Soil Ecosystem Functioning Research Articles

Red imported fire ant nesting affects the structure of soil microbial community.

The red imported fire ants (RIFA, Solenopsis invicta) have become a well-known invasive species that poses significant ecological and economic threats globally. As of recent times, the geographic scope of its invasion in China is rapidly expanding, thereby aggravating the extent and severity of its detrimental effects. The importance of soil microorganisms for maintaining soil health and ecosystem function has been widely acknowledged. However, the negative impact of RIFAs on soil microbial communities and their functions has not yet been fully understood. In this study, we sequenced the V3-V4 variable region of the bacterial 16S rRNA gene in soil samples collected from three types of RIFA nests to investigate the impact of RIFA invasion on soil microbial diversity and composition. The results of alpha diversity analysis showed that the normal soil without nests of RIFAs exhibited the highest level of diversity, followed by the soil samples from RIFA-invaded nests and abandoned nests. Taxonomy and biological function annotation analyses revealed significant differences in microbial community structure and function among the different samples. Our findings demonstrate that RIFA invasion can significantly alter soil microbial community composition, which could ultimately affect ecosystem function. Therefore, effective management strategies are urgently needed to mitigate the negative impact of invasive species on native ecosystems.

Composition of soil organic matter and the structure and diversity of soil bacteria and archaea, in crop systems under no-till in a subtropical ecosystem

Crop richness in crop rotation systems may modulate soil microbial activity and the diversity of community structure, driving soil organic matter (SOM) content and quality. We aimed to assess the long-term effect of crop systems on SOM composition and the structure and diversity of the bacteria and archaea in no-till subtropical soil. The study was based on samples from a subtropical Ferralsol subjected to 27 years of crop succession (wheat/soybean) or crop rotation (vetch/maize/wheat/soybean). Soil samples were analyzed in relation to C and N contents, and submitted to DNA extraction for 16 S rDNA sequencing and 13C Nuclear Magnetic Resonance spectroscopy – solid-state (CP/MAS 13C NMR). The effect of the current crop species at the time of sampling on the structure and diversity of the microbial community was predominant in relation to the long-term crop history over time (crop rotation). A greater diversity and abundance of soil bacteria and archaea was observed in the area with wheat growing in winter than with soybean growing in summer, a combined effect of crop species and season. The soil under crop rotation had a greater proportion of carbohydrate-derived C in SOM, whereas a greater proportion of alkyl-C and N/O alkyl-C was observed under crop succession. The crop species richness in crop rotation allows the maintenance of soil functions related to the formation of more biochemically labile SOM and contributes positively to soil ecosystem functioning.

Evaluating the role of bacterial diversity in supporting soil ecosystem functions under anthropogenic stress

Ecosystem functions and services are under threat from anthropogenic global change at a planetary scale. Microorganisms are the dominant drivers of nearly all ecosystem functions and therefore ecosystem-scale responses are dependent on responses of resident microbial communities. However, the specific characteristics of microbial communities that contribute to ecosystem stability under anthropogenic stress are unknown. We evaluated bacterial drivers of ecosystem stability by generating wide experimental gradients of bacterial diversity in soils, applying stress to the soils, and measuring responses of several microbial-mediated ecosystem processes, including C and N cycling rates and soil enzyme activities. Some processes (e.g., C mineralization) exhibited positive correlations with bacterial diversity and losses of diversity resulted in reduced stability of nearly all processes. However, comprehensive evaluation of all potential bacterial drivers of the processes revealed that bacterial α diversity per se was never among the most important predictors of ecosystem functions. Instead, key predictors included total microbial biomass, 16S gene abundance, bacterial ASV membership, and abundances of specific prokaryotic taxa and functional groups (e.g., nitrifying taxa). These results suggest that bacterial α diversity may be a useful indicator of soil ecosystem function and stability, but that other characteristics of bacterial communities are stronger statistical predictors of ecosystem function and better reflect the biological mechanisms by which microbial communities influence ecosystems. Overall, our results provide insight into the role of microorganisms in supporting ecosystem function and stability by identifying specific characteristics of bacterial communities that are critical for understanding and predicting ecosystem responses to global change.

