Soil microbial community and their functional genes during grassland restoration

Cadmium and pyrene in the soil modify the properties of earthworm-mediated soil

Earthworms are pivotal in soil ecosystems due to their crucial role in shaping soil characteristics through casts and burrow walls. Previous research has predominantly focused on the direct impact of soil pollution on live earthworms, overlooking the subsequent effects on earthworm-mediated soil, such as casts and burrow walls. Using 2D-terraria as incubation containers and the geophagous earthworm species Metaphire guillelmi, this study assessed the change in various properties of earthworm-mediated soil in both uncontaminated soils and Cd- and Pye-contaminated soils. Overall, both Cd and Pye overall improved the ammonium nitrogen (NH4+-N), Olsen's phosphorus (Olsen-P) levels, and invertase and catalase activities while decreasing catalase activities in earthworm-mediated soil. They also fluctuating affected the pH, soil organic matter (SOM) content, soil urease, alkaline phosphatase activities, and microbial functional genes in the cast and burrow walls. These results indicated that earthworms remained crucial "ecosystem engineers" even in polluted soil. Additionally, differences were observed in the responses of properties between casts and burrow walls, showing unequal contributions of transit-through-gut and burrowing processes to soil modification. Specifically, transit-through-gut was found to have a more significant influence on soil NH4+-N and Olsen-P content compared to burrowing behavior. Regarding the pattern of microbial functional genes in earthworm-associated compartments, results revealed that they differed significantly in casts from those in bulk soil and burrow walls under unpolluted conditions, with pollution-enhancing disparities among compartments. Furthermore, NH4+-N and Olsen-P content, urease, and catalase activities in burrow walls and/or casts were identified as potential biomarkers for soil pollution, exhibiting a clear dose-effect relationship. Developing such biomarkers could address ethical concerns related to conventional earthworm biomarkers that require sacrificing earthworms. This study provides insights into the consequences of soil pollution on earthworm-mediated soil components, highlighting the importance of considering the indirect effects of contaminants on soil ecosystems.

Effects of salt stress on the rhizosphere soil microbial communities of Suaeda salsa (L.) Pall. in the Yellow River Delta

Studies have shown that the microbiome of saline-tolerant plants plays a significant role in promoting salt stress in non-saline-tolerant plants, but the microorganisms are still unclear. In the present study, the microbial diversity changes in Suaeda salsa (L.) Pall. in the Yellow River Delta region were investigated. In the bacterial community, the dominant bacteria in the rhizosphere soil of the low-saline soil (YDL), moderate-saline soil (YDM), and high-saline soil (YDH) groups were Proteobacteria, Chloroflexi, Bacteroidota, and Actinobacteriota (at the phylum level), while Ascomycota and Basidiomycota were the dominant fungi in the fungal community. At the family level, with the increase of salinity, the relative abundance of Rhodobacteraceae (bacterial community), Thermoascaceae, and Phaffomycetaceae (fungal community) gradually increased; and to the best of our knowledge, there are no reports on the relationship between Thermoascaceae and Phaffomycetaceae families with salt stress. At the genus level, Salinimicrobium (bacterial community) was the dominant bacterium in the rhizosphere soil of the YDL, YDM, and YDH groups, while with the increase of salinity, the relative abundance of Byssochlamys and Wickerhamomyces (fungal community) gradually increased, and to the best of our knowledge there are no reports on the relationship between Byssochlamys and salt stress. Salinity mainly affected the bacterial community abundance, but it had little effect on the fungi community abundance. The bacterial community of the YDH group was dominated by bacteria of unknown origin (52.76%), while bacteria of unknown origin accounted for 26.46% and 20.78% of the bacterial communities in the YDM and YDL groups, respectively. The fungi community of the YDH group was dominated by YDL group fungi (relative abundance of 44.44%), followed by YDM group fungi (29.42%) and fungi of unknown origin (26.14%). These results provide a better understanding of the rhizosphere microbial diversity of saline-alkali-tolerant plants, laying a foundation for developing a saline-alkali-tolerant plant microbiome.

