Loess Plateau: from degradation to restoration

Differential responses of vegetation phenology to climatic elements during extreme events on the Chinese loess plateau

Extreme, dry events have major impacts on vegetation phenology worldwide. However, the differential responses of vegetation phenology to climatic elements during these extreme events remain unclear. We investigated the response of vegetation phenology to climatic factors during extreme events in arid and semi-arid regions of the Chinese Loess Plateau, using the climate water deficit method, to identify extremely dry and wet events. The results revealed that extremely wet events extended the vegetation growth periods in addition to global warming, whereas extremely dry events did not completely counteract this effect. During different extreme events, phenological changes in vegetation on the Loess Plateau were primarily influenced by the interactive effects of climatic factors. During extremely dry events, a 100 mm increase in precipitation advanced the start of the season by 3.0, 9.2, and 16.7 days in forest, shrubland, and grassland, respectively. During extremely wet events, a 1 °C rise in temperature delayed the end of the season by 1.6, 0.6, and 3.8 days in forest, shrubland, and grassland, respectively. These findings provide crucial guidance for improving predictions of plant phenology changes under extreme climatic events and unraveling biosphere-atmosphere feedback cycles.

Quantification of the provenance contribution and sedimentary mixing effect of sediments in the Yellow River Basin, China

Quantifying the source contributions of sediments in large fluvial systems with active wind erosion problems has crucial implications for understanding morphological evolution and ecological progression in the Earth system. Much effort have been focused on characterizing sediments of the Yellow River, but quantitation of the sediment source proportions at the basin-wide scale is lacking. To this end, the research aims to quantitatively elucidate the potential source contributions of sediments in the Yellow River based on geochemical characteristics and sediment fingerprinting technique, in order to identify sedimentary mixing effect and propose sustainable development strategies. In total, samples of four source groups (n = 107) and target floodplain sediments (n = 61) were collected and tested for elemental composition, grain size, magnetic susceptibility, and quartz grain microtextures. The results indicated that the optimal tracer combination was determined as P, Zn, and Ca. The average contributions of the "Tibetan Plateau", "Sandy deserts-Loess Plateau", "Loess Plateau", and "Loess Plateau-Qinling Mountains" source groups to the target sediments were 23.0 %, 21.5 %, 31.6 %, and 23.9 %, respectively. The accuracy of source apportionments was supported by the goodness of fit (GOF) and virtual mixtures tests. Meanwhile, large amounts of debris from surrounding mountains was transported to the Loess Plateau through fluvial processes and ultimately mixed with aeolian deposits, leading to sedimentary mixing effect. To maintain water balance and minimize erosion risk, the drought-resistant perennial planting and moderate grazing were recommended. The findings are instrumental in promoting soil and water conservation and disclosing fluvial and aeolian interaction on a global scale.

Interguild fungal competition in litter and soil inversely modulate microbial necromass accumulation during Loess Plateau forest succession

Microbial interactions determine ecosystem carbon (C) and nutrient cycling, yet it remains unclear how interguild fungal interactions modulate microbial residue contribution to soil C pools (SOC) during forest succession. Here, we present a region-wide investigation of the relative dominance of saprophytic versus symbiotic fungi in litter and soil compartments, exploring their linkages to soil microbial residue pools and potential drivers along a chronosequence of secondary Chinese pine (Pinus tabulaeformis) forests on the Loess Plateau. Despite minor changes in C and nitrogen (N) stocks in the litter or soil layers across successional stages, we found significantly lower soil phosphorus (P) stocks, higher ratios of soil C: N, soil N: P and soil C: P but lower ratios of litter C: N and litter C: P in old (>75 years) than young stands (<30 years). Pine stand development altered the saprotroph: symbiotroph ratios of fungal communities to favor the soil symbiotrophs versus the litter saprotrophs. The dominance of saprotrophs in litter is positively related to microbial necromass contribution to SOC, which is negatively related to the dominance of symbiotrophs in soils. Antagonistic interguild fungal competition in litter and soil layers, in conjunction with increased fungal but decreased bacterial necromass contribution to SOC, jointly contribute to unchanged total necromass contribution to SOC with stand development. The saprotroph: symbiotroph ratios in litter and soil layers are mainly driven by soil P stocks and stand parameters (e.g., stand age and slope), respectively, while substrate stoichiometries primarily regulate microbial necromass accumulation and fungal: bacterial necromass ratios. These results provide novel insights into how microbial interactions at local spatial scales modulate temporal changes in SOC pools, with management implications for mitigating regional land degradation.

Simulating land use change for sustainable land management in China's coal resource-based cities under different scenarios

Land use competition among economic development, food security and ecological protection posed challenges for the sustainable development in resource-based cities, especially those represented by coal resource-based cities in China. Predicting future land use change under the coupled framework of shared socioeconomic pathways and representative concentration pathways (SSP-RCPs) was a crucial step in devising sustainable development strategies. In this study, the patch-generated land use simulation (PLUS) model coupled with SSP-RCP scenarios (SSP126, SSP245, SSP585) was used to predict land use changes from year 2020 to 2060, identify key management regions for balancing the goals of ecological protection and food security, and propose corresponding measures. The results showed that, (1) the selected driving factors and model parameters effectively simulated land use changes with an Overall accuracy of 0.95, a Kappa coefficient of 0.92, a Figure of Merit of 0.16, an Exchange error ≤5.69 %, a Shift error ≤1.04 %, and a Quantity error ≤0.67 %. (2) All the scenarios, it was observed that the grassland continued to decrease by 0.86 % to 7.34 %, and the forest and built-up land continued to increase, of which forest increased by 2.34 % to 4.03 %, and built-up land increased by 21.02 % to 61.08 %. Cropland only increased in SSP585 scenario, by 4.76 %, but declining by 2.93 % in SSP126 and SSP245 scenario. (3) In future scenarios, the expansion of built-up land has escalated the risk of cropland and grassland loss. Based on the distribution of key land use conversions, four categories of prioritized land management regions and corresponding measures have been proposed. This provided a potential pathway to mitigate risks associated with the protection of cropland and ecological land. Therefore, this study was instrumental in understanding the mechanisms of land use changes in coal resource-based cities, and provided a reference for land use planning.

Ecosystem degradation or restoration? The evolving role of land use in China, 2000-2020

Dramatic land use change in China affects ecosystem degradation and restoration. Identifying the evolving role of land use in ecosystem degradation and restoration in China is essential for sustainable land policy making. However, it is not clear how land use affects ecosystem degradation and restoration over time. Here, we used the revised benefit transfer approach and spatial statistics based on land use data to determine the evolving role that land use plays in ecosystem degradation and restoration in China during 2000-2020. The study results pointed out that the deterioration of the forestland ecosystem during the study period was the main reason for ecosystem degradation, while the conversion of arable land to forestland was the main cause for ecosystem restoration. Every 1% increase of land use intensity in the periods 2000-2005, 2005-2010, 2010-2015, and 2015-2020 resulted in -1.754%, 0.697%, 1.098%, and -0.058% of the changes in ecosystem services, respectively. This study provided important policy implications for future sustainable land use management in China.

Mapping ecosystem services in protected areas. A systematic review

Protected areas (PAs) supply ecosystem services (ES) essential for human wellbeing. Mapping is a critical exercise that allows an understanding of the spatial distribution of the different ES in PAs. This work aims to conduct a systematic literature review on mapping ES in PAs. In order to carry out this systematic review, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses method was applied. The results showed an increase in the number of works between 2012 and 2023, and they were especially conducted in Europe and Asia and less in North America, South America, and Oceania. Most studies were developed in terrestrial areas, and the International Union for Conservation of Nature classified them into types II and IV. Most of the works followed the Millennium Ecosystem Assessment classification and were mainly focused on the supply dimension. Regulating and maintenance and cultural ES were the most mapped dimensions in PAs. The most frequent provisioning ES mapped in PAs were Animals reared for nutritional purposes and Cultivated terrestrial plants grown for nutritional purposes. In regulating and maintenance, Maintaining nursery populations and habitats and Regulation of the chemical composition of the atmosphere and oceans were the most analysed. For cultural ES, Characteristics of living systems that enable activities promoting health, recuperation, or enjoyment through active or immersive interactions and Characteristics of living systems that enable aesthetic experiences were the most mapped ES in PAs. Most works followed a quantitative approach, although the number of qualitative studies is high. Finally, most of the works needed to be validated, which may hamper the credibility of mapping ES in PAs. Overall, this systematic review contributed to a global picture of studies distribution, the areas where they are needed, and the most popular dimensions and sections as the methodologies were applied.