Contrasting responses of nematode composition, richness and biomass to long-term warming

It is well established that climate warming has become a growing issue globally, posing a threat to native ecosystems. Alpine ecosystems, such as meadows of the Qinghai-Tibet Plateau, are expected to be particularly sensitive to warming given current temperature constraints. While many studies have explored the effects of warming on aboveground ecosystems and edaphic properties, few studies have assessed the effects on soil biota. We assessed edaphic, plant, microbial and nematode responses to warming in a long-term (8 year) multilevel warming experiment and applied piecewise structural equation modelling to reveal how warming affected nematode communities directly and indirectly via biotic and abiotic factors. We found that (1) warming had a significant effect on nematode community composition, which was mainly due to direct warming effects on herbivores and omnivore-predatory nematode composition; (2) warming affected nematode richness mainly through effects on bacterial richness, with a strong negative relationship between bacterial richness and bacterivore richness as well as bacterivore richness and omnivore-predatory richness; and, (3) the predominantly direct effect of warming on nematode biomass was mainly due to significant responses of omnivore-predatory biomass. Our study provides insight into the effects of long-term warming on nematode communities and highlights the contrasting responses of composition, diversity and biomass to warming. It contributes to forecasting warming effects on the structure of soil food webs and ecosystem functioning on the Qinghai-Tibet plateau in the future.

Historical and future variation of soil organic carbon in China

Revealing historical changes in soil organic carbon (SOC) and exploring its future status are important for safeguarding soil health and food security, giving full play to the service function of soil ecosystems, and coping with climate change. However, there is still a gap in our understanding of the SOC stocks in China and their spatial patterns in response to future climate change. Therefore, we attempted to fill this knowledge gap using a large amount of soil observation data, digital soil mapping technology, and global circulation models from Coupled Model Inter-comparison Project phase 6 (CMIP6). In this study, a random forest model was selected to construct the spatial relationship between SOC in the top 0–20 cm (SOC020) and 0–100 cm (SOC0100) of the soil and 21 environmental factors. Spatiotemporal changes in SOC from 1980 to 2100 were revealed at a resolution of 1 km and five-year interval for three climate scenarios in CMIP6. The cross-validation results indicated acceptable predictions for both depths of SOC; however, relatively large prediction uncertainties were observed for SOC0100 in the Tibetan Plateau and northeastern China. The mean values of SOC020 and SOC0100 over the last four decades were 35.77 and 84.62 Tg, respectively, and showed carbon sinks at the national scale, with accumulation rates of 0.05 Pg yr-1 and 0.036 Pg y-1 for the two depths. Compared with historical values (1980–2020), SOC will fluctuate significantly in the future under different climate scenarios. Among them, SOC showed a slow increasing trend at both depths under the SSP1-1.9 low emission scenario, while SOC presented a decreasing trend under the SSP2-4.5 and SSP5-8.5 medium–high emission scenarios. In particular, in most of China under the SSP2-4.5 scenario, SOC0100 presented a larger likelihood of being a carbon source. This study provides a reference for exploring the response of soil carbon pools to climate change and evaluating the effectiveness of land management and ecological protection.

Distribution Pattern of Bacterial Community in Soil Profile of Larix principis-rupprechtii Forest in Luya Mountain

Microbial communities are the key component to maintaining the structure and function of forest soil ecosystems. The vertical distribution of bacterial communities on the soil profile has an important impact on forest soil carbon pools and soil nutrient cycling. Using Illumina MiSeq high-throughput sequencing technology, we analyzed the characteristics of bacterial communities in the humus layer and 0-80 cm soil layer of Larix principis-rupprechtii in Luya Mountain, China, to explore the driving mechanisms affecting the structure of bacterial communities in soil profiles. The results showed that the α diversity of bacterial communities decreased significantly with increasing soil depth, and community structure differed significantly across soil profiles. The relative abundance of Actinobacteria and Proteobacteria decreased with increased soil depth, whereas the relative abundance of Acidobacteria and Chloroflexi increased with the increase in soil depth. The results of RDA analysis showed that soil NH+4, TC, TS, WCS, pH, NO-3, and TP were important factors determining the bacterial community structure of the soil profile, among which soil pH had the most significant effect. Molecular ecological network analysis showed that the complexity of bacterial communities in the litter layer and subsurface soil (10-20 cm) was relatively high, whereas the complexity of bacterial communities in deep soil (40-80 cm) was relatively low. Proteobacteria, Acidobacteria, Chloroflexi, and Actinobacteria played important roles in the structure and stability of soil bacterial communities in Larch. The species function prediction of Tax4Fun showed a gradual decline in microbial metabolic capacity along the soil profile. In conclusion, soil bacterial community structure showed a certain distribution pattern along the vertical profile of soil, the community complexity gradually decreased, and the unique bacterial groups of deep soil and surface soil were significantly different.