The Response of Rhizosphere Microbial C and N-Cycling Gene Abundance of Sand-Fixing Shrub to Stand Age Following Desert Restoration

Rhizosphere microorganisms play a pivotal role in biogeochemical cycles, particularly in relation to carbon (C) and nitrogen (N) cycles. However, the impact of stand age on the composition of rhizosphere microbial communities and the abundance involved in C and N cycling remains largely unexplored in restoration ecosystems dominated by shrubs of temperate deserts. This study focuses on revealing changes in microbial composition and functional genes in the rhizosphere soil of Caragana korshinskii after revegetation, as well as their response mechanisms to changes in environmental factors. The alpha diversity of bacteria tended to increase with stand age, whereas that of fungi decreased. The abundance of denitrification; dissimilatory nitrate reduction to ammonium, nitrification, and ammonium assimilation; and C fixation-related gene levels increased with stand age, whereas those related to the degradation of starch, pectin, hemicellulose, cellulose, and aromatics decreased. The parameters MBC, MBN, and TC were the key factors affecting the bacterial community, whereas the fungal community was regulated by TN, EC, pH, and MBC. Stand age indirectly regulated C and N cycling functions of genes through altered soil properties and microbial community structures. This study presents a novel approach to accurately evaluate the C and N cycling dynamics within ecosystems at various stages of restoration.

Plants Restoration Drives the Gobi Soil Microbial Diversity for Improving Soil Quality

Desertification and salt stress are major causes of terrestrial ecosystem loss worldwide, and the Gobi, representing a salt-stressed area in inland China, has a major impact on the ecosystems and biodiversity of its surrounding environment. The restoration of the Gobi Desert is an important way to control its expansion, but there are few studies on the evaluation of restoration. In this study, soils under different restoration scenarios, namely, soils in restored areas (R1, R2), semi-restored areas (SR1, SR2), and unrestored control areas (C1, C2), were used to investigate differences in microbial diversity and physicochemical properties. The results showed that the soil was mainly dominated by particles of 4-63 μm (26.45-37.94%) and >63 μm (57.95-72.87%). Across the different restoration levels, the soil pH (7.96-8.43) remained basically unchanged, salinity decreased from 9.23-2.26 to 0.24-0.25, and water content remained constant (10.98-12.27%) except for one restored sample in which it was higher (22.32%). The effective Al, Cu, and Zn in the soil increased, but only slightly. Total organic matter (TOM) decreased from 3.86-5.20% to 1.31-1.47%, and total organic nitrogen (TON) decreased from 0.03-0.06% to 0.01-0.02%, but the difference in total organic carbon (TOC) was not significant. High-throughput testing revealed that the bacterial population of the restored area was dominated by A4b (6.33-9.18%), MND1 (4.94-7.39%), and Vicinamibacteraceae (7.04-7.39%). Regarding archaea, samples from the restored areas were dominated by Marine Group II (76.17-81.49%) and Candidatus Nitrososphaera (6.07-9.75%). PCoA showed that the different restoration levels were the main cause of the differences between the samples. Additionally, salinity was the dominant factor that induced this difference, but it was inhibited by the restoration and targeted enrichment of some of these functional genera. Desert restoration should therefore focus on conserving water rather than adding nutrients. Planting salt- and drought-tolerant vegetation will contribute to the initial restoration of the desert and the restoration of the microbiological content of the soil as it migrates over time, creating a cycle of elements. Restoration stimulates and enhances the microbial diversity of the soil via beneficial microorganisms.

