition. Finally, the structural equation model was established to explain that DOM components can affect protistan and bacterial diversity by providing substrates, facilitating microbial interactions, and promoting nutrient input. In general, our study provides insights into the responses of vegetation restored ecosystems to the dynamics and interactives in the anthropogenically influenced river and evaluates the ecological restoration performance of vegetation restoration from a molecular biology perspective.

Nitrogen and phosphorus change the early natural vegetation restoration in degraded Phaeozems of gullies

The influence of nutrients during natural vegetation restoration (NVR) in complicated landscapes and hydrologic conditions has often been debated. This study aimed to clarify how nitrogen (N) and phosphorus (P) runoff influences plant biomass and biodiversity during early restoration stages in gullies. In this study, the influence of runoff containing N, P, and N + P on the biomass and diversity of ten predominant herbaceous species was simulated in two degraded Phaeozems of gullies by under controlled conditions for two years. Increasing N in runoff increased the biomass in both low-degradation Phaeozems (LDP) and high-degradation Phaeozems (HDP), and N input could increase the competitive ability of No-Gramineae (NG) and constrain G biomass in the second year. N and P increased the biomass by increasing the species abundance and individual mass but not the diversity. N input typically decreased biodiversity, while P input influenced the dynamics of biodiversity was nonmonotonic increased or decreased. Compared with sole N input, additional P accelerated the competition of NG, restrained G mass, and decreased the total biomass in LDP, while increasing the total biomass in HDP in the first year. However, additional P input did not change the N effects on biodiversity in the first year, while high P input improved the herbaceous diversity in the second year of gullies. Generally, N in runoff was the key factor influencing NVR, especially for biomass in early NVR stages. The P dose and the ratio of N:P in the runoff were the main determinants of P mediation on the N effect on NVR.

Impacts of vegetation restoration on water resources and carbon sequestration in the mountainous area of Haihe River basin, China

The mountainous region of the Haihe River basin (MHRB) plays an important role in the water resource supply of its nearby mega-cities, including Beijing and Tianjin, and large areas of cropland. With the implementation of afforestation projects in recent decades, vegetation and carbon (C) uptake have greatly increased in the MHRB. In addition, the annual runoff has significantly declined, threatening regional water security. The trade-off relationship between water yield and C uptake in the MHRB remains unknown. This study employed a biogeochemical model (Biome-BGC) to simulate the natural vegetation dynamics and gross primary productivity (GPP) during 1982-2019 driven by climate forcing. A distributed hydrological model (geomorphology-based hydrological model, GBHM) was adopted to assess the impact of vegetation restoration on the hydrological processes. The results indicated that the leaf area index in the MHRB increased significantly (P < 0.01) during 1982-2019, which led to evapotranspiration increase and runoff (R) reduction. Under the influence of vegetation restoration, both the GPP and the water use efficiency (WUE) increased significantly in the MHRB during 2000-2019, however, the improvement of WUE decreased with the aridity index increasing. Our results showed that vegetation restoration can improve C sequestration efficiency in the MHRB and that the trade-off between water yield and C sequestration should be considered in planning ecological projects to achieve C neutrality.

Woody plants have the advantages in the phytoremediation process of manganese ore with the help of microorganisms

The serious ecological damage caused by mining activities cannot be ignored. The use of an environmentally friendly restoration method to rebuild the vegetation and soil environment in the mining area has attracted more and more attention. This paper aims to study soil quality as well as vegetation characteristics of four woody species including Pinus massoniana (P. massoniana), Broussonetia papyrifera (B. papyrifera), Koelreuteria paniculata (K. paniculata), Osmanthus fragrans (O. fragrans), and two herbaceous species including Setaria viridis (S. viridis) and Cynodon dactylon (C. dactylon). In addition, we further clarified the effects of B. papyrifera and K. paniculata on soil nutrients and microbial communities after restoration. The results showed that the vegetation restoration area had better soil quality and plant community diversity, and the woody plants restoration effect were better. Compared with slag, B. papyrifera and K. paniculata remediation could improve soil pH and mitigate heavy metal contamination in mining areas, but was not effective in enhancing Soil Organic Matter (SOM), Total Nitrogen (TN), Total Potassium (TK) and Total Phosphorus (TP). In addition, the abundance and diversity of soil bacterial communities were increased. Of all the study sites, Proteobacteria had the greatest dominance. Vegetation restoration resulted in an increase in the relative abundance of Acidobacteria, while a decrease in Actinobacteria, Cyanobacteria and Firmicutes. With the restoration of vegetation, the increase of pH, the change of TN, SOM, TK, TP and the mitigation of Manganese (Mn) pollution were the main reasons affecting the soil microbial community. This study has great significance for understanding the ecological changes in the mining area after artificially mediated vegetation restoration, including changes in soil environment, plant community and microbial community, and woody plants will be more encouraged for the restoration of manganese mining areas.

Altered microbial P cycling genes drive P availability in soil after afforestation

Soil Phosphorous (P) availability is a limiting factor for plant growth and regulates biological metabolism in plantation ecosystems. The effect of variations in soil microbial P cycling potential on the availability of soil P during succession in plantation ecosystems is unclear. In this study, a metagenomics approach was used to explore variations in the composition and diversity of microbial P genes along a 45-year recovery sequence of Robinia pseudoacacia on the Loess Plateau, as well soil properties were measured. Our results showed that the diversity of P cycling genes (inorganic P solubilization and organic P mineralization genes) increased significantly after afforestation, and the community composition showed clear differences. The gcd and ppx genes were dominant in inorganic P transformation, whereas phnM gene dominated the transformation of organic P. The abundance of genes involved in inorganic P solubilization and organic P mineralization was significantly positively correlated with P availability, particularly for phnM, gcd, ppx, and phnI genes, corresponding to the phyla Gemmatimonadetes, Acidobacteria, Bacteroidetes, and Planctomycetes. The critical drivers of the microbial main genes of soil P cycling were available P (AP) and total N (TN) in soil. Overall, these findings highlight afforestation-induced increases in microbial P cycling genes enhanced soil P availability. and help to better understand how microbial growth metabolism caused by vegetation restoration in ecologically fragile areas affects the soil P cycling.

Relationship between the roots of Hippophae rhamnoides at different stump heights and the root microenvironment in feldspathic sandstone areas

Background

To solve the withering of Hippophae rhamnoides plantation in the feldspathic sandstone areas of Inner Mongolia and to promote the regeneration, rejuvenation, and sustainability of H. rhamnoides forests.

Methods

We stumped aging H. rhamnoides trees at the ground heights of 0, 10, 15, and 20 cm (S1, S2, S3, and S4, respectively) and utilized unstumped trees as the control (CK). We then analyzed the effects of the different stump heights on the roots and the root microenvironment of H. rhamnoides and the relationship between the roots and the root microenvironment in the stumped H. rhamnoides.