Post-Harvest Eucalyptus Residue Removal Reduces Soil Aggregation and Biological Activities in Central-West Brazil

Tree residue removal from Eucalyptus plantations after timber harvest can reduce soil functioning by reducing the organic matter input. To assess the effects of residue management systems (RMS) on soil aggregation, carbon (C) and nitrogen (N) content, and biological activities, a field trial was conducted in a commercial Eucalyptus plantation (loamy sand soil) in Mato Grosso do Sul, Brazil. The study assessed three RMS: cut-to-length (CTL), tree-length (TL), and bare litter (BL), respectively. After 21 months, undisturbed soil samples were collected and physically isolated into three aggregate-size fractions: large macroaggregates (LM), medium macroaggregates (SM), and microaggregates (MI). Results showed that these soils are mostly composed of LM (54%), and that removing harvest residues from the growing site included total organic carbon (TOC) by 28%, microbial biomass-C by 20%, fluorescein diacetate hydrolysis by 17%, and β-glucosidase activity by 26%, when compared to CTL. TL outperformed CTL for the proportion of LM and LM-associated TOC. Across fractions, a higher microbial quotient was observed in SM and MI fractions, suggesting that the TOC has higher stability inside the LM. This study suggests that leaving harvest residues on the soil should be recommended for Eucalyptus plantations, especially in low-fertility sandy soils, as it helps in maintaining the soil structure and biological activities critical for soil health and ecosystem function.

Rhizosphere effect on the relationship between dissolved organic matter and functional genes in contaminated soil

Arsenic contamination in a mining area is a potential threat to the local population. In the context of one-health, biological pollution in contaminated soil should be known and understandable. This study was conducted to clarify the effects of amendments on arsenic species and potential threat factors (e.g., arsenic-related genes (AMGs), antibiotic resistance genes (ARGs) and heavy-metal resistance genes (MRGs)). Ten groups (control (CK), T1, T2, T3, T4, T5, T6, T7, T8, and T9) were set up by adding different ratio of organic fertilizer, biochar, hydroxyapatite and plant ash. The maize crop was grown in each treatment. Compared with CK, the bioavailability of arsenic was reduced by 16.2%–71.8% in the rhizosphere soil treatments, and 22.4%–69.2% in the bulk soil treatments, except for T8. The component 2 (C2), component 3 (C3) and component 5 (C5) of dissolved organic matter (DOM) increased by 22.6%–72.6%, 16.8%–38.1%, 18.4%–37.1%, respectively, relative to CK in rhizosphere soil. A total of 17 AMGs, 713 AGRs and 492 MRGs were detected in remediated soil. The humidification of DOM might directly correlate with MRGs in both soils, while it was influenced directly on ARGs in bulk soil. This may be caused by the rhizosphere effect, which affects the interaction between microbial functional genes and DOM. These findings provide a theoretical basis for regulating soil ecosystem function from the perspective of arsenic contaminated soil.

Impact of anthropogenic activities on soil microorganisms: A review

In the world, since the beginning of mankind soil has been the basis for the sustenance of life. The discovery of microorganisms within soil and their importance in recycling organic matter dates back to the 17th century when John Evelyn stated that soil fertility could be maintained by the addition of organic materials. By the 20th century, large farming devices and chemicals for improving the production of crops on a large scale had been developed and the utilization of these resources resulted in drastic increases in land areas under cultivation. Although agricultural chemicals and machinery increased crop productivity exponentially, the intensive application of these agricultural management tools has also had many negative effects on agricultural soils. As a result the impacts of human activities on soil microorganisms are many and varied. The effects of human activities vary with land use, ranging from agricultural wastes such as farm animal sewerage and fertilizer runoff, to commercial and industrial wastes of every conceivable type and magnitude. A better understanding of the linkages between soil life and ecosystem function and the impact of human interventions will enable the reduction of negative impacts and the more effective capture of the benefits of soil biological activity for sustainable and productive agriculture. Therefore the objective of this review was to summarize the literatures and the current knowledge on the impact of different anthropogenic activities on soil microorganisms.