Artemisia smithii patches form fertile islands and lead to heterogeneity of soil bacteria and fungi within and around the patches in alpine meadows of the Qinghai-Tibetan Plateau

Herbivore-avoided plant patches are one of the initial characteristics of natural grassland degradation. These vegetation patches can intensify the spatial heterogeneity of soil nutrients within these grasslands. However, the effects of non-edible plant patches patches on the spatial heterogeneity of microorganisms have not been sufficiently studied in alpine meadows of the Qinghai-Tibetan Plateau, especially patches formed by herbaceous plants. To answer this question, soil nutrients, plant assembly, and microbial communities were measured inside, around, and outside of Artemisia smithii patches. These were 0 m (within the patch), 0-1 m (one meter from the edge of the patch), 1-2 m (two meters from the edge of the patch), 2-3 m (three meters from the edge of the patch), and >30 m (non-patch grassland more than thirty meters from the edge of the patch). Our results showed that A. smithii patches accumulated more aboveground biomass (AGB) within the patches (0 m), and formed fertile islands with the soil around the patches. Additionally, A. smithii patches increased soil bacterial diversity within (0 m) and around (0-1 m) the patches by primarily enriching copiotrophic bacteria (Actinobacteria), while the diversity of fungal communities increased mainly in the 0-1 m area but not within the patches. Bacterial community diversity was driven by pH, urease, nitrate nitrogen (NO3 --N), and microbial biomass carbon (MBC). The contents of soil water (SWC), soil organic matter (SOM), urease, NO3 --N, and MBC were the main factors influencing the diversity of the fungal community. This study elucidates the vegetation, nutrients, and microbial heterogeneity and their interrelationships, which are observed in fertile islands of herbivore-avoided plant patches in alpine meadows, and provides further insights into the spatial pattern of nutrients in patchy degraded grasslands.

Long-term vegetation restoration promotes lignin phenol preservation and microbial anabolism in forest plantations: Implications for soil organic carbon dynamics

Vegetation restoration contributes to soil organic carbon (C; SOC) sequestration through the accumulation of plant and microbial residues, but the mechanisms underlying this microbially mediated process are not well resolved. To depict the dynamics of plant- and microbial-derived C in restored forest ecosystems, soil samples were collected from Robinia pseudoacacia plantations of different stand ages (15, 25, 35, 45 years old) established on degraded wheat fields. The results showed that the degree of lignin phenol oxidation decreased with increasing stand age (P < 0.05), and hemicellulose-degrading genes were detected at higher relative abundances than other functional gene categories, indicating selective preservation of recalcitrant lignin phenols. Despite both glucosamine (R2 = 0.61, P < 0.001) and muramic acid (R2 = 0.37, P < 0.001) contents trending upward over time, fungal residual C accounted for a greater proportion of SOC compared with bacterial residual C. Accordingly, fungal residual C, which exhibited a similar response pattern as total microbial residual C to vegetation restoration, was considered a major contributor to the SOC pool. These results provided evidence that long-term vegetation restoration enhanced SOC sequestration in R. pseudoacacia forest by promoting the preservation of plant-derived lignin phenols and concomitant microbial anabolism. Partial least squares-discriminant analysis identified two important ecological clusters (i.e., modules) in the fungal network that profoundly influenced lignin phenol oxidation (P < 0.05) and microbial residual C accumulation (P < 0.01). Among the dominant taxa in microbial networks, the bacterial phyla Proteobacteria and Acidobacteriota had potential to degrade recalcitrant C compounds (e.g., cellulose, lignin), whereas the fungal phylum Ascomycota could outcompete for labile C fractions (e.g., dissolved organic C). Findings of this study can enable a mechanistic understanding of SOC stability driven by microbial turnover in restored forest ecosystems.

Vegetation restoration in an alpine meadow: Insights from soil microbial communities and resource limitation across soil depth