Results

The root fractal features, root branching rate, root length, root soluble proteins, soil moisture content, and soil nutrients among the different treatments were ranked as S3>S2>S1>S4>CK (P < 0.05). The root topological index, root proline, and malondialdehyde among the different treatments were ranked as S3<S2<S1<S4<CK (P < 0.05). The topological indices of S1, S2, S3, S4, and CK were 0.80, 0.86, 0.89, 0.94, and 0.98, respectively, and all were near 1. This result indicated a typical fishtail-shaped branching structure. The root length and root fractal dimensions were primarily affected by the positive correlation of the soil moisture content and the soil organic matter, and the root topological index was primarily affected by the negative correlation of the root proline. Root nutrients were dominant in the changes in the root architecture, while soil moisture and nutrients played supporting roles. These results indicated that stumping can promote plant root growth and root nutrient accumulation, thereby improving soil moisture and the soil nutrient distribution, and the S3 treatment had the greatest impact on the H. rhamnoides roots and root microenvironment. Therefore, the 15 cm stump height treatment should be implemented for withering H. rhamnoides in feldspathic sandstone areas to promote vegetation restoration.

Research on the application of a cement and soil aggregate for the ecological restoration of vegetation in artificial soil

The construction of high-speed roads has resulted in large amounts of steep and exposed cut slopes, posing more potential hazards in areas with mountains and hills. Vegetation restoration is an effective and environmentally-friendly way to restore exposed slopes using outside soil spray seeding, though it is difficult to establish a vegetation cover. Spraying artificial soil on high and steep slopes is a challenging task as it is difficult to keep the fluid mixture on sloped surfaces. Because of these challenges, this study applied different combinations of cement and soil aggregates in artificial soil, measuring final soil properties after one growing season. Experimental results showed that there were substantial differences in all basic soil parameters and in the soil quality index after different treatments. In particular, adding 5-10% cement content could improve the adhesion of artificial soil without remarkably reducing soil quality; adding 0.09% of soil aggregate was also beneficial to soil nutrient availability. These findings indicate that the combination of cement and soil aggregates could be applied in artificial soils for the ecological restoration of steep slope vegetation. Adding cement to the soil increased the alkaline levels of the soil, so it is important to reduce artificial soil pH in the future. The application of a cement and soil aggregate should be considered in the field for the ecological restoration of slope vegetation, and the impact of this addition on slope stability and vegetation growth should be explored with further research.

Effects of vegetation restoration on distribution characteristics of heavy metals in soil in Karst plateau area of Guizhou

In southwest China, vegetation restoration is widely used in karst rocky desertification control projects. This technology can effectively fix the easily lost soil, gradually restore the plant community and improve soil fertility. However, the change law of soil heavy metals in the restoration process remains to be further studied. Therefore, in this work, Guizhou Caohai Nature Reserve as a typical karst area was taken as the research object to investigate the influence of vegetation restoration technology on repairing soil heavy metal pollution. The spatial distribution characteristics of soil heavy metals (chromium, nickel, arsenic, zinc, lead) before and after vegetation restoration in karst area were studied by comparative analysis and linear stepwise regression analysis. The main influencing factors and spatial distribution characteristics of heavy metals in karst area were further discussed. The results showed that: (1) heavy metals in karst soils are affected by surface vegetation, root exudates, microorganisms and leaching. Only heavy metals nickel (Ni) and lead (Pb) showed the tendency of surface enrichment and bottom precipitation enrichment in non-karst soils. Path analysis suggested that non-metallic soil factors such as soil bulk density (BD), total nitrogen (TN) and ammonium nitrogen (NH₄ ⁺-N) had direct effect on the content of heavy metals in soil. (2) The proportion of 0.25-2 mm aggregates in the surface soil of vegetation restoration belt was more than 40%, and the proportion of surface soil ≤2 mm aggregates in this increased to 83% and 88%, respectively, which could improve the soil structure and properties effectively. (3) Vegetation restoration effectively restored the nutrient elements such as carbon and nitrogen in the soil, and enhanced the soil material circulation. Furthermore the content of heavy metals in the surface soil higher than that in the 10-20 cm soil layer. Plant absorption, biosorption mechanism of microorganisms, coupling of root exudates, dissolution of soil soluble organic carbon and pH make the contents of heavy metals Cr, Ni and Pb in vegetation restoration belt slightly lower than those in karst soil. At the same time, affected by vegetation coverage, residual heavy metals in soil are further leached by surface runoff. Therefore, the content of heavy metals in soil could reduce combined heavy metal enrichment plants for extraction with remediation. This study elucidates the advantages and remedy mechanism of vegetation restoration in the remediation of heavy metal contaminated soils in Caohai area of Guizhou, and this plant activation and enrichment extraction remediation technology would be popularized and applied in the remediation of heavy metal contaminated soils in other karst areas.

Ecological function-oriented vegetation protection and restoration strategies in China's Loess Plateau

Potential natural vegetation (PNV) can provide a reference for vegetation protection and restoration. Previous studies often used PNV patterns as a reference; however, they ignored PNV ecological functions, impeding the establishment of function-oriented vegetation protection and restoration plans. To address this issue, this study used Loess Plateau of China as a case study to propose an ecological function-oriented vegetation protection and restoration framework based on PNV patterns and ecological functions. The results showed that PNV patterns, ecological functions, and their synergistic and trade-off relationships represented distinct spatial differences that would be largely influenced by climate change. This suggested that vegetation protection and restoration should be adapted to climate change. The protection and potential restoration regions for actual forest and grass were detected based on the stable PNV regions. Approximately 34.5%-41.4% of actual forest and 81.2%-82.3% of actual grass should be protected. Further, 13.9%-16.2% of actual forest and 14.7%-15.2% of actual grass have the potential to be restored to grass and forest, respectively, and lastly, the priority regions of forest and grass protection and potential restoration were determined according to a composite ecological functions index. Moreover, forest protection should be prioritized, followed by forest potential restoration, grass potential restoration, and grass protection. These results would be conducive to forest and grass protection and restoration of the Loess Plateau. The proposed framework is applicable to other regions of the world for developing vegetation protection and restoration strategies.