Omics Approaches in Invasion Biology: Understanding Mechanisms and Impacts on Ecological Health.

Invasive species and rapid climate change are affecting the control of new plant diseases and epidemics. To effectively manage these diseases under changing environmental conditions, a better understanding of pathophysiology with holistic approach is needed. Multiomics approaches can help us to understand the relationship between plants and microbes and construct predictive models for how they respond to environmental stresses. The application of omics methods enables the simultaneous analysis of plant hosts, soil, and microbiota, providing insights into their intricate relationships and the mechanisms underlying plant-microbe interactions. This can help in the development of novel strategies for enhancing plant health and improving soil ecosystem functions. The review proposes the use of omics methods to study the relationship between plant hosts, soil, and microbiota, with the aim of developing a new technique to regulate soil health. This approach can provide a comprehensive understanding of the mechanisms underlying plant-microbe interactions and contribute to the development of effective strategies for managing plant diseases and improving soil ecosystem functions. In conclusion, omics technologies offer an innovative and holistic approach to understanding plant-microbe interactions and their response to changing environmental conditions.

The Impact of Tree Species on Microbial Community Structure and Soil Function on Forest Plantations in the Central Hardwoods Region (CHR)

Interactions between above- and below-ground monoculture forest plantation components are critical to tree growth and development. Within the Central Hardwoods Region (CHR), synergistic relationships between tree species and soil microbial community structure and function have received limited research attention. Soil microbes are integral to forest ecosystems as their activities intrinsically promote soil organic matter decomposition, nutrient cycling, and ecosystem functioning. Here, we examined soils from two perfectly aligned stands of black walnut (BW, Juglans nigra L.) and Northern red oak (RO, Quercus rubra L.) trees. Measurements of selected soil chemical properties, microbial community structure using ester-linked fatty acid methyl ester (EL-FAME), and soil enzyme activities (EAs) were used. Analysis of modifications within microbial communities showed a significant positive response to BW based upon soil EAs and microbial indicators, compared to RO. Seasonal comparisons predictably revealed higher microbial activities during summer. Fungi dominated the soil microbial community structure with a fungal/bacterial ratio of 2:1. Gram-positive rather than Gram-negative bacteria or actinomycetes dominated the bacterial community. The activity of the soil enzymes ß-glucosidase and arylsulfatase increased, but ß-glucosaminidase and acid phosphatase decreased. Additionally, acid phosphatase and arbuscular mycorrhizal fungi revealed strong correlations. The differences observed in biological properties, specifically microbial communities and EAs, highlight the varied responses to BW and RO soil biology and subsequent soil ecosystem functions. These results indicate that variations in microbial abundance and soil functions occur throughout the course of an entire year.

Changes in fungal diversity and key-stone taxa along soil-eroding catena

Fungal communities play an important role in soil biogeochemical cycles and ecosystem function. The redistribution of water and soil causes significant differences in the soil physicochemical properties in eroding landscapes. However, changes in soil fungal diversity and key-stone taxa in soil-eroding catena remain poorly understood in these landscapes. In the current study, the diversity and key-stone taxa of the fungal community in topsoil samples were analyzed from three typical erosive topographic units (autonomous, transitional, and depositional zones). The Chao 1 index showed a decrease from the autonomous and transitional zones (1759.7 and 1752.6, respectively) to the depositional zone (1535.3), but there were no significant differences in the Shannon index. Transitional and depositional networks had fewer edges (318 and 387, respectively) and clustering coefficients (0.236 and 0.301, respectively) than the autonomous network (911 and 0.362, respectively). At the phylum level, the nutritional strategists of key-stone taxa tended to shift from r- to K-strategists along the soil-eroding catena, indicating that the majority of key-stone taxa were dominated by the phylum Ascomycota in the autonomous and transitional zones, whereas the phylum Basidiomycota was dominant in the depositional zone. The recalcitrant carbon composition (CC/CO, autonomous vs. transitional vs. depositional: 3.82 vs. 5.09 vs. 7.52) may have contributed to the decreased fungal richness along the soil-eroding catena. The primary controlling factors affecting key-stone taxa were soil organic carbon (SOC), total nitrogen (TN) and Olsen-P in the autonomous zone, SOC and CH/CO in the transitional zone, and CC/CO in the depositional zone. Exploring the changes in fungal diversity and key-stone taxa among different erosive topographic units can contribute to an in-depth understanding of the biogeochemical cycle in the eroding environment.