Aboveground vegetation restoration shapes the soil microbial community structure and affects microbial resource acquisition. However, the changes in soil microbial resource limitation in subsoil during vegetation restoration are still unclear. In this study, the microbial community structure and resource limitation in an alpine meadow soil profile that had undergone natural restoration for short-term (4-year) and long-term (10-year) restoration in response to vegetation restoration were explored through high-throughput sequencing analysis and extracellular enzyme stoichiometry (EES). There was no significant difference in microbial composition and α diversity between short- and long-term restoration soils. Soil microorganisms in this alpine meadow were mainly limited by phosphorus. Carbon limitation of soil microorganisms was significantly decreased in each layer (0-15, 15-30, 30-45, 45-60, and 60-80 cm corresponding to L1, L2, L3, L4, and L5, respectively) of long-term restoration soils when compared to that of the short-term restoration soil layers, while phosphorus limitation of microorganisms in subsoil (60-80 cm) was significantly increased by 17.38%. Soil nutrients, pH, moisture content, and microbial composition are the main drivers of microbial resource limitation in restoration, and their effects on microbial resource limitation were different in short- and long-term restoration. Meanwhile, key microbial taxa have a significant impact on microbial resource limitation, especially in short-term restoration soils. This study suggested that vegetation restoration significantly affected soil microbial resource limitation, and could alleviate microbial resource limitations by adding nutrients, thus accelerating the process of vegetation restoration in alpine ecosystems.

Synthetic Microbial Community Promotes Bacterial Communities Leading to Soil Multifunctionality in Desertified Land

Soil desertification is an important challenge in global soil management, and effectively and stably restoring soil function is an urgent problem. Using synthetic microbial communities (SynComs) is a burgeoning microbial strategy aimed at enhancing soil nutrients through functional synergies among diverse microorganisms; nevertheless, their effectiveness in restoring desertified soils remains unknown. In this study, we conducted a two-year field experiment using a SynCom constructed by in situ probiotic bacteria and set up control, chemical fertilizer, and combined SynCom-chemical fertilizer (combined fertilizer) treatments to investigate the linkage between microbial communities and soil multifunctionality in the soil surface layer (0-10 cm). Both the bacterial and fungal communities differed the most under the combined fertilizer treatment compared to the control. The bacterial communities differed more under treatments of the SynCom than the chemical fertilizer, while the fungal communities differed more under the chemical fertilizer treatment than the SynCom treatment. Regarding soil function, the SynCom strengthened the correlation between enzyme activities and both bacterial communities and functional properties. pH and available potassium were the main influencing factors under the chemical fertilizer and combined fertilizer treatments. The beta-diversity of the bacterial communities was significantly correlated with soil multifunctionality. Random forest analyses showed that the SynCom significantly enhanced the bacterial communities, driving soil multifunctionality, and that some potential microbial taxa drove multiple nutrient cycles simultaneously. In summary, the SynCom effectively increased the abundance of most carbon, nitrogen, and phosphorus functional genes as well as soil enzyme activities. The bacterial community composition contributed significantly to soil multifunctionality. Hence, the development of novel microbial agents holds significant potential for improving soil functionality and managing desertification.

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.

Fungal, but not bacterial, diversity and network complexity promote network stability during roadside slope restoration

To restore degraded roadside ecosystems, conventional methods such as revegetation and soil amendment are frequently employed. However, our understanding of the long-term effects of these restoration approaches on soil microbial diversity and network complexity across different vegetation types remains poor, which contributes to poor restoration outcomes. In this study, we explored the effects of roadside slope restoration on microbial communities across different vegetation types at varying stages of restoration. We found that restoration time had a more pronounced impact on microbial diversity than specific vegetation type. As restoration progressed, microbial network complexity and fungal diversity increased, but bacterial diversity declined, suggesting that keystone taxa may contribute to network complexity. Interestingly, bacterial network complexity increased concomitant with decreasing network modularity and robustness, which may compromise system stability. Distinct vegetation types were associated with restoration-sensitive microbial communities at different restoration stages. Leguminouse and nitrogen-fixing plants, such as Albiziak alkora, Ginkgo biloba, Rhus chinensis, Rhapis excels, and Rubia cordifolia exhibited such associations after five years of restoration. These keystone taxa included Proteobacteria, Actinobacteria, Chloroflexi, Gemmatimonadota, and Myxococcota. We also found that bacterial alpha diversity was significantly correlated with restoration time, soil pH, moisture, available phosphate, nitrate nitrogen, and plant height, while fungal diversity was primarily shaped by restoration time. Together, our findings suggest that soil properties, environmental factors, vegetation type, and dominant species can be manipulated to guide the trajectory of ecological recovery by regulating the abundance of certain microbial taxa.