Mapping and assessment of ecosystem health in the Vilnius functional zone (Lithuania)

Urban expansion is a global phenomenon that impacts biodiversity loss and climate change. Soil sealing increases land degradation and the ecosystem services supply. This degradation also negatively affects ecosystem health, essential to make cities more sustainable and liveable. This work aims to study the ecosystem health spatiotemporal evolution (1990, 2000, 2006, 2012 and 2018) in the Vilnius (Lithuania) functional zone, using the vigour, organisation and resilience (VOR) method. The results showed that ecosystem health model validation was acceptable (r = -0.761; p < 0.01). Between 1990 and 2018, an increase (18.37 %) in ecosystem vigour was observed. The values were significantly higher in 2006, 2012 and 2018 than in 1990 and 2000. We identified a decrease between 1990 and 2018 regarding ecosystem organisation (7.15 %) and resilience (9.92 %). However, no significant differences between the years were identified. Ecosystem health decreased (11.49 %) between 1990 and 2018, mainly between 2012 and 2018. Ecosystem health values in 2018 were significantly lower than those identified in the previous years. The lowest values of ecosystem vigour, organisation and resilience were identified in the Vilnius city centre, while the highest was observed in the Vilnius functional zone. From 1990 to 2018, ecosystem vigour increased in some elderships located on the fringe of the studied area due to land abandonment and forest plantations. Simultaneously, a decrease in ecosystem organisation and resilience in the elderships located in Vilnius city centre was observed due to urban sprawl and the consequent landscape fragmentation. This negatively impacted ecosystem health, overshadowing the positive trend observed in ecosystem vigour. Different processes (e.g., urban sprawl, land abandonment, forest plantations) occurred in the Vilnius functional zone. It is essential to halt urban expansion and its adverse impacts on ecosystem health, city sustainability and liveability.

Influence of organic fertilization on growth and yield of strawberry (Fragaria × ananassa) in Kabete and Mbooni areas, Kenya

Strawberries are a valuable crop in Kenya with the potential for significant economic contributions. However, strawberry production in the country has been facing considerable challenges, impacting its economic potential. This study examined the influence of organic manure on strawberry growth and characteristics in Kabete and Mbooni areas in Kenya. The study used a randomized complete block design (RCBD) with three replications. Treatments included livestock manure (well composted mixture of chicken, goat, and cow manure), bokashi manure, and a control, coded as LivManure, BokManure and Control, respectively. Growth parameters including leaf area, number of white flowers and number of runners, as well as yield parameters such as the number and weight of strawberries were assessed from the 3rd to 10th week after transplanting, during the short rain season of 2021. Using R statistical software, linear models were fitted to datasets from both study sites and analyzed using one-way ANOVA, followed by post-hoc tests for multiple comparisons. The rigorous analysis of the Kabete and Mbooni datasets provided insightful revelations about the influence of different treatments on strawberry characteristics, and geographical disparities between the two regions. The analysis of variance (ANOVA) outcomes unveiled significant treatment effects in both sites, with F(2,69) = 62.57, p < 0.001 for Kabete and F(2,69) = 49.02, p < 0.001 for Mbooni, highlighting distinct influences of treatments on log values within each group. Post hoc analyses, including Tukey tests and bootstrap comparisons robustly validated the significant differences among the three treatments in each site, supported by p-values <0.001. Effect sizes were also employed to reinforce the findings, and planned contrasts were set to gain more power in the analysis of variance. Comparison between Kabete and Mbooni indicated a significant difference of 9.78 units, with Mbooni area exhibiting significantly higher strawberry characteristics compared to Kabete. The results showed that LivManure treatment had the highest mean in both sites, followed by BokManure and Control treatments, respectively. These findings have important implications for agriculture, and highlight the potential benefits of using LivManure treatment to improve strawberry characteristics in similar agroclimatic settings. These observations can be attributed to the beneficial effects of livestock manure on soil health, which include buffering of the soil reaction, provision of essential plant nutrients and enhancement of soil faunal activities. Balanced use of livestock manure is recommended to enhance soil macro and micronutrients, and soil reaction for improved growth and yield of strawberry.

Modeling soil loss under rainfall events using machine learning algorithms

Soil loss is an environmental concern of global importance. Accurate simulation of soil loss in small watersheds is crucial for protecting the environment and implementing soil and water conservation measures. However, predicting soil loss while meeting the criteria of high precision, efficiency, and generalizability remains a challenge. Therefore, this study first used three machine learning (ML) algorithms, namely, random forest (RF), support vector machine (SVM), and artificial neural network (ANN) to develop soil loss models and predict soil loss rates (SLRs). These soil loss models were constructed using field observation data with an average SLR of 1756.48 t/km2 from rainfall events and small watersheds in the hilly-gully region of the Loess Plateau, China. During training, testing and generalizability stages, the average coefficients of determination from the RF, SVM, and ANN models were 0.903, 0.860, and 0.836, respectively. Similarly, the average Nash-Sutcliffe coefficients of efficiency from the RF, SVM and ANN models were 0.893, 0.791 and 0.814, respectively. These results indicated that MLs have superior predictive performance and generalizability, and broad prospects for predicting SLRs. This study also demonstrated that the RF model outperformed better than the SVM and ANN models. Therefore, the RF model was used to simulate the SLR of each small watershed in the Chabagou watershed. Our results showed the four-year (2017-2020) average annual SLR of the small watersheds ranged from 0.73 to 1.63 × 104 t/(km2∙a) in the Chabagou watershed. Additionally, the results also indicated the SLR of small watersheds under the rainstorm event with a 100-year recurrence interval was 4.4-51.3 times that of other rainfall events.Furthermore, this study confirmed that bare land was the predominant source of soil loss in the Chabagou watershed, followed by cropland land and grassland. This study helps to provide the theoretical basis for deploying soil and water conservation measures to realize the sustainable utilization of soil resources in the future.

Plant functional traits explain long-term differences in ecosystem services between artificial forests and natural grasslands

Declining ecosystem services have prompted numerous studies aiming at developing more sustainable management practices for vegetation restoration. Advances in functional ecology indicate that the sustainable management of afforestation ecosystems should be performed based on plant functional traits, which provides pivotal knowledge for long-term sustainable vegetation restoration. Currently, the mechanism of how plant functional traits affect long term ecosystem services in restored areas is still unclear. This study investigates plant functional traits and the associated ecosystem services from artificial forestlands (Robinia pseudoacacia, Caragana korshinskii) and natural grasslands following different durations of vegetation restoration (10, 20, 30 and 40 years) in the Danangou watershed, a loess hilly-gully region in the Loess Plateau, China. The results showed that 1) the water conservation services of artificial forestlands first decreased and then increased over time, whereas the soil conservation service had an opposite trend; in turn, natural grassland led to a consistent increase in soil conservation and carbon sequestration services over time. 2) Artificial forestlands had greater soil conservation and carbon sequestration services than natural grassland but had lower water conservation services. 3) Leaves had a greater impact on carbon sequestration and water conservation services than did root length and root biomass density. 4) Root biomass density had a greater effect on soil conservation services than did leaf carbon content and soil organic matter. 5) Leaf carbon content, specific root length, and root biomass density had significant effects on the trade-off value between any two ecosystem services with increasing time after restoration of artificial forestland. 6) Specific leaf area had a greater effect on the trade-off values among the three services than did the other functional traits in the natural grassland. In arid ecosystems, natural grasslands are the best restoration strategy given their higher water conservation services. However, in soil erosion-affected areas, restoration through artificial forestlands is more appropriate. To mitigate the trade-offs between ecosystem services, it is recommended that artificial forestlands be thinned before the leaf carbon content, specific root length, and root biomass density reach a maximum (i.e., mature forestland).

Coupling strength of human-natural systems mediates the response of ecosystem services to land use change

Addressing the dynamics of human-natural systems (HNS) driven by land use change (LC) is a key challenge for the sustainable development of ecosystem services (ES). However, how changes to the HNS coupling relationships affect ES is rarely reported. We used network analysis methods to construct an HNS correlation network in the Loess Plateau based on the correlation between the main components of HNS, such as ES, human factors, landscape pattern, vegetation cover, climate change and geomorphic characteristics, and quantitatively described the HNS coupling relationships through key network attributes. We analyzed the variation in HNS network attributes and their relationships with ES along an LC intensity gradient. The results show that carbon storage and soil conservation in the Loess Plateau increased by 0.56% and 0.26%, respectively, during the study period, while the habitat quality and water yield decreased by 0.11% and 0.18%, respectively. An increase in LC intensity reduces connectivity and density in the HNS network, which results in looser connections among HNS components. Importantly, we found that HNS network attributes explained 85% of ES variation across different LC intensity gradients and that connectivity and density had the strongest explanatory power. This means that LC mainly affects ES dynamics by changing the coupling strength of HNS. Our research offers a new perspective for linking LC-HNS-ES, which will help guide practitioners toward establishing and maintaining the sustainability of human well-being amidst changing HNS.