Soil properties under different ecological restoration modes for the quarry in Yanshan mountains of Hebei province, China

The ecological environment of quarry mining area is fragile, and the vegetation restoration cycle is long and difficult, so scientific and appropriate artificial vegetation is of great significance to ecological restoration. The purpose of this study was to evaluate the herbaceous and woody vegetation restoration, including Medicago sativa (Me), artificial miscellaneous grass (Mg), Rhus typhina (Rh), fruit orchard (Or) and Pinus tabulaeformis (Pi), to investigate the soil physicochemical properties and the structure of the microbial communities, and to reveal the correlation between them. The results addressed that Medicago sativa and artificial miscellaneous grass had significant effect on soil remediation, which were conducive to scientific and efficient ecological restoration, and could promote ecological restoration in the damaged ecosystems. While, the modes of Rh and Pi were not suitable for ecological restoration in this study area because they had strong allelopathy. Another arborous restoration mode of Or showed a better improvement effect (including soil nutrients, soil microbial diversity, etc.) than that of Rh and Pi. The findings also indicated that the herbaceous vegetation restoration modes of Me and Mg significantly increased the relative abundance of Proteobacteria, Acidobacteria, Actinobacteria bacteria, Ascomycota and Mortierllomycota fungi, and reduced the relative abundance of Firmicutes bacteria and Basidiomycota fungi. This study also revealed that the trend of bacterial localization in the fruit orchard, artificial miscellaneous grass and Medicago sativa was more obvious. Among many soil abiotic factors, the contents of organic matter, available nitrogen and pH were the most important factors affecting soil microbial community.

An ecological remediation model combining optimal substrate amelioration and native hyperaccumulator colonization in non-ferrous metal tailings pond

The vegetation deterioration and pollution expansion from non-ferrous metal tailings pond have been found in many countries leading to water soil erosion and human health risk. Conventional ecological remediation technologies of mine tailings such as capping were costly and elusive. This study provided an economic and effective model as an alternative by substrate amelioration and vegetation restoration. A field experiment was carried out on a silver tailings pond in southwest China. Tailings substrate was ameliorated by adding organic matter (decomposed chicken manure, DCM), structural conditioner (polyacrylamide, PAM), water-retaining agent (acrylic acid-bentonite water-retaining agent, AAB), and heavy metal immobilizer (biofuel ash, BFA), which were optimized by laboratory experiment. Native heavy metal hyperaccumulator, Bidens pilosa, was colonized. Vegetation coverage and plant height of Bidens pilosa reached about 80% and over 30 cm respectively after 3 months, and the turbidity of tailings leaching solution decreased by 60%. The practice showed that the proportion of available heavy metals in tailings substrate was significantly lower than that in the soil surrounding mining area. Immobilization didn't have stabilization effect on Cd, Zn, and Pb, and As was only 0.002%, phytoremediation had stabilization effect of Cd, Zn, As, and Pb were 2.5-3.5%, 1-2%, 0.25-0.5%, and 0.25-0.75%. Phytoremediation was more effective significantly in controlling heavy metal pollution risk of tailings than immobilization. These results provided a new ecological remediation OSA-NHC model, meaning a combination of optimal substrate amelioration and native hyperaccumulator colonization, which could achieve vegetation restoration and augment heavy metal pollution control in non-ferrous metal tailings pond.

Response of spatio-temporal changes in sediment phosphorus fractions to vegetation restoration in the degraded river-lake ecotone

Phosphorus (P) is an essential element in the ecosystem and the cause of the eutrophication of rivers and lakes. The river-lake ecotone is the ecological buffer zone between rivers and lakes, which can transfer energy and material between terrestrial and aquatic ecosystems. Vegetation restoration of degraded river-lake ecotone can improve the interception capacity of P pollution. However, the effects of different vegetation restoration types on sediment P cycling and its mechanism remain unclear. Therefore, we seasonally measured the P fractions and physicochemical properties of sediments from different restored vegetation (three native species and one invasive species). The results found that vegetation restoration significantly increased the sediment total P and bioavailable P content, which increased the sediment tolerance to P pollution in river-lake ecotone. In addition, the total P content in sediments was highest in summer and autumn, but lower in spring and winter. The total P and bioavailable P contents in surface sediments were the highest. They decreased with increasing depth, suggesting that sediment P assimilation by vegetation restoration and the resulting litter leads to redistribution of P in different seasons and sediment depths. Microbial biomass-P (MBP), total nitrogen (TN), and sediment organic matter (SOM) are the main factors affecting the change of sediment phosphorus fractions. All four plants' maximum biomass and P storage appeared in the autumn. Although the biomass and P storage of the invasive species Alternanthera philoxeroides were lower, the higher bioavailable P content and MBP values of the surface sediments indicated the utilization efficiency of sediment resources. These results suggest that vegetation restoration affects the distribution and circulation of P in river and lake ecosystems, which further enhances the ecological function of the river-lake ecotone and prevents the eutrophication and erosion of water and sediment in the river-lake ecotone.

Vegetation restoration facilitates belowground microbial network complexity and recalcitrant soil organic carbon storage in southwest China karst region

Soil organic carbon (SOC) is an important component of soil ecosystems, and soils are a hotbed of microorganisms playing critical roles in soil functions and ecosystem services. Understanding the interaction between SOC and soil microbial community is of paramount significance in predicting the C fate in soils following vegetation restoration. In this study, high-throughput sequencing of 16S rRNA and ITS genes combined with ¹³C NMR spectroscopy analysis were applied to characterize SOC chemical compounds and elucidate associated soil microbial community. Our results indicated that the contents of SOC, total nitrogen, total phosphorus, microbial biomass carbon and biomass nitrogen, dissolved organic carbon, available potassium, exchangeable calcium and soil moisture increased significantly (P < 0.05) along with the vegetation restoration processes from corn land, grassland, shrub land, to secondary and primary forests. Moreover, the Alkyl C and O-alkyl C abundance increased with vegetation recovery, but no significant differences of Alkyl C were observed in different successional stages. In contrast, the relative abundance of Methoxyl C showed an opposite trend. The dominate phyla Proteobacteria, Acidobacteria, Actinobacteria, Ascomycota and Basidiomycota were strongly related to SOC. And, SOC was found to be the determining factor shaping soil bacterial and fungal communities in vegetation restoration processes. The complexity of soil bacteria and fungi interactions along the vegetation restoration chronosequence increased. Determinism was the major assembly mechanism of bacterial community while stochasticity dominated the assembly of fungal community. Bryobacter, Haliangium, and MND1 were identified as keystone genera in co-occurrence network. Besides, the dominant functional groups across all vegetation restoration processes were mainly involved in soil C and N cycles and linked to the enhanced recalcitrant SOC storage. Our results provide invaluable reference to advance the understanding of microbe response to vegetation restoration processes and highlight the impact of microbes on recalcitrant SOC storage.