Urea fertilization increased CO2 and CH4 emissions by enhancing C-cycling genes in semi-arid grasslands

Global climate change is predicted to increase exogenous N input into terrestrial ecosystems, leading to significant changes in soil C-cycling. However, it remains largely unknown how these changes affect soil C-cycling, especially in semi-arid grasslands, which are one of the most vulnerable ecosystems. Here, based on a 3-year field study involving N additions (0, 25, 50, and 100 kg ha-1 yr-1 of urea) in a semi-arid grassland on the Loess Plateau, we investigated the impact of urea fertilization on plant characteristics, soil properties, CO2 and CH4 emissions, and microbial C cycling genes. The compositions of genes involved in C cycling, including C fixation, degradation, methanogenesis, and methane oxidation, were determined using metagenomics analysis. We found that N enrichment increased both above- and belowground biomasses and soil organic C content, but this positive effect was weakened when excessive N was input (N100). N enrichment also altered the C-cycling processes by modifying C-cycle-related genes, specifically stimulating the Calvin cycle C-fixation process, which led to an increase in the relative abundance of cbbS, prkB, and cbbL genes. However, it had no significant effect on the Reductive citrate cycle and 3-hydroxypropionate bi-cycle. N enrichment led to higher soil CO2 and CH4 emissions compared to treatments without added N. This increase showed significant correlations with C degradation genes (bglA, per, and lpo), methanogenesis genes (mch, ftr, and mcr), methane oxidation genes (pmoA, pmoB, and pmoC), and the abundance of microbial taxa harboring these genes. Microbial C-cycling genes were primarily influenced by N-induced changes in soil properties. Specifically, reduced soil pH largely explained the alterations in methane metabolism, while elevated available N levels were mainly responsible for the shift in C fixation and C degradation genes. Our results suggest that soil N enrichment enhances microbial C-cycling processes and soil CO2 and CH4 emissions in semi-arid ecosystems, which contributes to more accurate predictions of ecosystem C-cycling under future climate change.

Molecular insight into the vertical migration and degradation of dissolved organic matter in riparian soil profiles

Due to the molecular complexity of dissolving organic matter (DOM), the vertical molecular distribution of riparian soil DOM (especially dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP)) in different land use types and their relationship with the bacterial community is still unclear. This study analyzed the spectral characteristics of riparian soil DOM from 0 to 100 cm in wild grassland, agricultural land, and bare land. The molecular distribution of DOM was revealed through Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and the specific relationship between DOM and bacterial community composition (BCC) was evaluated. The results showed that the DOM in the upper soil layer (0-40 cm) was mainly composed of recalcitrant macromolecular organics, while that in the lower layer (40-100 cm) was labile small molecular organics. In agricultural land, the total storage of DOM was lower than that in wild grassland, but with a higher abundance of recalcitrant organic carbon (lignin, etc.). At the same time, the bacterial community in agricultural land is shifting towards copiotrophs. In addition, the abundance of labile C degrading genes increases with nitrate as the main electron acceptor. However, sulfates are mainly used as electron acceptors in wild grasslands. Both DOP and DON were dominated by lignin and displayed higher chemical diversity in the upper soil. The bioavailability of DOP in three types of soil is higher than that of DON. DOM-BCC network analysis shows that the recalcitrant DON and DOP molecules in soil are positively correlated with phylum Actinobacteriota in agricultural land. These results emphasize that the DOM molecular characteristics were closely related to the function of the soil bacterial community.