Soil Macrofauna Disperse and Reconstruct Soil Nematode Communities: Takeaways from a Microcosm Study

Soil macrofauna is an important component of soil biodiversity and plays a key role in soil ecosystem function. Little work, however, has explored how macrofauna may contribute, directly or indirectly, to soil microfauna communities. In this study, we explored the impact of two classes of common soil macrofauna, earthworms (Eisenia foetida) and millipedes (Spirobolus walkeri), on soil nematode community diversity and structure. We found that earthworms and millipedes play an important role in maintaining soil nematode communities and increasing soil nutrients. Both earthworms and millipedes act as hosts for soil nematodes, and play a valuable role in dispersing and distributing these important microfauna throughout the soil landscape. We tested the efficacy of this strategy on multiple soil layers and found that layer does not have a significant influence on soil nematode community. These results suggest that soil nematode abundance, diversity, and structure are tightly linked to the existence of soil macrofauna, which may contribute to the maintenance mechanism of forest soil biodiversity.

Land use modification causes slow, but predictable, change in soil microbial community composition and functional potential

BackgroundBacterial communities are critical to ecosystem functioning and sensitive to their surrounding physiochemical environment. However, the impact of land use change on microbial communities remains understudied. We used 16S rRNA gene amplicon sequencing and shotgun metagenomics to assess soil microbial communities' taxonomic and functional responses to land use change. We compared data from long-term grassland, exotic forest and horticulture reference sites to data from sites that transitioned from (i) Grassland to exotic forest or horticulture and from (ii) Exotic forest to grassland.ResultsCommunity taxonomic and functional profiles of the transitional sites significantly differed from those within reference sites representing both their historic and current land uses (P < 0.001). The bacterial communities in sites that transitioned more recently were compositionally more similar to those representing their historic land uses. In contrast, the composition of communities from sites exposed to older conversion events had shifted towards the compositions at reference sites representing their current land use.ConclusionsOur study indicates that microbial communities respond in a somewhat predictable way after a land use conversion event by shifting from communities reflecting their former land use towards those reflecting their current land use. Our findings help us to better understand the legacy effects of land use change on soil microbial communities and implications for their role in soil health and ecosystem functioning. Understanding the responsiveness of microbial communities to environmental disturbances will aid us in incorporating biotic variables into soil health monitoring techniques in the future.

Impacts of shrubs on soil quality in the native Monte rangelands of Southwestern Buenos Aires, Argentina

AbstractShrub cover in semiarid rangelands may induce changes in soil resources and ecosystem functioning. However, it is unknown the real influence that shrub vegetation has on soil quality in rangelands used for livestock purposes. We evaluated the shrub cover effect on 12 chemical and biochemical parameters of soil quality. In a semiarid Monte rangeland of Argentina, 6 paddocks were selected and 10 m transects were placed in a patch with (Sh) and without shrubs (WSh). Then, sites with grasses (Sh‐G and WSh‐G), bare ground‐litter (Sh‐BL and WSh‐BL), and under shrub cover (Sh‐S) were selected. In spring 2017 and 2018, a composite soil sample (0–10 cm in depth) was taken at each site (n = 6). Sh‐G and Sh‐S sites presented high values of soil organic matter, soil organic nitrogen, particulate organic matter (POM), and cellulase activity (CA); WSh‐BL and Sh‐BL sites were associated with the lowest contents of these variables. For the rest of the soil quality parameters, the soil sampling sites showed similar values. These results show that woody presence should not be directly linked to soil quality loss. Although we did not detect a shrub effect in all parameters studied, in the context of appropriate grazing management, the presence of plant species of different functional groups has a positive effect on organic matter and N content of soil close to them. Moreover, in these sites, high POM values represent an important reservoir of potentially available nutrients, and promote CA necessary for fresh litter decomposition improving the soil quality of semiarid rangelands.