Quantitative analysis of vegetation restoration and potential driving factors in a typical subalpine region of the Eastern Tibet Plateau

Vegetation restoration is an essential approach to re-establish the ecological balance in subalpine areas. Changes in vegetation cover represent, to some extent, vegetation growth trends and are the consequence of a complex of different natural factors and human activities. Microtopography influences vegetation growth by affecting the amount of heat and moisture reaching the ground, a role that is more pronounced in subalpine areas. However, little research is concerned with the characteristics and dynamics of vegetation restoration in different microtopography types. The respective importance of the factors driving vegetation changes in subalpine areas is also not clear yet. We used linear regression and the Hurst exponent to analyze the trends in vegetation restoration and sustainability in different microtopography types since 2000, based on Fractional Vegetation Cover (FVC) and identified potential driving factors of vegetation change and their importance by using Geographical Detector. The results show that: (1) The FVC in the region under study has shown an up-trend since 2000, and the rate of increase is 0.26/year (P = 0.028). It would be going from improvement to degradation, continuous decrease or continuous significant decrease in 47.48% of the region, in the future. (2) The mean FVC is in the following order: lower slope (cool), lower slope, lower slope (warm), valley, upper slope (warm), upper slope, valley (narrow), upper slope (cool), cliff, mountain/divide, peak/ridge (warm), peak/ridge, peak/ridge (cool). The lower slope is the microtopographic type with the best vegetation cover, and ridge peak is the most difficult to be afforested. (3) The main factors affecting vegetation restoration in subalpine areas are aspect, microtopographic type, and soil taxonomy great groups. The interaction between multiple factors has a much stronger effect on vegetation cover than single factors, with the effect of temperatures and aspects having the most significant impact on the vegetation cover changes. Natural factors have a greater impact on vegetation restoration than human factors in the study area. The results of this research can contribute a better understanding of the influence of different drivers on the change of vegetation cover, and provide appropriate references and recommendations for vegetation restoration and sustainable development in typical logging areas in subalpine areas.

Different biomass production and soil water patterns between natural and artificial vegetation along an environmental gradient on the Loess Plateau

Loess Plateau (LP) is a vulnerable and climate-sensitive ecoregion. With the implementation of "Grain for Green" project (GGP), the vegetation cover has largely improved, while the contradiction between overconsumption of soil water and sustainability of restored vegetation is increasingly prominent, and further threatening the ecosystem sustainability and socioeconomic development. Understanding the different responses of relations of biomass production and soil water regimes between natural and artificial vegetation along environmental gradient will be crucial for sustainability of restored vegetation on the LP. Here, aboveground biomass (AGB) and soil water content (SWC) of natural and artificial vegetation were measured in steppe, forest-steppe and forest zone from 2008 to 2017 on the Yanhe River catchment. The results showed that artificial vegetation consumed more soil water than natural vegetation in steppe and forest-steppe zone, while it did not over consume soil water in forest zone. The AGB of natural vegetation in forest zone was significantly higher than that in steppe and forest-steppe zone. Steppe zone had serious overload of artificial vegetation (overload ratio: 5.35), while no overload occurred in forest zone. So, we suggest a cessation of artificial vegetation expansion in steppe zone. In steppe zone, planting artificial vegetation increased competition intensity between AGB and SWC, and the relative benefit tended to be AGB, their competition intensity was the highest. In forest zone, the trade-off relationship between AGB and SWC had no significant difference between natural and artificial vegetation, and the competition intensity between the AGB and SWC was the weakest. Optimal vegetation restoration approach would maintain the balance between vegetation restoration and soil water. To obtain social and ecological sustainability on the LP, vegetation suitability and suitable management along different environmental gradients should be considered and identified in the future revegetation project.

Driving factors of ecosystem services and their spatiotemporal change assessment based on land use types in the Loess Plateau

A clear understanding of the driving factors for different ecosystem services (ESs) is quite essential for sustainable ecosystem management. It is important to strengthen research in ESs and social sustainable development to identify the main driving factors of different ESs. This study assessed carbon sequestration (CS), water yield (WY) and soil conservation (SC) from 2000 to 2018 in the Loess Plateau using CASA (The Carnegie-AmesStanford Approach), InVEST (Integrated Valuation of Ecosystem Services and Trade-offs) and RUSLE (Revised Universal Soil Loss Equation) models. The spatial heterogeneity, trade-offs and synergies and driving factors were explored in the whole Loess Plateau. The results showed that the WY, CS and SC had increased from 2000 to 2018. The spatial relationships between WY and SC, SC and CS, and WY and CS were mainly synergistic. Annual mean precipitation (MAP) was the dominant driving factor of WY, while normalized difference vegetation index (NDVI) and slope (SL) had the strongest explanatory power for CS and SC. The LU was the most critical factor affecting the ESs in the different climatic zones. These results could act as a reference for decision-makers on how to control various influencing factors of ESs to improve the local ecology under local conditions.

Revegetation of coal mine degraded arid areas: The role of a native woody species under optimum water and nutrient resources

Ecological restoration of coal mine degraded soils across arid and semi-arid environments worldwide remains particularly challenging. We used a combination of greenhouse and field experiments to assess the potential role of a woody species, Ulmus pumila, in the restoration of degraded soils associated with coal-mining activities in the northwest China. We investigated how various combinations of water-nitrogen-phosphorus (W-N-P) resources affect multiple growth parameters in U. pumila. We found that several plant growth traits significantly improved with W-N applications, regardless of P inputs. Moderate-to-highest W-N-P doses increased net photosynthesis and transpiration rates, water use efficiency, stomatal conductance, chlorophyll and carotenoid contents under greenhouse conditions. A combination of high W together with low N-P applications led to high relative water content and net photosynthetic rates under field conditions. Increasing of N-P doses under W-shortage condition, aided U. pumila to enhance osmotic adjustments by increasing contents of proline and soluble sugar and also boost the activity of superoxide dismutase, peroxidase and catalase in leaf tissues to reduce accumulation of reactive oxygen species and malondialdehyde content in all conditions of greenhouse and field. Our study is the first to assess the optimum W-N-P resources in U. pumila and demonstrate that optimum growth performance could be obtained under W supplements corresponding to 90 mm year-1, N and P at 110 and 45 kg ha-1, respectively, under field condition. These findings can have far reaching implications for vegetation restoration of degraded areas associated with coal-mining activities across arid and semi-arid regions worldwide.

The spatiotemporal change of cropland and its impact on vegetation dynamics in the farming-pastoral ecotone of northern China

Due to the unfavorable soil conditions and water resources, the cropland use pattern in the farming-pastoral ecotone in northern China is complex. The program named "Grain for Green" has accelerated the cropland change. However, the complex cropland and retired cropland are challenging to monitor with remote sensing due to their spatially dispersed and easily confused with spectrally similar land use classes such as nature grasslands and non-cropped fields. Taking farming-pastoral ecotone in the northern foot of the Yinshan Mountains as a case study, we explored a classification approach for complex cropland and retired cropland, which was introduced as a specific land use class by using multi-temporal Landsat TM and OLI images with Google Earth Engine. During 1990-2000, cropland increased with a sharper growth and increased with a slower growth from 2001 to 2010, and then decreased significantly from 2011 to 2019, to lead the cropland area in 2019 was smaller than an area in 1990. We analyzed the spatiotemporal trajectories of retired cropland in 2019 using the Land Use Change Trajectory method to evaluate its source. In our finding, approximately 77% of retired cropland was labelled as cropland before 2019; albeit, not all retired cropland was converted from cropland. Moreover, we qualitatively assessed the vegetation dynamics in the study area by utilizing the long-term NDVI-mean value to reveal that vegetation coverage has shown a continuously increasing trend. It is related to the decline of cropland and the increase of retired cropland at the same rate. Our results highlighted that the "Grain for Green" program had led the vegetation restoration in the farming-pastoral ecotone. Our approach for monitoring cropland and retired cropland can improve the understanding of the driving factors and consequences of these critical land use change trajectories.