Climatic Warming-Induced Drought Stress Has Resulted in the Transition of Tree Growth Sensitivity from Temperature to Precipitation in the Loess Plateau of China

Ongoing climate warming poses significant threats to forest ecosystems, particularly in drylands. Here, we assess the intricate responses of tree growth to climate change across two warming phases (1910-1940 and 1970-2000) of the 20th century in the Loess Plateau of China. To achieve this, we analyzed a dataset encompassing 53 ring-width chronologies extracted from 13 diverse tree species, enabling us to discern and characterize the prevailing trends in tree growth over these warming phases. The difference in the primary contributors over two warming phases was compared to investigate the association of tree growth with climatic drivers. We found that the first warming phase exerted a stimulating effect on tree growth, with climate warming correlating to heightened growth rates. However, a contrasting pattern emerged in the second phase as accelerated drought conditions emerged as a predominant limiting factor, dampening tree growth rates. The response of tree growth to climate changed markedly during the two warming phases. Initially, temperature assumed a dominant role in driving the tree growth of growth season during the first warming phase. Instead, precipitation and drought stress became the main factors affecting tree growth in the second phase. This drought stress manifested predominantly during the early and late growing seasons. Our findings confirm the discernible transition of warming-induced tree growth in water-limited regions and highlight the vulnerability of dryland forests to the escalating dual challenges of heightened warming and drying. If the warming trend continues unabated in the Loess Plateau, further deterioration in tree growth and heightened mortality rates are foreseeable outcomes. Some adaptive forest managements should be encouraged to sustain the integrity and resilience of these vital ecosystems in the Loess Plateau and similar regions.

Differences in soil water storage, consumption, and use efficiency of typical vegetation types and their responses to precipitation in the Loess Plateau, China

After massive afforestation, the Loess Plateau is facing the severe challenge of water shortages. Water use efficiency (WUE) is an important indicator of plant drought resistance, and high WUE is an important way to reconcile the contradiction between vegetation growth and soil water consumption (SWC). Different vegetation types significantly influence hydrological cycle process and WUE. In this study, the Biome-BGC model was used to simulate and analyze the soil water storage (SWS), SWC, and WUE of 3 typical vegetation types in the Loess Plateau from 2005 to 2020. The results showed that the order of SWS of different vegetation types from largest to smallest was grassland (GL, 81.82 mm/day), abandoned farmland (AF, 66.92 mm/day), and Robinia pseudoacacia forest (RP, 55.64 mm/day); SWC was RP (480.09 mm/year), GL (464.68 mm/year), and AF (421.79 mm/year); WUE was RP (2.37 gC/kgH₂O), GL (1.10 gC/kgH₂O), and AF (0.60 gC/kgH₂O). GL showed a better water retention capacity. Precipitation recharge did not meet the full SWC of vegetation. In years of high vegetation growth, as well as in the dry season when water was scarce, both RP and GL showed varying degrees of water deficit. Correlation analysis revealed that a positive effect of precipitation on WUE has a threshold effect, and the thresholds range from approximately 15-50 mm/day for RP, 15-25 mm/day for GL, and no clear pattern for AF. Overall, in water-stressed areas, a large expansion of forest land should be reduced and GL should be increased. In seasons and areas where vegetation is growing vigorously or extremely arid, irrigation regarding precipitation thresholds should be carried out to improve the WUE of vegetation and promote the sustainable development of regional ecology.

Ecosystem carbon sequestration service supports the Sustainable Development Goals progress

Ecosystem carbon sequestration service (ECSS) is the benefits humans derive from the ecosystem carbon sequestration process, which is key to regulating climate, stabilising the natural foundation for development, and supporting the Sustainable Development Goals (SDGs) achievement. However, how ECSS contributes to the SDGs still needs to be discovered. Here, based on downscaling localisation SDG indicators, regression methods, and mechanism analysis, we identified the contribution of ECSS to the SDGs, taking China's Loess Plateau (LP) region as an example. The results showed that the LP made higher progress on resource and environmental SDGs, such as SDGs 13, 12, 6, and 7 (climate, consumption and production, water, and energy) in the last two decades. As for the relationships between ECSS and SDGs, the progress of SDGs 6, 7, 13 and 15 (water, energy, climate, and ecosystems) showed positive linear responses to ECSS. The response of SDGs 1, 4, 8, and 12 (poverty reduction, education, economic growth, and consumption and production) to ECSS showed a threshold when the standardised ECSS value was 0.11. To improve ECSS for a more sustainable ecological foundation underpinning the SDGs, ECSS management should be improved to protect the ecosystem carbon pool and improve carbon sequestration function, as well as to promote the social-ecological co-benefits. This work links carbon sequestration service to sustainable development and can help in leveraging nature's contributions towards carbon neutrality and the 2030 Agenda.

Effect of Shrub Components on Soil Water and Its Response to Precipitation at Different Time Scales in the Loess Plateau

Water shortages have become the major limiting factor for ecological protection and sustainable development in the Loess Plateau. Few studies have focused on the effects of different plant components on soil water and its response to precipitation at different time scales. This study conducted an observation of shrub plants with three treatments (natural condition (NC), canopy + roots after removing the litter (CR), and only roots (OR)) to monitor the dynamics of soil water during the rainy season of an extreme drought year in 2015. The results showed that the soil moisture content (SMC) and soil water storage (W) had a trend of OR > CR > NC. The response of the SMC to precipitation was gradually decreased and delayed for longer with increasing soil depth. Daily precipitation >10 mm was the threshold to trigger an SMC response below 20 cm of depth. The thresholds of precipitation to increase W were 2.09-2.54 mm at the daily scale and 29.40-32.56 mm at the monthly scale. The effect of precipitation on W and its change (∆W) also depended on the time scales. At the daily scale, precipitation only explained 1.6%, 0.9%, and 2.4% of the W variation in NC, CR, and OR, respectively. However, precipitation was more important for ∆W, making a contribution of 57.6%, 46.2%, and 56.6%, respectively, and the positive ∆W induced by precipitation happened more easily and frequently at deeper depths in OR. At the monthly scale, the contribution of precipitation to ∆W increased to 75.0%, 85.0%, and 86%, respectively. The ∆W of the whole rainy season was OR > NC > CR. Precipitation of the monthly scale displayed higher contributions to soil water than that of the daily scale. Plant components had different influences on soil water and its response to precipitation, which was strengthened by the roots, weakened by the canopy, and neutralized by the litter. Regular cutting of the canopy at the single-shrub scale may help increase water storage, which is useful for vegetation management and hydrologic regulation.

Dramatic shift in the drivers of ecosystem service trade-offs across an aridity gradient: Evidence from China's Loess Plateau

Increased aridity creates challenges for sustainable ecosystem management due to the potential for trade-offs among ecosystem services. However, our understanding of how ecosystem service trade-offs (EST) respond to aridification remains limited. Here, generalized additive models and structural equation modeling were used to explore EST dynamics within an aridity gradient on the Loess Plateau, China. Trade-offs between water yield and both carbon storage and habitat quality showed nonlinear relationships with aridity, first increasing and then decreasing. Interestingly, climatic and human factors mostly indirectly influenced EST via effects on landscape characteristics. In regions with an Aridity Index (AI) value of <0.5, climatic and human factors strongly drove EST; in regions with AI > 0.5, landscape characteristics were most important. Therefore, landscape characteristics acted as the key regulators of EST. Importantly, AI values of ∼0.5 represented a transition point, after which dramatic shifts in EST-driver relationships were observed. As >22 % of the Earth's terrestrial surface is projected to reach this level of aridity by 2100, further research on this boundary (between sub-humid and semi-arid areas) is urgently needed to protect ecosystems from the effects of increasing aridity. This study may serve as a valuable reference for mitigating the potential negative effects of increased aridity on human well-being.

Soil temperature, microbial biomass and enzyme activity are the critical factors affecting soil respiration in different soil layers in Ziwuling Mountains, China

Soil microorganisms are critical biological indicators for evaluating soil health and play a vital role in carbon (C)-climate feedback. In recent years, the accuracy of models in terms of predicting soil C pools has been improved by considering the involvement of microbes in the decomposition process in ecosystem models, but the parameter values of these models have been assumed by researchers without combining observed data with the models and without calibrating the microbial decomposition models. Here, we conducted an observational experiment from April 2021 to July 2022 in the Ziwuling Mountains, Loess Plateau, China, to explore the main influencing factors of soil respiration (R_S) and determine which parameters can be incorporated into microbial decomposition models. The results showed that the R_S rate is significantly correlated with soil temperature (T_S) and moisture (M_S), indicating that T_S increases soil C loss. We attributed the non-significant correlation between R_S and soil microbial biomass carbon (MBC) to variations in microbial use efficiency, which mitigated ecosystem C loss by reducing the ability of microorganisms to decompose organic resources at high temperatures. The structural equation modeling (SEM) results demonstrated that T_S, microbial biomass, and enzyme activity are crucial factors affecting soil microbial activity. Our study revealed the relations between T_S, microbial biomass, enzyme activity, and R_S, which had important scientific implications for constructing microbial decomposition models that predict soil microbial activity under climate change in the future. To better understand the relationship between soil dynamics and C emissions, it will be necessary to incorporate climate data as well as R_S and microbial parameters into microbial decomposition models, which will be important for soil conservation and reducing soil C loss in the Loess Plateau.

