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Soil organic carbon (SOC) fractions are influenced by inputs of nitrogen (N) from globally rising N deposition; however, the mechanisms of how soil microbiological properties are influenced by N deposition and its impact on the fractional distribution and stability of SOC remain unclear. In this study, we assessed the effects on SOC fraction distribution and stability from four aspects of soil microbiological properties: soil microbial biomass (SMB), soil microbial activity, structure diversity, and functional diversity of soil microbial community in a Pinus tabuliformis plantation, which received four N addition levels (0 g N m−2 y−1 (N0), 3 g N m−2 y−1 (N3, low N addition), 6 g N m−2 y−1 (N6, mid-N addition), and 9 g N m−2 y−1 (N9, high N addition)) for 2 years. The N inputs did significantly affect some soil microbiological properties, like SMB, soil phospholipid fatty acid (PLFA), and soil microbial functional diversity. Mid- and high N addition decreased the richness (HPLFA) and evenness (EPLFA) index of the soil microbial community, from 3.24 to 2.91 and 0.93 to 0.87, respectively. In addition, the low N addition promoted the carbon management index (CMI) to 141.35, i.e., higher than the CMIs in the mid- and high-level treatments. The SOC stability also showed significant differences among N addition treatments, and SOC could be the most stable at the mid-N addition level. Regarding the effects of the four soil microbiological attributes on the CMI and stability, SMB and soil respiration positively impacted the CMI, but did not significantly affect the stability. In addition, EPLFA had positive effects, but EBIOLOG had negative effects on CMI and lability. Our findings indicate that soil microbiological properties are essential in SOC fractional distributions and stability. Further identification and study of soil microbial species used to change SOC fractions would help to clarify the detailed mechanisms involved. [ABSTRACT FROM AUTHOR]

Purpose: A general understanding of the influence of different plant species on soil quality improvement under drought stress is vital for planning the restoration of degraded land resources, especially in the context of global warming. Methods: In this pot study, we planted Setaria viridis, Stipa bungeana, and Bothriochloa ischaemum, which are typical grass species on abandoned farmland, succeeded by grassland, in the Loess Plateau of China, under optimal soil water conditions and under water deficit (i.e., 80% and 60% of soil field capacity, respectively). Rhizosphere soil samples of the three grass species were collected after 76 days of growth, and 21 soil properties were determined as potential indicators of soil quality. Four rhizosphere soil quality indices (SQI) were computed using linear/nonlinear scoring functions and additive/weighted additive methods by the selected minimum dataset (MDS). Results: L-leucine aminopeptidase, cellobiohydrolase, phenol oxidase, total phosphorus, available phosphorus, nitrate nitrogen, water-soluble nitrate nitrogen, and water-soluble ammonium nitrogen constituted the MDS for SQI calculation. The nonlinear weighted additive index best discriminated the effects of grass species under drought stress. Rhizosphere SQI did not significantly differ among the three grass species under optimal water conditions, but drought stress exerted a positive effect on rhizosphere SQI, which was significant for S. viridis. Conclusion: Short-term drought stress increased rhizosphere SQI, especially at the preliminary succession stages. Furthermore, the relatively stable rhizosphere SQI of plant species at the later-successional stages suggests that the later-successional plant species resisted drought stress better; this aspect warrants further investigation. [ABSTRACT FROM AUTHOR]

Microbes play an essential role in soil biogeochemical processes and maintenance of soil nutrients, but not all microbial taxa contribute equally, and their functions in soil nutrient cycling and microbial network stability are unclear in arid fertigation agricultural ecosystems.In this study, a 4‐year field experiment was conducted in an irrigation district in China using three levels of irrigation [high (400 mm), medium (300 mm) and low (200 mm)] and two levels of fertilization [high (600 kg/ha P2O5 + 300 kg/ha urea) and low (300 kg/ha P2O5 + 150 kg/ha urea)] to reveal the ecological roles of core and noncore taxa in maintaining soil nutrient cycling and their associations with microbial network stability.Our results showed that combining medium irrigation with low fertilization resulted in higher levels of soil organic C, inorganic N, available P, multinutrient cycling and noncore bacterial diversity compared with the other treatments. Soils supporting a higher diversity of noncore bacterial taxa had a high soil multinutrient cycling index, while soils harbouring highly diverse core taxa exhibited a more stable bacterial network. The soil multinutrient cycling index was also significantly positively related to the subnetwork modularity of noncore taxa. Moreover, noncore taxa could serve as diverse pools that turn into core taxa in response to changes in the external environment. Acinetobacter, Flavobacterium, Gemmatimonas and Salinimicrobium, which belong to the noncore taxa, were involved in soil C and N cycling in the arid agricultural ecosystem.Synthesis and applications. Our results suggest that soil microbiota contribute differently to ecosystem functions. Changes in soil nutrient cycling were more closely related to variations in noncore taxa, while bacterial network stability was more associated with core taxa. Our study emphasized the role of noncore microbiota, which has been neglected in previous studies. Furthermore, our findings suggested that combining medium irrigation with low fertilization is effective for enhancing soil nutrients and bacterial diversity, providing guidance for managing arid agricultural ecosystems. [ABSTRACT FROM AUTHOR]