Effects of vegetation restoration types on soil nutrients and soil erodibility regulated by slope positions on the Loess Plateau

Soil degradation is significantly increased driven by soil nutrient loss and soil erodibility, thus, hampering the sustainable development of the ecological environment and agricultural production. Vegetation restoration has been widely adopted to prevent soil degradation given its role in improving soil nutrients and soil erodibility. However, it is unclear which vegetation type has the best improving capacity from soil nutrient and soil erodibility perspectives. This study selected three vegetation restoration types of grasslands (GL), shrublands (SL), and forestlands (FL) along the five slope positions (i.e., top, upper, middle, lower, and foot slope), to investigate the effects of vegetation restoration types on soil nutrients and soil erodibility. All vegetation restoration types were restored for 20 years from croplands (CL). We used comprehensive soil nutrient index (CSNI) and comprehensive soil erodibility index (CSEI) formed by a weighted summation method to reflect the effect of vegetation restoration on the improving capacity of soil nutrient and erodibility. The results showed the vegetation types with the highest comprehensive soil quality index (CSQI) at the top, upper, middle, lower and foot slope were FL (1.92), FL (1.98), SL (2.15), FL (2.37) and GL (3.93), respectively. When only one vegetation type was considered on the entire slope, SL (0.59) and FL (0.59) had the highest CSNI, the SL had the lowest CSEI (0.34) and the highest CSQI (1.89). The CSNI was mainly influenced by soil structure stability index (SSSI), sand content, silt + clay particles, and CSEI was controlled by soil organic matter (SOM), macroaggregates and microaggregates. Moreover, the CSQI was influenced by pH, silt and clay content, and biome coverage (BC). The study suggested the SL were advised as the best vegetation restoration type on the whole slope from improving soil nutrients and soil erodibility.

The formation of large macroaggregates induces soil organic carbon sequestration in short-term cropland restoration in a typical karst area

Cropland restoration induces litter and root inputs and promotes the development of biological soil crusts (BSCs), which may promote aggregate formation and soil organic carbon (SOC) sequestration. However, litter, roots and BSCs have not been simultaneously considered when assessing soil aggregate and aggregate-associated SOC fraction responses to cropland restoration in subtropical areas. Here, we measured particulate organic carbon (POC) and mineral-associated organic carbon (MOC) in bulk soils and soil aggregates after 15 years of cropland restoration. Soil samples of cropland (CL) and four cropland restoration types (plantation forest [PF], forage grassland [FG], mixed plantation of forest and forage grassland [FF], and abandoned natural grassland [NG]) from depths of 0-30 cm were collected. Cropland restoration significantly increased SOC and POC in bulk soil at the 0-5 cm depth. However, only in FG did SOC significantly increase at depths of 5-15 cm, and POC significantly increased at depths of 5-30 cm. The large macroaggregate (5-10 mm and 2-5 mm) proportions increased significantly at the 0-15 cm depth after cropland restoration, and FG, FF and NG also increased the 5-10 mm aggregate proportions at the 15-30 cm depth. The SOC sequestration in bulk soil with cropland restoration was attributed to increases in the aggregate-associated organic carbon (AAOC) pool in large macroaggregates, which was mainly attributed to the increased aggregate amount rather than the increased AAOC concentration in large macroaggregates. Our results also indicated that an increase in aggregate-associated particulate organic carbon (AAPOC) led to an increase in AAOC. Variation partitioning indicated that the formation of large macroaggregates was controlled by the litter-moss-root interactive effect in this karst area. FG could be a better short-term cropland restoration strategy, increasing large macroaggregates in deeper soil layers better than the other vegetation types and promoting soil carbon sequestration in deeper soil layers.

Mapping annual land disturbance and reclamation in rare-earth mining disturbance region using temporal trajectory segmentation

Rare-earth mining has caused extensive damage to soil, vegetation, and water, significantly threatening ecosystems. Monitoring environmental disturbance caused by rare-earth mining is necessary to protect the ecological environment. A spatiotemporal remote sensing monitoring method for mining to reclamation processes in a rare-earth mining area using multisource time-series satellite images is described. In this study, the normalized difference vegetation index (NDVI) is used to evaluate the mining impact. Regression analysis is conducted to relate the HJ-1B CCD and Landsat 5/8 data to reduce the NDVI error related to sensor differences between different datasets. The analysis method of NDVI trajectory data of ground objects is proposed, and areas of environmental disturbance caused by rare-earth mining are identified. Pixel-based trajectories were used to reconstruct the temporal evolution of vegetation, and a temporal trajectory segmentation method is established based on the vegetation changes in different disturbance stages. The temporal trajectory of the rare-earth disturbance points is segmented to extract features in each stage to obtain the disturbance year, recovery year, and recovery cycle and evaluate the vegetation recovery after rare-earth mining disturbance. We applied the method to a stack of 20 multitemporal images from 2000 to 2019 to analyze vegetation disturbance due to rare-earth mining and vegetation recovery in the upper reaches of the Guangdong-Hong Kong-Macao Greater Bay Area, China. The results show the following. (1) Mining industry in the study area experienced rapid expansion before 2008, but growth slowed since the policies implemented by the government since 2009 to restrict rare-earth mining. (2) The continuous influence to the land caused by rare-earth mining can last for decades; however, the reclamation activities shorten the recovery cycle of mining land from 5 to 3 years.

Determination of the optimal ecological water conveyance volume for vegetation restoration in an arid inland river basin, northwestern China

Overexploitation of water resources has led to severe ecological degradation and even desertification in some arid inland river basins, northwestern China. To alleviate or restore the degraded vegetation ecosystem, ecological water conveyance (EWC) has become an important and effective measure. Scientific assessment of the impact of EWC on vegetation restoration and determination of the corresponding optimal EWC volume (EWCV) are important to formulate rational ecological water management. In this study, long time series normalized difference vegetation index (NDVI) was used to extract the restored vegetation area in Qingtu Lake area, a terminal lake in inland Shiyang River basin, northwestern China. The relationship between restored vegetation coverage and EWC was explored to determine the optimal EWCV. The restored vegetation area (RVA) increased dramatically in the first five years and became stable from 2016. The time lag of the response of RVA increase to EWC was about 2 years. A bell-shaped function between RVA and groundwater depth was obtained based on the results from Unmanned Aerial Vehicle (UAV) and micro terrain of the lake area. Based on the fitted function, five groundwater depth thresholds were obtained. The optimal groundwater depth in the hydrometric station was 2.91 ± 0.09 m for the maximal RVA (17.08 ± 3.25 km²). A polynomial function between the yearly EWCV and groundwater depth was developed and the EWCV thresholds corresponding to the groundwater depth thresholds were estimated. The optimal EWCV into Qingtu Lake was 2224.4 × 10⁴ m³ for the maximal RVA. The correspondingly optimal EWCV from Hongyashan Reservoir was 3271.4 × 10⁴ m³. The spatial distribution patterns of remotely sensed water surface and NDVI suggested that expanding the water-receiving area of conveyed water was useful to improve the vegetation growth. This study provides a reference for assessing the impact of EWC on vegetation restoration and determining the correspondingly optimal EWCV in arid inland river basins.