Fungal community composition changes and reduced bacterial diversity drive improvements in the soil quality index during arable land restoration

Arable land is facing the growing challenge of land degradation due to intensive use and this is beginning to affect global food security. However, active and passive restoration can improve soil characteristics and reshape microbial communities. Despite the increasing focus on changes in microbial communities during restoration, the mechanisms underlying how microbes drive the soil quality index (SQI) in arable land restoration remain unclear. In this study, we selected conventional farmland (CF, heavily intensified) and two restoration strategies (AR, artificial restoration; NR, natural restoration), with the same context (including soil texture, climate, etc.), and measured the microbial indicators over 2 years to investigate the mechanisms driving SQI improvement on restored arable land. The AR and NR treatments resulted in a 50% and 58% increase in SQI, respectively, compared to CF as soil nutrient levels increased, resulting in higher microbial biomasses and enzyme activities. Microbial abundance on the AR land was approximately two times greater than on the NR land due to the introduction of legumes. Bacterial diversity declined, while fungi developed in a more diverse direction under the restoration strategies. The AR and NR areas were mainly enriched with rhizobium (Microvirga, Bradyrhizobium), which contribute to healthy plant growth. The pathogenic fungi (Gibberella, Fusarium, Volutella) were more abundant in the CF area and the plant pathogen guild was about five times higher in the restored areas. Following arable land restoration, microbial life history strategies shifted from r-to K-strategists due to the higher proportion of recalcitrant SOC (DOC/SOC decreased by 18%-30%). The altered microbial community in the restored areas created new levels of functionality, with a 2.6%-4.3% decrease in bacterial energy metabolism (oxidative phosphorylation, C fixation, and N metabolism decreased by 7%, 4%, and 6%, respectively). Structural equation modelling suggested that restoration strategy affected SQI either directly by increasing total soil nutrient levels or indirectly by altering the microbial community and that fungal community composition and bacterial diversity made the largest contributions to SQI. These results provided new insights into soil quality improvement from a microbial perspective and can help guide future arable land restoration.

Seasonal changes in N-cycling functional genes in sediments and their influencing factors in a typical eutrophic shallow lake, China

N-cycling processes mediated by microorganisms are directly linked to the eutrophication of lakes and ecosystem health. Exploring the variation and influencing factors of N-cycling-related genes is of great significance for controlling the eutrophication of lakes. However, seasonal dynamics of genomic information encoding nitrogen (N) cycling in sediments of eutrophic lakes have not yet been clearly addressed. We collected sediments in the Baiyangdian (BYD) Lake in four seasons to explore the dynamic variation of N-cycling functional genes based on a shotgun metagenome sequencing approach and to reveal their key influencing factors. Our results showed that dissimilatory nitrate reduction (DNRA), assimilatory nitrate reduction (ANRA), and denitrification were the dominant N-cycling processes, and the abundance of nirS and amoC were higher than other functional genes by at least one order of magnitude. Functional genes, such as nirS, nirK and amoC, generally showed a consistent decreasing trend from the warming season (i.e., spring, summer, fall) to the cold season (i.e., winter). Furthermore, a significantly higher abundance of nitrification functional genes (e.g., amoB, amoC and hao) in spring and denitrification functional genes (e.g., nirS, norC and nosZ) in fall were observed. N-cycling processes in four seasons were influenced by different dominant environmental factors. Generally, dissolved organic carbon (DOC) or sediment organic matter (SOM), water temperature (T) and antibiotics (e.g., Norfloxacin and ofloxacin) were significantly correlated with N-cycling processes. The findings imply that sediment organic carbon and antibiotics may be potentially key factors influencing N-cycling processes in lake ecosystems, which will provide a reference for nitrogen management in eutrophic lakes.

Magnetic biochar accelerates microbial succession and enhances assimilatory nitrate reduction during pig manure composting