Spatiotemporal variations and relationships of absorbing aerosol-radiation-gross primary productivity over China

High-load carbonaceous and dust aerosols can significantly reduce direct radiation (DIRR), which would affect photosynthesis in terrestrial ecosystems, thereby further affecting the productivity of vegetation. Based on this, a variety of remote sensing data were used to study the spatiotemporal distributions and changing tendencies of the absorbing aerosols, CO, DIRR, and gross primary productivity (GPP) in China during 2005-2019; then, the relationships were analyzed between different types of absorbing aerosols and DIRR as well as GPP. The results showed that the annual mean absorbing aerosols index (AAI) in China during 2005-2019 was 0.39, with a slow growth rate of 0.02 year^-1, and the emission of CO showed a decreasing trend with each passing year, especially in North China Plain and Sichuan Basin. Carbonaceous and dust aerosols were predominantly bounded by Hu line. The east of Hu line was the dominant area of carbonaceous aerosols, and the west of Hu line was the topographical region of dust aerosols. Near the Hu line was the dominant area of carbonaceous-dust aerosols. However, the Karamay-Urumqi-Hami area and Northeast China Plain were exceptional. During the vegetation growing season, different types of absorbing aerosols significantly negatively affected GPP. From a perspective of regional scale variation pattern, the negative effect of absorbing aerosols on vegetation productivity was the most significant in Northeast China; from the perspective of the effects of different vegetation types, the negative effect of absorbing aerosols on grasslands was greater than that of woodlands; from the perspective of the composition characteristics of aerosols, the negative effect of dust aerosols on GPP was greater than that of carbonaceous aerosols.

Years of sand fixation with Caragana korshinskii drive the enrichment of its rhizosphere functional microbes by accumulating soil N

C. korshinskii is one of the most widely-planted sand-fixing legumes in northwest China and exploring its rhizosphere microbiome is of great ecological importance. However, the effect of long-term sand fixation on the composition, diversity, and underlying functions of microbes in the C. korshinskii rhizosphere in dryland ecosystems remain unclear. Here, we performed high-throughput sequencing using a 16S rRNA (absolute quantification) and bacterial functional annotation of prokaryotic taxa (FAPROTAX) analysis and an ITS (relative quantification) and fungal functional guild (FUNGuild) analysis to investigate the C. korshinskii rhizosphere microbiome and metabolic functional groups at different sand-fixing ages (six years, CK6; twelve years, CK12; and eighteen years, CK18) and determined the physicochemical properties of the rhizosphere soil. Results showed that the key bacterial taxa of the rhizosphere were significantly more abundant in CK18 than in CK12 and CK6 at the phylum-class-genus level, and that fungal Glomeromycota was also significantly more abundant in the CK18 rhizosphere compared to CK12 and CK6. Among these bacterial taxa, the enrichment effect of key, functional, genus-level species of bacteria was the most obvious, including Rhizobium, Ensifer, Neorhizobium, Mesorhizobium, Streptomyces, Sphingomonas, and Flavobacterium, which are N-fixing and/or phosphate-solubilizing groups. The significant improvement seen in the physicochemical properties of the CK18 rhizosphere soil, including the higher total nitrogen (TN), available nitrogen (AN), pH, electrical conductivity (EC), higher N:P ratio, and lower C:N ratio, all demonstrated the relationship between the rhizosphere microbes and soil carbon (C) and nitrogen (N) cycling. A redundancy analysis (RDA) of different taxonomic levels indicated a close positive relationship between rhizosphere microbes and AN. In addition, the functional groups of the C. korshinskii rhizosphere bacteria were closely related to soil AN and were mainly composed of chemoheterotrophy and aerobic chemoheterotrophy. A Spearman correlation analysis revealed that these functional groups were mainly identified from bacterial Actinobacteria, Proteobacteria, Verrucomicrobia, Bacteroidetes, and fungal Glomeromycota. Our study provides evidence that the rhizosphere microbes of C. korshinskii are closely related to the accumulation of N in the restoration of desert ecosystems, and that the ecological functional processes they are involved in mainly involve C and N cycles, which play an important role in desertification reversal.

Ecosystem restoration is integral to humanity's recovery from COVID-19

COVID-19 has devastated global communities and economies. The pandemic has exposed socioeconomic disparities and weaknesses in health systems worldwide. Long-term health effects and economic recovery are major concerns. Ecosystem restoration-ie, the repair of ecosystems that have been degraded-relates directly to tackling the health and socioeconomic burdens of COVID-19, because stable and resilient ecosystems are fundamental determinants of health and socioeconomic stability. Here, we use COVID-19 as a case study, showing how ecosystem restoration can reduce the risk of infection and adverse sequelae and have an integral role in humanity's recovery from COVID-19. The next decade will be crucial for humanity's recovery from COVID-19 and for ecosystem repair. Indeed, in the absence of effective, large-scale restoration, 95% of the Earth's land could be degraded by 2050. The UN Decade on Ecosystem Restoration (2021-30) declaration reflects the growing urgency and scale at which we should repair ecosystems. Importantly, ecosystem restoration could also help to combat the health and socioeconomic issues that are associated with COVID-19, yet it is poorly integrated into current responses to the disease. Ecosystem restoration can be a core public health intervention and assist in COVID-19 recovery if it is closely integrated with socioeconomic, health, and environmental policies.

Ecological restoration stimulates environmental outcomes but exacerbates water shortage in the Loess Plateau

Restoration is the natural and intervention-assisted set of processes designed to promote and facilitate the recovery of an ecosystem that has been degraded, damaged, or destroyed. However, it can also have an adverse effect on the environment. Thus, assessing an ecological restoration project's impact is crucial to determining its success and optimum management strategies. We performed a meta-analysis concerning the environmental outcomes during the years 2000-2015 resulting from the "Grain for Green" Project (GFGP) implementation in the Loess Plateau (LP). Data were gathered from 40 peer-reviewed English-language articles chosen from a pool of 332 articles. The results showed that, on average, GFGP increased forest coverage by 35.7% (95% CI [24.15-47.52%]), and grassland by 1.05% (95% CI [0.8-1.28%]). At the same time, GFGP has a positive impact on soil carbon (C) sequestration, net ecosystem production (NEP), and net primary production (NPP), from the years 2000 to 2015 by an average of 36% (95% CI [28.96-43.18%]), 22.7% (95% CI [9.10-36.79%]), and 13.5% (95% CI [9.44-17.354%]), respectively. Soil erosion, sediment load, runoff coefficient, and water yield were reduced by 13.3% (95% CI [0.27-25.76%]), 21.5% (95% CI [1.50-39.99%]), 22.4% (95% CI [5.28-40.45%]) and 43.3% (95% CI [27.03-82.86%]), respectively, from the years 2000 to 2015. Our results indicate that water supply decreased with the increase of vegetation coverage. Therefore, to balance the needs for green space, GFGP policies and strategies should recover, enhance, and sustain more resilient ecosystems.

Effects of Plastic Film Mulching on Soil Enzyme Activities and Stoichiometry in Dryland Agroecosystems

Soil extracellular enzymes are pivotal for microbial nutrient cycling in the ecosystem. In order to study the effects of different nitrogen application rates under plastic film mulching on soil extracellular enzyme activities and stoichiometry, five nitrogen application levels (i.e., 0, 90, 150, 225 and 300 kg·hm⁻²) were set based on two treatments: plastic film mulching (PM) and no film mulching (LD). We measured the soil extracellular enzyme activities (EEAs) and stoichiometry (EES) of four enzymes (i.e., β-1,4-glucosidase (βG), leucine aminopeptidase (LAP), β-1,4-N-acetylaminoglucosidase (NAG) and alkaline phosphatase (AP)) involved in the C, N and P cycles of soil microorganisms in surface soil at five maize growth stages (seedling stage, jointing stage, trumpet stage, grout stage and harvest stage). The results showed that there were significant differences in soil EEA at different maize growth stages. The soil nutrient content and soil EEA were significantly improved under PM, and the stoichiometric ratio of extracellular enzymes (E_C:N:P) was closer to 1:1:1, which indicated that PM was beneficial to the balance of soil nutrients and the activity of microorganisms. At each stage, with the increase in nitrogen application levels, the soil EEA showed a trend of increasing first and then decreasing (or remained unchanged), and both LD and PM treatments reached their highest activity at the 225 kg·hm⁻² nitrogen application rate. When the nitrogen application level was less than 225 kg·hm⁻², the soil enzyme activity was mainly limited by the N nutrient, and when the nitrogen application level reached 300 kg·hm⁻², it was mainly limited by the P nutrient. RDA and correlation analysis showed that the soil C:P, C:N, N:P and pH had significant effects on soil βG, NAG + LAP and AP activities as well as E_C:N, E_C:P and E_N:P.