Analog soil organo–ferrihydrite composites as suitable amendments for cadmium and arsenic stabilization in co-contaminated soils

Remediation of CdAs co-contaminated soils has long been considered a difficult problem to solve, as Cd and As have distinctly different metallic characters. Amending contaminated soils with traditional single passivation materials may not always work well in the stabilization of both Cd and As. Here, we reported that analog soil organo–ferrihydrite composites made with either living or non-living organics (bacterial cells or humic acid) could achieve stabilization of both Cd and As in contaminated soils. BCR and Wenzel sequential extractions showed that organo–ferrihydrite, particularly at 1 wt% loading, shifted liable Cd and As to more stable phases. Organo–ferrihydrite amendments significantly (p < 0.05) increased soil urease, alkaline phosphatase and catalase enzyme activities. With organo–ferrihydrite amendments, the bioavailable fraction of Cd decreased to 35.3 % compared with the control (65.1 %), while the bioavailable As declined from 29.4 % to 12.4%. Soil pH, microbial community abundance and diversity were almost unaffected by organo–ferrihydrite. Ferrihydrite and organo fractions both contributed to direct Cd-binding, while the organo fraction probably maintained the Fe-bound As via lowering ferrihydrite phase transformation. Compared to pure ferrihydrite, organo–ferrihydrite composites performed better not only in reducing liable Cd and As, but also in maintaining soil quality and ecosystem functions. This study demonstrates the applications of organo–ferrihydrite composites in eco-friendly remediation of CdAs contaminated soils, and provides a new direction in selecting appropriate soil amendments.

Impact of intercropping grass on the soil rhizosphere microbial community and soil ecosystem function in a walnut orchard.

The intercropping of grass in orchards has beneficial effects on soil properties and soil microbial communities and is an important soil management measure for improving orchard productivity and land-use efficiency. However, few studies have explored the effects of grass intercropping on rhizosphere microorganisms in walnut orchards. In this study, we explored the microbial communities of clear tillage (CT), walnut/ryegrass (Lolium perenne L.) (Lp), and walnut/hairy vetch (Vicia villosa Roth.) (Vv) intercropping system using MiSeq sequencing and metagenomic sequencing. The results revealed that the composition and structure of the soil bacterial community changed significantly with walnut/Vv intercropping compared to CT and walnut/Lp intercropping. Moreover, the walnut/hairy vetch intercropping system had the most complex connections between bacterial taxa. In addition, we found that the soil microorganisms of walnut/Vv intercropping had a higher potential for nitrogen cycling and carbohydrate metabolism, which may be related to the functions of Burkholderia, Rhodopseudomonas, Pseudomonas, Agrobacterium, Paraburkholderia, and Flavobacterium. Overall, this study provided a theoretical basis for understanding the microbial communities associated with grass intercropping in walnut orchards, providing better guidance for the management of walnut orchards.

Stoichiometric Soil Microbial and Enzymatic Characteristics under Three Different Plantation Types in China’s Luya Mountain