Biochar promotes microbial metabolic activities and reduces N2O on aerobic composting. However, the effects of magnetic biochar (MBC) on the microbial succession and N2O emissions during pig manure composting remain unclear. Herein, a 42-day composting experiment was conducted with five treatment regimes: pig manure without biochar (CK), 5 % pig manure-based biochar (5 % PBC), 2 % MBC (2 % MBC), 5 % MBC (5 % MBC) and 7.5 % MBC (7.5 % MBC)), to clarify the variation in functional microorganisms and genes associated with nitrogen and direct interspecies electron transfer via metagenomics. Fourier-transform infrared spectroscopy showed that MBC possessed more stable aromatic structures than pig manure-based biochar (PBC), indicating its greater potential for nitrous oxide reduction. MBC treatments were more effective in composting organic matter and improving the carbon/nitrogen ratio than PBC. The microbial composition during composting varied significantly, with the dominant phyla shifting from Firmicutes to Proteobacteria, Actinobacteria, and Bacteroidota. Network and hierarchical clustering analyses showed that the MBC treatment enhanced the interactions of dominant microbes (Proteobacteria and Bacteroidota) and accelerated the composting process. The biochar addition accelerated assimilatory nitrate reduction and slowed dissimilatory nitrate reduction and denitrification. The Mantel test demonstrated that magnetic biochar potentially helped regulate composting nutrients and affected functional nitrogen genes. These findings shed light on the role of MBC in mitigating greenhouse gas emissions during aerobic composting.

Effective microorganisms input efficiently improves the vegetation and microbial community of degraded alpine grassland

Soil beneficial microorganism deficiency in the degraded grasslands have emerged as the major factors negatively impacting soil quality and vegetation productivity. EM (effective microorganisms) has been regarded as a good ameliorant in improving microbial communities and restoring degraded soil of agricultural systems. However, knowledge was inadequate regarding the effects of adding EM on the degraded alpine grassland. Four levels of EM addition (0, 150, 200, 250 mL m-2) were conducted to investigate the effects of EM addition on soil properties and microorganisms of degraded alpine grassland. The addition of EM increased aboveground biomass, soil organic carbon, total nitrogen, available phosphorus, and microbial biomass, but decreased soil electric conductivity. Meanwhile, the relative biomasses of gram-negative bacteria decreased, while the ectomycorrhizal fungi and arbuscular mycorrhizal fungi increased after EM addition. The relationship between microbial communities and environmental factors has been changed. The restore effect of EM increased with the increase of addition time. These results indicated that EM addition could be a good practice to restore the health of the degraded alpine grassland ecosystem.

Land abandonment transforms soil microbiome stability and functional profiles in apple orchards of the Chinese Losses Plateau

Land abandonment is considered an effective strategy for ecological restoration on a global scale. However, few studies have focused on how environmental heterogeneity associated with the age of land abandonment affects the assembly and potential functions of the soil microbial community. In the present study, we investigated the community assembly of soil bacteria and fungi as well as the stability of soil networks and their potential functions in the chronosequence of abandoned apple orchards. We elucidated that the Shannon diversity of bacteria and the richness of fungi increased as land abandonment progressed. In addition, land abandonment destabilized the microbial network stability but increased network complexity. Soil available nitrogen, total carbon, and moisture are the potentially important factors in shaping the soil microbial assembly. Importantly, we showed that the microbial community diversity and functional diversity presented a synchronization effect in response to the different stages of land abandonment. Furthermore, specific bacterial taxa related to carbon fixation, dissimilatory nitrate reduction, and organic phosphorus mineralization were significantly enriched during the early abandonment stage. Collectively, these results indicate that land abandonment significantly transformed soil microbiome assembly and functional adaptation during the restoration process. These findings provide valuable insights into the influence of ecological restoration on soil microbiome and ecosystem functions in arable areas.

Macrofungi promote SOC decomposition and weaken sequestration by modulating soil microbial function in temperate steppe