The variation of rainfall runoff after vegetation restoration in upper reaches of the Yellow River by the remote sensing technology

In history, the Yellow River has been suffering from endless floods, which has brought great damage or destruction to agriculture, cities, and people's lives and property along the river. In this study, the rainfall and runoff characteristics of the Yellow River upstream (Tangnaihai and Lanzhou) after the vegetation restoration were analyzed. With the government implementation of ecological restoration policy since 1999, the vegetation cover in this area has been greatly improved and the normalized difference vegetation index (NDVI) shows a fluctuating increase, with the maximum value of 0.323 (in 2010) and the minimum value of 0.289 (in 2008). The trend of rainfall from 1948 to 2019 was increased, with an average increase of 1.747mm per 10 years. Before the implementation of ecological policy (1948 to 1999), the rainfall decreased by an average of 0.953mm per 10 years, and then increased by an average of 16.519mm per 10 years (2000 to 2019). From 1998 to 2017, the runoff increased by 11.13×10⁸m³ per 10 years (Tangnaihai) and 30.517×10⁸ m³ (Lanzhou) per 10 years, which was due to the increase in rainfall. Annual sediment discharge and annual average sediment concentration decreased by 0.002×10⁸t and 0.103 kg/m³ per 10 years in Tangnaihai, 0.081×10⁸t and 0.395kg/m³ per 10 years in Lanzhou respectively. The decreasing intensity of Lanzhou station was greater. The sediment runoff modulus of Tangnaihai and Lanzhou decreased by 1.4875 km²·year and 4.9439 km²·year respectively. The increase of vegetation has a decreasing effect on sediment discharge. The implementation of ecological restoration policy reduces the amount of sediment into the Yellow River and plays an important role in the protection of ecological environment in the Yellow River Basin.

Effects of Vegetation Restoration on Soil Enzyme Activity in Copper and Coal Mining Areas

Mining areas are suffering from serious environmental hazards, such as soil erosion, water pollution as well as land degradation. In this study, two types of mining areas in Anhui Province, China-one a copper mining area and the other a coal mining area-were selected to compare the soil properties under different vegetation restoration conditions, which can be generally classified into reclaimed and non-reclaimed areas. Soil catalase and urease activities and soil chemical properties were chosen to be the main indicators of soil quality. Principal component analysis was used to evaluate the overall soil fertility in the copper and coal mining areas. Results showed that in the copper mining area soil catalase activity was between 12.36 and 19.17 μg g^-1 h^-1 and urease activity was between 0.03 and 12.05 μg g^-1 h^-1. And in coal mining area, soil catalase activity was between 3.52 and 9.72 μg g^-1 h^-1 and urease activity was between 2.71 and 10.81 μg g^-1 h^-1. Moreover, soil catalase and urease activities in degraded areas were lower than those in reclaimed areas. Soil catalase activity and soil urease activity were significantly correlated with total potassium and total nitrogen, respectively. Soil quality in land types with vegetation restoration was higher than in non-reclaimed areas and old subsidence areas, while soil quality in the copper mining area was generally higher than in the coal mining area. Thus, the optimum measure in this region to ameliorate these degraded soils is vegetation restoration, which helps not only to improve the environment, but also to enhance soil quality in these degraded lands.

The convergence of species composition along the drawdown zone of the Three Gorges Dam Reservoir, China: implications for restoration

Many rivers across the globe are regulated by dams, resulting in a strong alteration of the plant community composition of the drawdown zone. But, how these changes happen along the drawdown zone is less understood. In this study, a multivariate analysis was used to explore plant composition and similarity along the drawdown zone of the Three Gorges Dam Reservoir (TGDR), China. The dominant plant species, species richness, indicator species, and growth form were compared among the upstream, midstream, and downstream of the TGDR. Moreover, variation partitioning was used to determine the relative importance of environmental factors and spatial factors. Results showed that only a few species contributed the most to the community composition of the study area, and there was an extreme similarity in the plant community composition across the three different river segments. Furthermore, the results of the linear regression model demonstrated a steady declining trend in species richness along the drawdown zone, with the lowest species richness in the downstream segment. In addition, variation partitioning revealed 11% and 8% of the species composition change under environmental and spatial factors, respectively. Our results suggested that the dam impoundment led to the convergence of species composition along the drawdown zone of the TGDR, and environmental filtering and dispersal limitation played an imperative role in shaping species composition. The study highlighted the importance of restoration activities in overcoming the barriers of seed dispersal and seedling establishment in the degraded drawdown zone ecosystem of the TGDR.

Identifying vegetation restoration effectiveness and driving factors on different micro-topographic types of hilly Loess Plateau: From the perspective of ecological resilience

Vegetation restoration is an important way to improve the sustainability of the ecosystem in the hilly Loess Plateau. The variation of vegetation coverage, caused by the combined effects of meteorological factors and human activities, reflects the succession trend of regional ecosystems. Given the complexity and the diversity of landform in the hilly Loess Plateau, vegetation restoration is more affected by topographic factors. Nevertheless, few studies have considered the characteristics and trends of vegetation restoration under different micro-topographic types in the long-time series. From the perspective of ecological resilience based on the fractional vegetation cover (FVC), the trend, the hurst exponent, and the geographical spatial research were used to analyze the variation and future sustainability of vegetation restoration on different micro-topographic types for 20 years. Besides, the spatial autocorrelation, principal component analysis (PCA) and geographically weighted regression (GWR) were applied to identify the driving factors of vegetation restoration. The results showed: (1) the average of the overall regional vegetation coverage was 61.32%, and only 0.95% of the regional vegetation was degraded in the past 20 years. However, in the future, 69.87% of the area would be degraded from improvement, and 0.52% would be significantly decreased; (2) the vegetation coverage in descending order was as follows: ridge area with shady and steep slope, gully area with shady and steep slope, ridge area with sunny and steep slope, gully area with sunny and steep slope, gully area with shady and gentle slope, ridge area with shady and gentle slope, ridge area with sunny and gentle slope, gully area with sunny and gentle slope, valley area; (3) the difference of vegetation degradation among micro-topography was remarkable, and the valley area and gully area with sunny and steep slope have the greatest decrease; (4) the primary factors affecting vegetation restoration in the hilly Loess Plateau were temperature, moisture, soil quality, and social economical condition, and the dominant factors were various under different micro-topographic types and villages. Therefore, it is necessary to adjust ecological engineering measures by comprehensively considering the regional differences among dominant factors of vegetation restoration.