Evaluation of the Ecological Effects of Ecological Restoration Programs: A Case Study of the Sloping Land Conversion Program on the Loess Plateau, China

The Sloping Land Conversion Program (SLCP) is the largest ecological restoration program in the world. Evaluating the ecological effects of the SLCP not only provides a scientific basis for China to improve the SLCP but also provides a reference for other countries in the world to evaluate the ecological effects of ecological restoration programs being implemented or to be implemented. To this end, we took the Loess Plateau, the core area for the implementation of the SLCP, as an example and, based on multi-source remote sensing data and GIS technology, we conducted a comprehensive evaluation of the ecological effects of the implementation of the SLCP on the Loess Plateau. The results showed that, first, from 2000 to 2018, a total of 12,372.05 km² of cultivated land was converted into forest land and grassland on the Loess Plateau, and this contributed to an increase in vegetation cover from 45.09% in 2000 to 64.15% in 2018, and a decrease in the soil erosion modulus from 26.41 t·hm⁻²·yr⁻¹ in 2000 to 17.92 t·hm⁻²·yr⁻¹ in 2018. Second, the 6–25° slope range is the core area of the Loess Plateau for implementation of the SLCP. In this range, the area of cultivated land converted into forest land and grassland accounts for 60.16% of the total area of transferred cultivated land. As a result, the 6–25° slope range has become the most significant area for improving vegetation cover and reducing the soil erosion intensity, and it is mainly concentrated in the southwestern, central and central-eastern hilly and gully areas of the Loess Plateau. Third, from 2000 to 2018, the climate of the Loess Plateau tended to be warm and humid and was conducive to the implementation of the SLCP. Among these factors, precipitation is the dominant factor in determining the spatial distribution of vegetation on the Loess Plateau, and the increase in precipitation is also the main reason for the promotion of vegetation growth. Fourthly, from 2000 to 2018, the ecological environment of the Loess Plateau was significantly improved as a result of the combined effects of the implementation of the SLCP and climate warming and humidification, but the primary reason is still the implementation of the SLCP.

Legume Integration Augments the Forage Productivity and Quality in Maize-Based System in the Loess Plateau Region

The changing climate, inadequate water supply, insufficient agricultural inputs, decreasing in agricultural arable land areas under forage crops of Northwestern Loess Plateau region, expanding livestock population, increasing demands for meat and milk production, and food and feed security concerns all insist on a necessary requirement in forage quality production. Cereal–legume mixed-cropping is a biological approach to enhancing herbage yield and quality of upgraded animal feed (forage and silage). However, little information exists about the appropriate mixing seeding ratios and its impacts on yield and quality. Therefore, this study was conducted to examine the forage yield and nutritional quality of maize (Zea mays L.) and common bean (Phaseolus vulgaris L.) in mono-and mixed-cropping approaches at the seeding proportions of 100:0, 75:25, 50:50, 45:55, 25:75, and 0:100 in 2019 and 2020 in Northwestern Loess Plateau region. A randomized complete block design with four replicates was used in this experiment. The results indicated that forage quality was significantly affected by the mixture ratios. The land equivalent ratio (LER) of all mixed-cropping treatments greater than 1.0, in which maize–common bean at the 50:50 seeding ratio achieved higher LER (1.46) than that of other treatments, showing that mixed-cropping combination systems are better users of land resources. Laboratory forage quality analysis and Pearson correlation analysis showed that the relative feed value had highly positive correlation with total digestible nutrients and relative forage quality in mixed-cropping treatments. Our results showed that fresh forage yield and dry matter yield were higher in monocropped maize forage than in other intercropped forages, whereas crude protein yield was lower compared with other mixed cropping forages. After 60 days of ensiling, the highest organic acid profile and ammonia-nitrogen were observed in M25:CB75 silage compared with other silages. The highest ensilability of fermentation coefficient was also found in M50:CB50 compared with other intercropped silages. Regarding forage preservation, silage showed higher contents of crude protein, relative feed value and lower crude fiber, water-soluble carbohydrate neutral detergent fiber, and acid detergent fiber contents than forage. This study determined that the ratios of maize–common bean 25:75 and 50:50 were the most desirable mixture ratios among mixed-cropped forage and silage based on chemical composition and quality analysis for livestock feeding.

Large-Scale Detection of the Tableland Areas and Erosion-Vulnerable Hotspots on the Chinese Loess Plateau

Tableland areas, featured by flat and broad landforms, provide precious land resources for agricultural production and human settlements over the Chinese Loess Plateau (CLP). However, severe gully erosion triggered by extreme rainfall and intense human activities makes tableland areas shrink continuously. Preventing the loss of tableland areas is of real urgency, in which generating its accurate distribution map is the critical prerequisite. However, a plateau-scale inventory of tableland areas is still lacking across the Loess Plateau. This study proposed a large-scale approach for tableland area mapping. The Sentinel-2 imagery was used for the initial delineation based on object-based image analysis and random forest model. Subsequently, the drainage networks extracted from AW3D30 DEM were applied for correcting commission and omission errors based on the law that rivers and streams rarely appear on the tableland areas. The automatic mapping approach performs well, with the overall accuracies over 90% in all four investigated subregions. After the strict quality control by manual inspection, a high-quality inventory of tableland areas at 10 m resolution was generated, demonstrating that the tableland areas occupied 9507.31 km2 across the CLP. Cultivated land is the dominant land-use type on the tableland areas, yet multi-temporal observations indicated that it has decreased by approximately 500 km2 during the year of 2000 to 2020. In contrast, forest and artificial surfaces increased by 57.53% and 73.10%, respectively. Additionally, we detected 455 vulnerable hotspots of the tableland with a width of less than 300 m. Particular attention should be paid to these areas to prevent the potential split of a large tableland, accompanied by damage on roads and buildings. This plateau-scale tableland inventory and erosion-vulnerable hotspots are expected to support the environmental protection policymaking for sustainable development in the CLP region severely threatened by soil erosion and land degradation.

Hydrogeochemistry Characteristics of Groundwater in the Nandong Karst Water System, China

The hydrogeochemical characteristics of groundwater are an important element in the study of the spatial and temporal variation of groundwater resources, which is crucial to water resources utilization, ecological environmental protection, and human development. Water samples were collected at eight observation of Nandong Karst Water System (NKWS) sites in each month of 2019, and the main ions and isotopes of the water samples were examined. The hydrogeochemistry characteristics of groundwater and its differences with surface water were explored by using the methods of multivariate statistics, Gibbs model. Results showed that the water chemistry types of groundwater were mainly HCO3 – Ca and HCO3 –Ca· Mg. The analysis of hydrogen and oxygen isotope showed that the initial recharge source of surface water and groundwater were atmospheric precipitation, and the measured hydrogen and oxygen isotopes of surface water were heavier due to the strong evaporation effect. The natural and anthropogenic processes contributed to the chemical composition of surface water and groundwater in the study area. However, the main factor affecting the quality of surface water and groundwater was the input of anthropogenic contaminants. In terms of natural factors, the main chemical ions of surface water and groundwater were mainly controlled by water–rock action originating from weathering and hydrolysis of rocks and soils. Ca2+, Mg2+, and HCO− 3 mainly originated from natural dissolution of carbonate rocks. K+, Na+, SO2− 4, and Cl− were partly from atmospheric precipitation. For human activities, Na+ and Cl− were partly from domestic water for local residents. SO2− 4 in surface water mainly came from mining. NO− 3 in groundwater mainly came from chemical fertilizers, and NO− 3 in surface water were mainly from human waste and domestic sewage.

The Characteristics of Radial Growth and Ecological Response of Caragana korshinskii Kom. Under Different Precipitation Gradient in the Western Loess Plateau, China

Understanding the temporal-spatial variability of tree radial growth and ecological response is the basis for assessing forest vulnerability in sight of climate change. We studied stands of the shrub Caragana korshinskii Kom. at four sampling sites (natural forest CL and plantation forests XZJ, CK and TPX) that spanned the different precipitation gradient (180-415 mm) across China's western Loess Plateau, and demonstrated its radial growth dynamics and ecological response. We found that the growth of natural C. korshinskii in arid regions have adapted and cope with regional environmental changes and radial growth was less affected by drought stress. However, the growth of planted C. korshinskii was significantly affected by drought stress in arid and semi-arid regions, especially during the growing season (from June to September). Variations in radial growth rates and growth indicators such as shrub height, canopy area are consistent with the climate-growth relationship. With increase of precipitation, the limiting of drought on the growth of planted C. korshinskii gradually decreased and the amount of radial growth variation explained by drought decreased from 53.8 to 34.2% and 22.3% from 270 to 399 and 415 mm of precipitation, respectively. The age-related radial growth trend shows that radial growth increased until 4 years of age, then decreased rapidly until 12-14 years of age, and then eventually tend to stabilized. In the context of climate warming and humidification, increased precipitation and regular branch coppicing management at around 12 years old will help to mitigate the limitation of drought on the growth of C. korshinskii. Moreover, the initial planting density should be tailored to local precipitation conditions (below 5,000 shrubs per hectare). The above results have important practical significance for the maintenance of the stability and sustainable management of plantation forests in the western Loess Plateau.