Soil organic carbon (SOC) sequestration is a key grassland ecosystem function, and the magnitude of SOC reservoirs depends on microbial involvement, especially that of fungi. Mycelia developed by macrofungi potentially influence carbon (C) fixation and decomposition; however, the mechanisms underlying their effects on SOC storage in grassland ecosystems remain poorly understood. The fairy rings formed by macrofungi in grasslands are natural platform for exploring macrofungal effects on SOC. In this study, we collected topsoil (0-10 cm) from four different fairy ring zones in a temperate steppe to reveal the macrofungal effects on SOC fractions, including particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), and the SOC storage microbial mechanism using metagenomic sequencing technology. Both POC and MAOC decreased after macrofungal passage, resulting in a 7.37 % reduction in SOC. Macrofungal presence reduced microbial biomass carbon (MBC), but significantly enhanced the β-1,4-glucosidase (BG) activity, which increased dissolved organic carbon (DOC). In addition, the abundance of copiotrophs (Proteobacteria and Bacteroidetes) with lower C metabolic rates increased, and that of oligotrophs (Actinobacteria, Acidobacteria, Chloroflexi, and Verrucomicrobia) with higher substrate utilization efficiency decreased in the presence of macrofungi. This may further promote SOC decomposition. Correspondingly, there was a lower abundance of C-fixation genes but more C-degradation genes (especially hemicellulosic degradation genes) during macrofungal passage. Our results indicate that the presence of macrofungi can modulate the soil microbial community and functional genes to reduce SOC storage by inhibiting microbial C sequestration while promoting C decomposition in grassland ecosystems. These findings refine our mechanistic understanding of SOC persistence through the interactions between macrofungi and other microbes.

Effects of grazing and nitrogen application on greenhouse gas emissions in alpine meadow

Overgrazing and injudicious nitrogen applications have increased emissions of greenhouse gases from grassland ecosystems. To explore the effects and potential mechanisms of grazing, nitrogen application, and their interaction with greenhouse gas (GHG) emissions, field experiments were conducted on the Qinghai-Tibet Plateau for three consecutive years. Alpine meadow plots were subjected to light (8 sheep ha^-1) and heavy (16 sheep ha^-1) stocking rates, with or without ammonium nitrate (NH₄NO₃) (90 kg N ha^-1 yr^-1) treatment to simulate soil nitrogen deposition. During early warm growth season (May-June), peak growth season (July-September), and early cold season (October-November), static-chamber gas chromatography was used to analyze the soil's greenhouse gas emissions (CO₂, N₂O, and CH₄). Results indicated that light stocking rate (LG) led to an increase in cumulative CO₂ and N₂O emissions, while also promoting CH₄ uptake. Conversely, heavy stocking rate (HG) produced contrasting outcomes. Additionally, nitrogen applications significantly increased the short-term CO₂ and N₂O fluxes peaks. Combined treatment of nitrogen application and light stocking rate (LG + N) resulted in increased CO₂ and N₂O emissions while decreased CH₄ uptake, consequently leading to a significant increase in global warming potential. According to the structural equation model, we discovered that nitrogen application and grazing affected GHG fluxes both directly and indirectly through their impact on the environmental factors. Our findings suggest that in the context of increasing nitrogen deposition in the Qinghai-Tibet Plateau, a moderate increase in stocking rate is more effective than reducing grazing intensity for mitigating global warming potential in alpine meadow.

Progress of Ecological Restoration Research Based on Bibliometric Analysis

With the deterioration of the global/regional ecological environment, ecological restoration plays an important role in sustainable development. However, due to the differences in research methods, objectives, and perspectives, the research results are highly diverse. This makes it necessary to sort the publications related to ecological restoration, clarify the research status, grasp the research hotspots, and predict the future research trends. Here, 23,755 articles from the core database of Web of Science were retrieved, and bibliometric analysis was carried out to understand the global ecological restoration research progress from 1990 to 2022 from a macro perspective, with the aim to determine the future development direction. The results are as follows. (1) From 1990 to 2022, the number of publications in the field of ecological restoration constantly increased, and the fluctuation of the average annual citations increased. The most important articles were published in high-ranking journals. (2) Ecological restoration covers a wide range of research areas, including biodiversity, ecosystem services, climate change, land use, and ecological restoration theories and technologies. The four main hotspots in this field are heavy metal removal, soil microbial biomass carbon and nitrogen concentrations, grassland ecological restoration, and evaluation framework and modeling of ecological restoration's effects. Currently, studies focus on river basin remediation, heavy metal removal, and forest restoration. (3) Future ecological restoration research should strengthen the multi-object aspect and multi-scale ecological restoration research, improve the ecological restoration effect evaluation system, and incorporate social and economic issues. This study identified current research hotspots and predicted potential future research directions, providing a scientific reference for future studies in the field of ecological restoration.