C4 herbs dominate the reservoir flood area of the Three Gorges Reservoir

Dam operations can dramatically degenerate riparian vegetation. To improve the restoration practices of reservoir riparian vegetation, it is important to understand which and how a dominant species physiologically and ecologically maintain high fitness in this type of ecosystems. We explored the compositional change of riparian plants during the long-term flood-dry-flood cycle in the reservoir flood area (RFA) of the Three Gorges Reservoir Area (TGRA), China. In total 769 vascular plant species (belonging to 415 genera in 122 families) existed in the study area before damming (prior to 2006, i.e. the natural riparian zone). Following damming (2008-2018), plant species diversity rapidly declined, with only 51 species identified in 2018 (45 genera in 22 families). Before damming, perennial herbs, annual herbs and shrubs co-dominated the study area. After damming, the proportion of shrubs decreased significantly, and the proportion of annuals to total plants increased by 20%. Alien invasive species proportion increased from 5% to 18%. Notably, the proportion of C₄ species increased significantly from 7% to 31%. Ten of the 16 dominant species in RFA since 2015 were C₄ Poaceae species. Our study indicates that dam construction could cause severe biodiversity loss of riparian plants and draw alien species invasion. Besides, C₄ herbs would dominate the RFA. A higher photosynthetic rate could help C₄ plants grow faster to cope with the nitrogen deficiency and short growth cycles in RFA. Hence, screening C₄ herbs for vegetation restoration might aid in maintaining biodiversity and ecosystem functions in flood-dry-flood reservoir flood areas.

Spatiotemporal tradeoffs and synergies in vegetation vitality and poverty transition in rocky desertification area

Vegetation recovery and poverty alleviation are critical problems in the karst national designed poor counties (NPDC) in southwest China. However, little information is available about the relationship between poverty and vegetation dynamics in these areas. In this study, we used remote sensing and statistical datasets from 2000 to 2015 to identify the relations between vegetation dynamics and poverty among the NPDC in southwest rocky desertification areas. We estimated the vegetation dynamics using the Normalized Difference Vegetation Index and poverty with the rural per capita net income. Local indicator of spatial association and the space-time transition type of poverty were applied to identify spatial patterns of the poverty spatial distribution relationship and transition. Also, poverty, natural and ecological governance factors were assessed using the Geo-detector method to uncover the driving factors of karst vegetation. The results showed that vegetation increased significantly (p < 0.05) in karst NPDC (82.82%) and rocky desertification control counties (78.77%). The karst NPDC was significantly clustered. The hot spots of rural per capita net income changed from west and north (2000) to only north (2015) and cold spots changed from east and south (2000) to only south (2015). The rural per capita net income spatiotemporal transition was higher in 2000 than in 2015. We found a weak synergy between vegetation change and poverty type transition in 42.86% of the browning counties, 45.45% in the slowly greening counties, and 43.65% in stable greening counties. However, 57.50% of counties in the quick greening counties showed a tradeoff relationship with the poverty type transition. The rocky desertification rate and ecological engineering measures affected vegetation dynamics importantly. The results will help decision-makers to understand the interdependence between vegetation and poverty. This will contribute to better policies formulation to tackle poverty in the karst rocky desertification area.

Influence of the invasive shrub Nicotiana glauca Graham on the plant seed bank in various locations in Taif region, western of Saudi Arabia

Invasive species have been considered as one of the most serious threats to the biodiversity of various ecosystems, particularly in arid regions. The present study aimed to assess the influence of the invasive shrub Nicotiana glauca on the biodiversity of different habitats in Taif region, Saudi Arabia as well as to determine the highest habitat with seed bank of N. glauca. Soil samples were collected from three locations (Alwaht, Ash-shafa, and Ar Ruddaf), invaded with N. glauca, and analyzed for the soil seed bank. A soil seed experiment was designed in a greenhouse, whereby emerged plant seedlings were left to grow for three months and identified as well as the species density and biodiversity were assessed under and outside the canopy of N. glauca. Also, the floristic composition, life forms, and chorotype spectra of the plant species of the seed bank were analyzed. A total of 42 species, belonging to 23 families, were recorded in the soil seed bank. Asteraceae, Poaceae, and Cyperaceae were the major families (42.9%). The life form spectra of the recorded species were dominated by Therophytes (59.5%). Chorotype spectra analysis revealed that Mediterranean, Saharo-Arabian, and Irano-Turanian were the most represented elements. The species richness and evenness were higher outside the canopy, which indicates a negative effect of the invasive shrub N. glauca on the plant biodiversity in the study area, particularly in Ar Ruddaf location. This could be attributed to the competition or allelopathic effect of N. glauca. In contrast, the density of N. glauca seeds was higher under the canopy compared to outside. The soil nutrients and moisture under the canopy were higher than outside canopy. The present study provides a deeper understanding of the most susceptible habitats or communities to the invasion by N. glauca and thereby open the challenge toward control of this noxious plant and vegetation restoration.

Storm runoff generation in headwater catchments on the Chinese Loess Plateau after long-term vegetation rehabilitation

Storm runoff is important for maintaining surface water resources, while this function is significantly affected by land use and land cover changes, e.g., afforestation and reforestation. The Chinese Loess Plateau (CLP) has undergone large-scale vegetation rehabilitation, especially afforestation over the past 20 years. We hypothesize that afforestation has profoundly changed the amounts and mechanisms of storm runoff generation in headwater catchments on the CLP. To test this hypothesis, rainfall, soil moisture, and streamflow were monitored in a grass catchment and an adjacent forest catchment for two consecutive years. The objective of this study was to elucidate the varied mechanisms of storm runoff generation in these two contrasting revegetated catchments. Results showed that (1) average runoff coefficient in the grassland catchment (0.042) was approximately ten times higher than that in the forestland catchment (0.004), confirming the impact of catchment afforestation on the suppression of storm runoff generation. (2) Peak rainfall intensity was the first-order control of the runoff coefficient in the grassland catchment, but not in the forestland catchment. (3) Threshold values for antecedent soil moisture (~18%) and the sum of antecedent soil moisture index and event precipitation (~210 mm) were identified in the grassland catchment, above which storm runoff significantly increased. (4) Two extraordinary high runoff coefficient events were observed in the grassland catchment, one due to high peak rainfall intensity and strong surface runoff and the other due to high rainfall amount and high antecedent soil moisture. We conclude that long-term afforestation has changed the mechanisms and patterns of storm runoff generation, and different conditions of rainfall intensity, rainfall amount and antecedent soil moisture determined the hydrological connectivity between the upper hillslope and downhill gully in the catchment. This study deepens our understanding of the mechanisms and thresholds of storm runoff generation in headwater catchments on the CLP.