It is important to maintain soil ecosystem function and ecological balance stability. This study uses ecological stoichiometry to ascertain relational constraints of soil nutrient (i.e., carbon (C), nitrogen (N), phosphorus (P), etc.) cycling mechanisms and associated ecological balance characteristics in China’s temperate Luya Mountain Nature Reserve. To clarify changes and driving factors associated with soil and extracellular enzyme stoichiometry under different plantation types in July 2021, we analyzed soil nutrient, soil extracellular enzyme, and soil microbial stoichiometry characteristics and their key influencing factors in a Picea asperata Mast. forest, a Caragana jubata (Pall.) Poir. shrubland, and a Carex lanceolata Boott meadow in this reserve. Results revealed significant differences in soil physical and chemical properties, microbial biomass, soil extracellular enzyme activity, and stoichiometry among these different plantation types. Compared to the shrubland and forest plantations, meadow plantation soil was more severely C restricted while that of all three plantations was more N restricted. The main influencing soil stoichiometric ratios were total carbon (TC), total nitrogen (TN), total phosphorus (TP), ammonium (NH4+-N), soil water content (SWC), β-glucosidase, and microbial C, N, and P biomass. Effects associated with soil N:P, enzymatic N:P, enzymatic C:P, microbial C:N, microbial N:P, and microbial C:P ratios were important for bacterial and fungal community soil structure. This study provides a scientific basis to explicate microbial and regulatory effects of soil extracellular enzyme stoichiometry under different plantation types in one of China’s best preserved and most concentrated natural secondary forests.

Natural restoration enhances soil multitrophic network complexity and ecosystem functions in the Loess Plateau

Natural restoration of abandoned land is a widely used strategy to restore ecosystem functions. Previous studies mainly focused on restoring the diversity of a limited number of organism groups, ignoring that biodiversity loss occurs across multiple trophic levels and that ecological processes depend on complex interactions. In this study, the effects of natural restoration on diversity and network of multiple soil trophic groups and 10 variables related to a broad range of ecosystem functions were investigated along a 50-year natural restoration chronosequence. The diversity of different trophic groups had distinct responses to natural restoration. Furthermore, the complexity of soil networks, indicated by co-occurrence patterns across trophic levels, significantly increased with progressing succession. Ecosystem multifunctionality was significantly positively associated with soil network complexity than diversity in all individual and multiple trophic groups (multitrophic diversity). After controlling for confounding factors of ecosystem multifunctionality, these relationships remained robust, including geographic location and soil attributes. Moreover, the positive association between multifunctionality and soil biodiversity across restoration sites could be indirectly due to the soil network complexity. Diversity levels of soil archaea and invertebrates, and soil nutrient cations were significantly associated with the interconnectivity of complex multitrophic networks. Therefore, this study provides insights into the important role of soil network structure in maintaining ecosystem functioning, highlighting the necessity of considering potential interactions among soil organisms in the restoration of degraded ecosystems rather than simply focusing on the number of species.

Nitrogen enrichment amplifies the effects of litter treatments on soil microorganisms and ecosystem functions in grazed and non-grazed grasslands

Litter removal or addition and nitrogen (N) enrichment are two important methods for restoring grasslands. Despite the litter alteration and N enrichment effect on soil microorganisms in different ecological systems of independent have got the good evaluation, it is still unknown how N enrichment modifies the effects of litter removal and addition on soil microorganisms and ecosystem function in different grasslands. Here, we conducted two independent experiments to assess the effects of litter addition/removal and N enrichment on soil microorganisms and ecosystem functions in a typical grassland. In a litter-removal experiment, we evaluated how N addition regulated the effect of litter removal in a long-term non-grazed grassland. In a litter-addition experiment, we evaluated how N addition regulated the effect of litter addition in a long-term over-grazed grassland. We found that the response of plant communities to removal/addition of litter and N enrichment was relatively minor in both non-grazed and grazed grasslands; the high precipitation during the sampling year may mask the effects of the litter and N treatments on plant community. Litter addition in the grazed grassland increased fungal and AMF biomass and decreased bacteria: fungi ratio, but litter removal in the non-grazed grassland had only minor effects on soil microbial variables. Litter removal in the non-grazed grassland and litter addition in the grazed grassland had different effects on soil carbon (Cmin) and N mineralization (Nmin), but N enrichment consistently reduced soil Cmin and Nmin in non-grazed and grazed grasslands. In addition, N enrichment amplified the effects of litter treatments on soil microorganisms and mineralization. These findings indicate that removal of litter from non-grazed grasslands and addition of this litter to grazed grasslands may help to restore grasslands, and the amount of N enrichment should be adjusted to optimize the positive effect of nitrogen enrichment and weaken the negative effect of nitrogen enrichment. Overall, our experimental results revealed that the effects of litter treatment on soil microorganisms and mineralization in grazed and non-grazed semi-arid grasslands are amplified by N enrichment.