Spatial–Temporal Changes and Driving Force Analysis of Ecosystems in the Loess Plateau Ecological Screen

The ecological degradation caused by unreasonable development and prolonged utilization threatens economic development. In response to the development crisis triggered by ecological degradation, the Chinese government launched the National Barrier Zone (NBZ) Construction Program in 2006. However, few in-depth studies on the Loess Plateau Ecological Screen (LPES) have been conducted since the implementation of that program. To address this omission, based on the remote sensing image as the primary data, combined with meteorological, soil, hydrological, social, and economic data, and using GIS spatial analysis technology, this paper analyzes the change characteristics of the ecosystem pattern, quality, and dominant services of the ecosystem in the LPES from 2005 to 2015. The results show that from 2005 to 2015, the ecosystem structure in the study area was relatively stable, and the area of each ecosystem fluctuated slightly. However, the evaluation results based on FVC, LAI, and NPP showed that the quality of the ecosystem improved. The vegetation coverage (FVC) increased significantly at a rate of 0.91% per year, and the net primary productivity (NPP) had increased significantly at a rate of 6.94 gC/(m2∙a) per year. The leaf area index (LAI) in more than 66% of the regions improved, but there were still about 8% of the local regions that were degraded. During these 10 years, the soil erosion situation in LPES improved overall, and the amount of soil conservation (ASC) of the ecosystem in the LPES increased by about 0.18 billion tons. Grassland and forest played important roles in soil conservation in this area. Pearson correlation analysis and redundancy analysis showed that the soil conservation services (SCS) in the LPES were mainly affected by climate change, economic development, and urban construction. The precipitation (P), total solar radiation (SOL), and temperature (T) can explain 52%, 30.1%, and 17% of the change trends of SCS, respectively. Construction land and primary industry were negatively correlated with SCS, accounting for 22% and 8% of the change trends, respectively. Overall, from 2005 to 2015, the ecological environment of LPES showed a gradual improvement trend, but the phenomenon of destroying grass and forests and reclaiming wasteland still existed.

Degradation shifts plant communities from S- to R-strategy in an alpine meadow, Tibetan Plateau

The replacement of dominant sedges/grasses with secondary forbs is common in alpine rangelands, but the underlying plant ecological strategies and their relevance to leaf traits and their variabilities of different plant functional groups remain largely unknown. Here, we measured key leaf traits and analyzed the competitor, stress-tolerator and ruderal (CSR) strategies of major species with different functional groups (sedges, grasses and forbs) in an alpine meadow along a degradation gradient on the Tibetan Plateau. Our results indicated that S-selected species were dominant in both non-degraded (C:S:R = 1:95:4%) and severely degraded (C:S:R = 2:87:11%) meadows. However, there was a shift from S- to R-strategy in the communities after rangeland degradation. More specifically, sedges and grasses with a "conservative" strategy maintained stronger S-strategy to tolerate degraded and stressful conditions. In contrast, forbs with an "opportunistic" strategy (increase 9.5% in R-score) tended to adapt to degraded stages. Moreover, 51.1% and 23.9% of the increased R-scores in forbs were accounted by leaf mass per area and specific leaf area, respectively. Generally, higher leaf water and nitrogen contents coupled with larger variations in leaf traits and flexible SR strategies in forbs enabled them to capitalize on lower soil water and nutrient availability. Our findings highlighted that the contrasting strategies of plant species in response to the decrease in available resources might lead to niche expansion of secondary forbs and loss of diversity in the degraded alpine meadow. The emerging alternative stable states in the degraded rangelands might bring about a predicament for rangeland restoration.

Identifying the spatial disparities and determinants of ecosystem service balance and their implications on land use optimization

Ecosystem services (ESs) are increasingly affected by human interventions, and the ES balance between supply and demand plays a vital role in guaranteeing the expected efficacy of ecosystem restoration projects. However, the spatial disparities of ES balance, along with its determinants and spillover effects, remain unclear, constraining effective ES management and landscape planning. The aim of this study was to fill these gaps by quantifying the ES balance in the restoring Loess Plateau using an expert-based ES matrix approach and by examining the spatial associations between ES balance and driving factors via an integrated regression approach. The results showed that the county-scale ES balance was closely related to the land-use composition and population density. Geographic locations of counties with ES surplus were mainly concentrated in mountainous areas with high proportions of woodland and grassland, while urbanized land and a high population density resulted in an ES deficit. Forest and grass regeneration, due to revegetation practices, alleviated ES deficits, while rapid urbanization and population growth aggravated ES imbalance. The integrated regression approach demonstrated that the ES balance and its dependencies (i.e., landscape metrics and population density) had remarkable spatial heterogeneity and spillover effects, which should be practically considered in localized ES management and landscape optimization. Excessive agricultural reclamation and urban expansion improved grain productivity and economic profits but deteriorated landscape fragmentation, further aggravating the ES deficit. In contrast, excessive revegetation practices promoted ecosystem restoration and improved ES surplus but threatened food security. Therefore, an appropriate balanced state should be maintained for sustainable ecosystem restoration through timely and efficient policy interventions and landscape optimization.

Assessing previous land-vegetation productivity relationships on mountainous areas hosting coming Winter Olympics Games in 2022

In order to prevent land degradation in areas before hosting big events such as the Winter Olympic Games (WOG), developing strategic vegetation restoration plans is key. To evaluate four experimental areas with different degrees of human impacts located in the Chongli District, northern Hebei Province, China, where the coming WOG 2022 will take considering: i) the feedback mechanisms between vegetation and soil in the process of future vegetation restoration; ii) the vegetation productivity of land in different land-use types; iii) the management mode considering the sustainable development as the primary goal. To achieve these goals, we applied a minimum soil data set (MDS) to screen the most relevant indicators (soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), available phosphorus (AP), available potassium (AK), available nitrogen (AN), soil bulk density (BD), soil porosity (SP), pH, clay, silt, sand and gravel), and the nonlinear scoring method to establish a soil quality index (SQI). For this purpose, 400 soil samples (0-20 cm depth), the total biomass of one natural grassland (NG) and abandoned farmland (AF), and the growing stock of natural secondary forest (NF) and a larch plantation (LP). The results showed that the SQI can be established based on TN, silt, TP and gravel. Under LP and AF land-use type, vegetation showing a poor effect on the improvement of soil quality (SQIs were significantly lower than the NF and NG). It was also observed that above 1700 m, the growing stock of artificial vegetation exceeds the range of vegetation productivity (about 165 m³·h^-1) that the land can carry under the LP. We concluded that the main reason is the excessive depletion of N and P after human impacts. On the other hand, the SQI of NF and NG were higher, which is due to the significant improvement of soil quality by the conservation of the vegetation, so that no longer limited by the spatial distribution law, also showing higher vegetation productivity of land at different altitudes. This demonstrates that it is key to develop effective restoration plans considering the soil-vegetation relationship status of the NF and NG land-use types in this area in the territories used by the activities of the WOG 2022.

Quantitative Contributions of Climate Change and Human Activities to Vegetation Changes in the Upper White Nile River

Vegetation changes in the Upper White Nile River (UWNR) are of great significance to the maintenance of local livelihoods, the survival of wildlife, and the protection of species habitats. Based on the GIMMS NDVI3g and MODIS normalized difference vegetation index (NDVI) data, the temporal and spatial characteristics of vegetation changes in the UWNR from 1982 to 2020 were analyzed by a Theil-Sen median trend analysis and Mann-Kendall test. The future trend of vegetation was analyzed by the Hurst exponential method. A partial correlation analysis was used to analyze the relationship of the vegetation and climate factors, and a residual trend analysis was used to quantify the influence of climate change and human activities on vegetation change. The results indicated that the average NDVI value (0.75) of the UWNR from 1982 to 2020 was relatively high. The average coefficient of variation for the NDVI was 0.059, and the vegetation change was relatively stable. The vegetation in the UWNR increased 0.013/10 year on average, but the vegetation degradation in some areas was serious and mainly classified as agricultural land. The results of a future trend analysis showed that the vegetation in the UWNR is mainly negatively sustainable, and 62.54% of the vegetation will degrade in the future. The NDVI of the UWNR was more affected by temperature than by precipitation, especially on agricultural land and forestland, which were more negatively affected by warming. Climate change and human activities have an impact on vegetation changes, but the spatial distributions of the effects differ. The relative impact of human activities on vegetation change accounted for 64.5%, which was higher than that of climate change (35.5%). Human activities, such as the large proportion of agriculture, rapid population growth and the rapid development of urbanization were the main driving forces. Establishing a cross-border drought joint early warning mechanism, strengthening basic agricultural research, and changing traditional agricultural farming patterns may be effective measures to address food security and climate change and improve vegetation in the UWNR.