Effects of revegetation on climate in the Mu Us Sandy Land of China

The ecological environment in China's arid and semi-arid regions has been improving over the past few decades. Using the Mu Us Sandy Land (MUSL) as a case study, we examine the consequent climate feedbacks and the impacts of revegetation on regional climate by incorporating high-resolution remote-sensing vegetation data into the WRF-Noah model. From 2001 to 2010, although a small portion of the grassland was degraded in MUSL, vegetation overall improved, with green fraction and leaf area index increased and surface albedo decreased. The model simulation suggests a cooling of the near-surface temperature by 0.12-0.32 °C on average and up to >0.5 °C in summer, with a reduction in nighttime minimum of 0.15-0.46 °C and in daytime maximum of <0.13 °C. The cooling is accompanied by a slight increase in 2-m air humidity. The near-surface cooling and wetting are induced by revegetation-enhanced evapotranspiration, but they have insignificant effect on the local precipitation. The results of this study imply that while revegetation has positive effects on the ecological systems in MUSL, it bears the cost of an increase in evapotranspiration of 51 mm per summer, which may exacerbate the water shortages in the region.

Loess Plateau: from degradation to restoration

United Nations established 2021-2030 as the decade for ecosystem restoration and "prevent, halt and reverse the degradation of ecosystems worldwide". Ecosystem and land degradation are a global phenomenon. As a consequence of land degradation, in the late 1990s, the "Grain for Green Program" (GFGP) was established in Loess Plateau (China). It converted slope farmlands to forest or grassland over the, resulting in a visible "greening" trend. Other effects of GFGP on soil properties, land production, hydrological conditions, ecosystem services, and policy implications are the topics of this Special Issue. This Special Issue includes 17 contributions that cover recent research carried out in Loess Plateau in the mentioned topics at different spatial and temporal scales. The collection of papers presented in this Special Issue discusses critical issues in vegetation restoration and sustainable land management in the region. This Special Issue will contribute to United Nations strategy for ecosystems restoration.

Effects of vegetation restoration on soil quality in fragile karst ecosystems of southwest China

Soil quality assessment is important for karst ecosystems where soil erosion is significant. A large amount of vegetation restoration has been implemented since the early 21st century in degraded karst areas across southwestern China. However, the impacts on soil quality of different restoration types rarely have been compared systematically. In the current study, we investigated the soil quality after a number of vegetation restoration projects as well as their adjacent cropland by analyzing soil samples. Six vegetation restoration types were evaluated, including one natural restoration (natural shrubland, protected for 13 years), three economic forests (4 years Eucalyptus robusta, 4 years Prunus salicina and 6 years Zenia insignis) and two mixed forests (1 year Juglans regia-crop and 13 years Toona sinensis-Pennisetum purpureum ). We evaluated the benefits of different restoration types more accurately by setting each adjacent cropland as the control and setting the variation between the corresponding restored and control site as the evaluation object so that the background differences of six sites could be eliminated. The results indicated that natural shrubland, Toona sinensis-Pennisetum purpureum and Zenia insignis were effective in improving soil quality index (SQI) in degraded karst cropland largely due to their higher SOC and TN content. The variation of SQI (VSQI) of natural shrubland was significantly higher than that in Eucalyptus robusta, Prunus salicina and Juglans regia-crop in total soil layer (0-30 cm) (P < 0.05), indicating natural shrubland had better capacity to improve soil quality. The boosting regression tree model revealed that vegetation restoration type explained 73.49% and restoration time explained 10.30% of the variation in VSQI, which confirmed that vegetation restoration type and restoration time are critical for achieving soil reserves. Therefore, it is vital to select appropriate vegetation type in restoration projects and recovery for a long time in order to achieve better soil quality. The current study provides a theoretical basis on which to assess the effects of different vegetation restoration types on the heterogeneous degraded karst areas.

Desertification reversion alters soil greenhouse gas emissions in the eastern Hobq Desert, China

Deserts cover more than 41% of the world's total land area and are significant in the terrestrial carbon cycle. The impact of desertification reversion and revegetation on the physical and chemical properties of soil is well studied; however, this study seeks to further the understanding of how they impact the flux of greenhouse gases (GHGs). Three sandy sites of different desertification reversal stages in the Hobq Desert were selected. Variations in the characteristics of GHG flux and its response mechanism to environmental hydrothermal conditions and soil properties were analyzed. Higher soil carbon dioxide (CO₂) emissions were observed in the growing season, whereas nitrous oxide (N₂O) emissions were mainly observed in the non-growing season. Methane (CH₄) absorption showed no obvious seasonal change. Linear regression analysis revealed that GHGs in the study area were positively correlated with total nitrogen and organic carbon content, and the number of microorganisms present in the soil. Hydrothermal factors were critical controllers of soil CO₂ emissions, but they did not majorly influence CH₄ and N₂O fluxes. The results illustrate the importance of desertification reversal and revegetation in mitigating climate change, and that deserts have a significant role in the global carbon cycle.

A framework to assess the impact of ecological water conveyance on groundwater-dependent terrestrial ecosystems in arid inland river basins

Overexploitation of water resources at middle reaches has threatened downstream oasis in arid inland river basins. To achieve sustainable development, ecological water conveyance is one effective measure to reallocate water resources between socio-economic and natural systems. A comprehensive impact assessment of ecological water conveyance on groundwater-dependent ecosystems that are common in downstream inland river basins is needed. The present study integrated the technologies of remote sensing analysis, trend detection, and numerical simulation into a technical framework that identifies the spatial response and temporal dynamics of vegetation to groundwater changes induced by ecological water conveyance. The Normalized Difference Vegetation Index (NDVI) was used as a proxy to estimate vegetation. The structure of the framework we used is clear and reasonable. We used remote-sensing data and ground truth information, and a decision tree that incorporates an iterative self-organizing data analysis technique. The decision tree classifies the land cover into affected and unaffected areas, and the results indicate the spatial range of impact. The Mann-Kendall algorithm and Sen's slope detect the tendency in NDVI series that indicates the temporal response of vegetation. The Verhulst logistic function, combined with environment carrying capacity function, constitutes a simplified vegetation dynamic model that can be used to predict potential impact through scenario analysis. An application in the Shiyang River basin in Northwest China evaluated the performance and usefulness of the framework; the accuracy of the results suggested that the framework is effective and practical. Additional case studies are required to assess the reliability and applicability of the framework and identify the factors that affect assessment results beyond our case study in the Shiyang River basin.