Impact of thermal condition on vegetation feedback under greening trend of China

In China, an unambiguous greening trend was observed over the last three decades. The feedback induced by vegetation growth can affect regional climate. Here, we investigated how vegetation feeds back to land surface temperature (LST) in temperature zones and land-use types in China using 18-years (2001-2018) of Moderate Resolution Imaging Spectroradiometer (MODIS) LST and Normalized Difference Vegetation Index (NDVI) data. We first showed that vegetation feedback was significantly negative (p < 0.1, t-test) in most parts of China. Specifically, we discovered a downtrend of vegetation feedback from the coldest temperature zone to the hottest temperature zone. Moreover, vegetation feedback and thermal condition showed an inverse relationship among temperature zones. The inverse relationship clarified that vegetation growth can cool most parts of China during climate change. In the end, we showed the pattern of vegetation feedback among land-use types. Due to the expansion of grassland, vegetation feedback may temporarily positive. Suitable vegetation coverage in urban land, banning deforestation, and cultivating land reasonably can decrease the local temperature by inducing negative vegetation feedback.

Associated soil aggregate nutrients and controlling factors on aggregate stability in semiarid grassland under different grazing prohibition timeframes

Grazing prohibition is an effective measure in improving soil stability and ecological quality. However, only a limited number of studies have been published on the dominant factors that impact soil aggregate stability and their associated effects on nutrient distribution for different size soil aggregates under long-term grazing prohibition management. In this study, we investigated variation in soil aggregate stability and nutrient distribution characteristics in semiarid grassland sites under different grazing prohibition timeframes (0 years [GP0], 11 years [GP11], 26 years [GP26], and 36 years [GP36]). Results showed that organic carbon (C) and total nitrogen (TN) concentrations in soil aggregates decreased at GP11 before progressively increasing and reaching its highest value at GP36, and the total phosphorus (TP) concentration did not change significantly. Most nutrients accumulated in macroaggregates (> 0.25 mm) under grazing prohibition, and the nutrient stoichiometry in soil aggregates increased after 26 years. Compared to the control (GP0), the mean weight diameter (MWD) value of the soil stability index increased at GP11 (21.7%) and decreased at GP26 (18.9%). Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) also showed that the proportion of stable organic C-related functional groups (i.e., alkene-C and aromatic-C) in macroaggregates were higher at GP11 and GP36 than at GP26. Furthermore, principal component analysis (PCA), partial least squares path modeling (PLS-PM), and the relative importance of regressors all showed that glomalin-related soil proteins (GRSP) and nutrients indirectly improved aggregate stability in semiarid grassland through their influence on the GRSP accumulation potential and nutrient stoichiometry. Generally, after 26 years grazing prohibition had a positive effect on soil aggregate stability and nutrient accumulation in the semiarid grassland sites investigated for this study. Results from this study provide a theoretical basis to select appropriate grazing prohibition timeframes under grassland management initiatives to optimize ecological quality measures in semiarid regions.

Win-win-win pathway for ecological restoration by balancing hydrological, ecological, and agricultural dimensions: Contrasting lessons from highly eroded agroforestry

Ecological restoration projects (ERP) can effectively reverse ecosystem degradation. However, some ERPs have failed to restore ecosystems under environmental constraints, and they were unable to achieve the desired ecological and economic benefits. To achieve a win-win-win target that balances the hydrological, ecological, and agricultural dimensions, we introduced the contrasting lessons from hotspots of ecosystem restoration in the arid Loess Plateau (LP) and the humid Karst Plateau (KP) in China, and discussed a novel strategy for coordinating ecosystem restoration, water and food security, and residents' livelihoods. The biophysical models and related statistical records showed that aggressive ERPs and soil and water conservation projects (SWCPs) significantly promoted vegetation restoration and reduced soil erosion and sediment yield in both areas. However, excessive afforestation in the arid LP exhausted water resources and threatened ecosystem sustainability. The accelerated replacement of cropland since 1999 in the LP aggravated cropland shortage which led to carbon sequestration and grain productivity declines in the initial years. However, the construction of terrace and check-dam fields and improvements in the conditions of agricultural production reconciled the cropland shortage and stabilized food security. The positive involvement of stakeholders in ERPs effectively minimized land degradation through economic development and the improved livelihoods of local residents. Therefore, based on the evidence from the KP and LP, the proposed win-win-win strategy is potentially applicable in other global regions that suffer from land degradation. This strategy can achieve considerable success if the planners have a good understanding of local environmental conditions as well as the social and economic needs of residents affected by ERPs.

Rare prokaryotic sub-communities dominate the complexity of ecological networks and soil multinutrient cycling during long-term secondary succession in China's Loess Plateau

Unraveling the succession of microbial communities is a core ecological research topic. Yet few studies have focused on how long-term secondary succession affects the functional profiles and ecological processes of abundant and rare microbial subcommunities. Here, we used amplicon sequencing and GeoChip analysis to explore the ecological functions of abundant and rare biospheres and their correlation with soil multinutrient cycling. Samples for this study were collected from a well-established secondary succession chronosequence that spans >30 years of dryland ecosystem development on the Loess Plateau of China. Although both abundant and rare subcommunities shifted with succession, the changing of beta-diversity of the microbial communities was primarily driven by species replacement of the rare biosphere. Phylogenetic changes of abundant and rare taxa were associated with their functional traits, which dominated the diversity-related selection along all succession ages. Neutral theory analysis indicated that the assemblage of abundant taxa over all successional ages was regulated by dispersal homogenizing and ecological drift. The null model revealed that homogeneous and variable selection were the dominant assembly processes for rare subcommunities compared with abundant species. pH and nitrogen content were the paramount drivers determining the assembly of microbial communities and functional genes, consistent with the importance of environmental filtering. Furthermore, the rare biosphere had a paramount role in the entire ecological network and was the major driver for most soil processes such as C, N, and S cycling. Nonetheless, a significant portion of soil P cycling was regulated by abundant taxa. Collectively, our study provides insight into the mechanisms underlying microbial community assembly and soil microbe-driven functional changes in biogeochemical processes during secondary succession.

Quantitative Analysis of Factors Influencing Spatial Distribution of Soil Erosion Based on Geo-Detector Model under Diverse Geomorphological Types

The Loess Plateau of China suffers from severe erosion, which results in a great variety of economic and ecological problems. For scientific control of soil erosion, the key questions urgently to be addressed in this paper are: (1) Which are the driving factors under diverse geomorphological types? (2) Do these driving factors operate independently or by interacting? (3) Which zones under diverse geomorphological types suffer from severe erosion and need more attention? In this paper, the RUSLE model was applied here to demonstrate the spatio-temporal variations in soil erosion from 2010 to 2017 in Yan’an City, and the Geo-detector model proved to be a useful tool to solve the questions mentioned above. The results showed that the average erosion modulus in Yan’an City decreased by 1927.36 t/km2·a from 2010 to 2017. The intensity of soil erosion in the northern Baota District, central Ganquan County, Luochuan County, Ansai County, and Zhidan County decreased to varying degrees. The effect size of driving factors affecting soil erosion varied significantly in diverse geomorphological types. The effect size of interaction between land-use types and vegetation coverage, land-use types and slope, slope and precipitation was higher than that of a single factor. High-risk zones with severe erosion were closer to cultivated land and forest land with steep slopes (>25°) in the mid-elevation hills of Yan’an City. Additionally, based on the specificity of the study area, the Geo-detector model performed better in a relatively flat region, and factors with macroscopic spatial distributions weaken its explanatory power on soil erosion on a regional scale. Based on data selection, data of different accuracy sparked the issue of “data coupling”, which led to the enormous deviation of model results in mid-elevation plains. Results from our analysis provide insights for a more ecologically sound development of Yan’an City and provide references for the scientific use of the Geo-detector model.

Effects of long-term afforestation and natural grassland recovery on soil properties and quality in Loess Plateau (China)

Long-term afforestation has important implications on soil properties and quality in semi-arid areas. A large-scale afforestation project has been carried out in the Loess Plateau in the last 20 years. This work aims to study the afforestation (Robinia pseudoacacia, Caragana korshinskii and natural grassland recover 10, 20, 30, and 40 years after) impacts on soil properties and quality. The results showed that coverage and root biomass (RB) was the highest 30 years after the restoration in Robinia pseudoacacia and Caragana korshinskii treatments, while the highest 40 years post-restoration in natural grasslands. Sand content and BD showed the highest values 10 years post afforestation in all study areas. Clay, Silt, mean weight diameter (MWD), and geometric mean diameter (GMD) in Robinia pseudoacacia, Caragana korshinskii had the highest values 30 years after the afforestation, while in natural grasslands, this was observed 40 years after. In Robinia pseudoacacia, Caragana korshinskii treatments, soil moisture content (SMC) reached the highest levels 30 years post afforestation at 20-40 and 40-60 cm. Regarding natural grasslands, SMC had the highest values 40 years post-afforestation. Sand content and BD increased with soil depth, while the opposite was identified in RB, clay, silt, MWD, GMD and SMC. In Robinia pseudoacacia and Caragana korshinskii treatments, soil organic matter, total nitrogen, available nitrogen, total phosphorous, and available phosphorus had the highest levels 40 years post-restoration at 0-20 cm, while at 20-40 and 40-60 cm, the highest concentrations were identified 30 years after. In all the treatments, the soil quality index (SQI) was the highest 40 years post-restoration. The values of SQI were always higher in natural grasslands than in Robinia pseudoacacia and Caragana korshinskii treatments. Overall, natural recovery (natural grasslands) is more efficient than afforestation (Robinia pseudoacacia and Caragana korshinskii treatments) in soil quality.

Spatiotemporal variation of nitrogen and phosphorus and its main influencing factors in Huangshui River basin

The foundation of managing excess nutrients in river is the identification of key physical processes and the control of decisive influencing factors. The existing studies seldom consider the influence of rainfall-runoff relationship and only focus on a few anthropogenic activities and natural attributes factors. To address this issue, a comprehensive set of influencing factors including rainfall-runoff relationship (represented by runoff coefficient), basic physical and chemical parameters of water quality, land use types, landscape patterns, topography, and socioeconomic development was constructed in this study. M-K test and cluster analysis were conducted to identify the temporal mutation and spatial clustering characteristics of NH₃-N and TP in Huangshui River basin, respectively. Partial least squares regression was used to elucidate the linkages between water contaminants and the factors. As shown in the results, the temporal mutations of NH₃-N and TP were obvious in the middle reaches, with 4 out of 7 catchments in the middle reaches have a larger number of mutations of NH₃-N than other catchments. The cluster analysis results of NH₃-N and TP among catchments were similar. This study also indicated that although the Huangshui River basin was located in the upper reaches of the Yellow River, the influences of rainfall-runoff relationship on spatiotemporal changes of NH₃-N and TP in its sub-basins were limited. Only the temporal change of NH₃-N in Jintan catchment in the upstream area was significantly affected by runoff coefficient. The indexes of proportion of water area (PWA), proportion of impervious area (PIA), and proportion of primary industry (PPI) were the top three influencing factors of temporal variation of NH₃-N and TP for most catchments in the middle reaches. The temporal change of NH₃-N in Jintan catchment in the upstream area was obviously affected by runoff coefficient. The spatial variation of NH₃-N and TP were all affected by PWA and proportion of secondary industry significantly. The results of this study can provide theoretical basis and technical support for the control and management of nitrogen and phosphorus pollution in upper reaches of rivers.

Climate change versus land-use change-What affects the ecosystem services more in the forest-steppe ecotone?

The Ecosystem services (ESs), which play an important role in the balance of the natural ecosystem and social-economic development, are suffering from degradation caused by human activities and climate change. However, the manner in which the ESs respond to the land use/cover changes (LUCCs) and the climatic factors respectively remain elusive, especially in the forest-steppe ecotone, which is highly sensitive to climate change and anthroponotic activities. Based on the remote sensing data and in situ meteorological data, we comprehensively modeled and compared 4 key ESs changes caused by 3 LUCC types, land-use change fraction, and climate changes through two simple comparative experiments. Our results showed that: the Grain for the Green Project improved the mean soil conservation, carbon sequestration, and water yield but reduced the sand fixation. The cropland expansion had a positive influence on the water yield and sand fixation, but it induced a decline in soil conservation and carbon sequestration. The urbanization very likely increased the water yield and decreased soil conservation, carbon sequestration, and sand fixation. The unequal change fractions of the same land-use conversion may affect the ESs differently. The ESs changes have different responses to climate change in different landscapes due to the ecological process. The water yield could be well explained by the temperature, precipitation, radiation, and wind speed. Climate change had a stronger effect on the water yield and carbon sequestration than the land use/cover changes but sand fixation and soil conservation were more likely to be affected by LUCCs. The impact of three types of land-use changes and climate change on the ecosystem services should be considered when formulating land-use policies. This paper might aid the decision-makers in achieving ESs sustainable management and develop land-use strategies in the forest-steppe ecotone.

Towards the progress of ecological restoration and economic development in China's Loess Plateau and strategy for more sustainable development

China's Loess Plateau (LP) is one of the most typical regions with serious soil erosion. Its ecological restoration, economic development, and social progress are directly related to realizing China's national sustainable development goals (SDGs). With intensive field investigations, comprehensive analyses of statistical data, remote sensing data, and local monitoring data, this current research explored the achievements in local ecological restoration and economic development, discussed the main problems faced by the LP, and assessed the sustainable development status of the LP. Moreover, drawing from a 3C system approach (classification-coordination-collaboration), this research proposed the sustainable development strategies for more sustainable LP. We found that the LP's ecological restoration and economic development made remarkable achievements since 2000. However, the environment was still fragile and regional development was still lagging behind. In realizing SDGs, further improvements on clean water and sanitation, decent work and economic growth, industry, innovation and infrastructure, reduced inequalities, and climate action are needed. Coordinated and collaborated efforts are expected from multiple hierarchical levels including household, watershed, region, and nation in developing LP. Specifically, human-environment interactions should be highlighted at the household level, upstream-downstream interactions that are catering to the particular characteristics of the LP is encouraged at the watershed level, and regional and urban-rural interactions shall play an increasingly important role at the regional level. While at the national level, the central government should carry out a systematic overarching design. To better realize the goal of more sustainable LP, this research calls for (1) forming an actor-network consists of multi stakeholders, including the central government, local government, watershed, families, ecosystem and environment, enterprises, NGOs, and scientists, and (2) paying attention to ecosystem management, ecological restoration, industrial structure optimization, ecological agriculture, rural infrastructure, and ecological civilization construction in the future development.

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.

Sensitivity and future exposure of ecosystem services to climate change on the Tibetan Plateau of China

CONTEXT

Climate change has imposed tremendous impacts on ecosystem services. Recent attempts to quantify such impacts mainly focused on a basin or larger scale, or used limited time periods that largely ignore observations of long-term trends at a fine resolution, thereby affecting the recognition of climate change's effect on ecosystem services.

OBJECTIVES

This study conducts a detailed and spatially explicit recognition of climate change's effect on ecosystem services and provides an intuitive map for decision-making and climate change adaptation planning.

METHODS

We used long-term time series of ecosystem service assessments and various future climate scenarios to quantify the sensitivity and future exposure of ecosystem services to climate change on the Tibetan Plateau.

RESULTS

Carbon sequestration (CS) and habitat quality experience significant growth, while water retention did not show any trend. Sensitivity patterns of these ecosystem services vary largely. For CS, more than half of the pixels showed a positive sensitivity to climate change, even though the degree of sensitivity is not high. There is substantial spatial heterogeneity in the exposure of ecosystem services to future climate changes, and high levels of future climate change increase the intensity of exposure.

CONCLUSIONS

This study illustrates the complex spatial association between ecosystem services and climatic drivers, and these findings can help optimize local response strategies in the context of global warming. For example, the existing protected areas have notable conservation gaps for disturbance of future climate change on ecosystem services, especially in the southeastern part of the study area.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10980-021-01320-9.

Spatial–Temporal Characteristics and Influencing Factors of Coupled Coordination between Urbanization and Eco-Environment: A Case Study of 13 Urban Agglomerations in China

Urban agglomeration is the core area of not only regional economic development and urbanization but also human–land contradiction. Based on the population–economy–society–spatial model and the pressure–state–response model, this study develops an evaluation index system for the urbanization and eco-environment of 13 urban agglomerations in China. The urbanization index and eco-environment index are determined using the coefficient of variation method. The coupled coordination of the two indices is measured with the coupled coordination model, and the influence of the indicator factors is calculated with a geographical detector. The results reveal the following: (1) The urbanization indices of the 13 urban agglomerations in China increase year by year, and the spatial distribution pattern is high in the east and low in the west. (2) The eco-environment index shows an “S-shaped” variation trend, and the spatial difference between urban agglomerations gradually decreases. (3) The coupled coordination is mainly characterized as a mild imbalance, and the spatial distribution pattern is “balance in the east and imbalance in the west”. (4) The coupled coordination degree between urbanization and eco-environment is affected by many factors. Among such factors, economic urbanization, social urbanization, spatial urbanization, and eco-environment response are the main controlling factors. The impact of population urbanization, eco-environment pressure, and eco-environment state presents a gradual increase.