Nutrient addition can alter plant–soil‐microbe interactions. However, knowledge remains limited about how the soil biotic and abiotic properties drive changes in plant community composition and diversity after nitrogen (N) addition. In this study, four N addition rates (N0, N3, N6, and N9: 0, 3, 6, and 9 g N m −2 yr−1) were applied to a grassland community on the Loess Plateau (China) to evaluate the response of plant community biomass, evenness, and composition to N addition. Overall, N addition significantly increased plant shoot and root biomass by 27.75%–31.37% and 39.60%–65.42% compared with N0, but no significant difference was observed among N3, N6, and N9. N addition significantly decreased shoot/root biomass ratio by 7.17%–21.84%, and plant community evenness by 3.80%–8.80% compared with N0, particularly under N3 and N6 treatments. Furthermore, N addition enhanced the abundance of bacteria and fungi, but their composition was not altered. Responses of plant biomass and evenness to N addition were correlated to changes in NO3−‐N, soil total phosphorus, and the abundance of bacteria and fungi; additionally, the composition was primarily affected by the microbial abundance. Our research indicates that N addition can significantly alter plant community composition, particularly at low addition rates, and such alteration may be more affected by the soil microbial abundance. The findings of this study have important implications for the sustainable management of grassland ecosystems. [ABSTRACT FROM AUTHOR]

Aims: Extensive studies have demonstrated a significant impact of nitrogen (N) addition on microbial community diversity, composition, and functions in various soils. However, microbial co-occurrence patterns and assembly processes under enhanced N levels is less known, especially with respect to the rhizosphere where microbes are closely linked with plant growth. Methods: In this study, we performed a pot experiment using N addition gradient (0, 2.5, 5, 7.5, 10, and 15 g N·m−2·year−1) and amplicon sequencing and metabolomics to investigate the effect of short-term N addition (2 years) on the co-occurrence patterns and assembly process of bacterial communities as well as their potential drivers in the rhizosphere. Results: Short-term N addition significantly altered bacterial community diversity and composition in the rhizosphere soil but not in the bulk soil; i.e., the rhizosphere bacterial diversity increased with N addition but decreased under high N input (>5 g N·m−2·year−1). The rhizosphere co-occurrence networks showed a more complex topology than the bulk soil, and this complexity could be strengthened by the quantity of N added. The N-induced establishment of the bacterial community in the rhizosphere was mainly dominated by deterministic processes with an increase in the variable selection in response to the increase in the N-addition rate, while the bacterial community in the bulk soil exhibited a transition from stochastic to deterministic processes. N addition stimulated the release of amino acids and short-chain organic acids into the rhizosphere, and these changes in root exudates and the soil NH4+-N level were mainly responsible for the changes in the structure of the rhizosphere bacterial community and co-occurrence networks of keystone species. Conclusions: Our results demonstrated the differences in the co-occurrence patterns and assembly processes of bacterial communities between rhizosphere and bulk soils under N addition, which were closely associated with root exudates. These findings improve our understanding of plant–microbial interactions. [ABSTRACT FROM AUTHOR]

Purpose: Knowledge of soil N cycling and the associated functional microbial groups of N2O production under different management measures could provide clues for the restoration of degraded meadows in alpine ecosystems. Materials and methods: We investigated soil N2O emissions, the genes related to N2O production and reduction (AOA-amoA, AOB-amoA, nirK, nirS, and nosZ), and associated microbial communities in four meadows (continuous grazing, grazing exclusion by fencing, grazing exclusion by combined fencing and reseeding, and undisturbed meadow) in the Tibetan Plateau to reveal the mechanism underlying potential N2O emissions in alpine meadows. Results and discussion: Compared to the grazing meadow, fencing and fencing + reseeding meadows had lower N2O emissions and lower abundances of AOA-amoA, AOB-amoA, nirK, nirS, and nosZ genes, suggesting that grazing exclusion could decrease the soil N-turnover potential. However, the higher N2O emissions compared to those of undisturbed meadows indicated that longer restoration periods were necessary. Seeding the fenced meadow did not alter soil N2O emission or the abundance of AOA-amoA, AOB-amoA, nirK, nirS, and nosZ genes, possibly owing to the similar soil nutrient status compared to that of the fencing meadow. Grazing exclusion also resulted in significant changes in the community diversity and composition of microbes harboring these functional genes, especially nirK and nosZ communities. N2O emissions were significantly associated with microbial communities involved in N2O production and reduction but not with the gene abundance of AOA-amoA, AOB-amoA, nirK, nirS, and nosZ. Soil dissolved organic nutrients, including C and N, and soil moisture were the controlling factors for N2O production by altering the community composition of nirK- and nosZ-type denitrifiers, such as Bradyrhizobiaceae, Rhizobiaceae, Brucellaceae, Ochrobactrum, and Proteobacteria. Conclusions: Our results indicated that grazing-induced elevation of potential N2O emissions from meadow soil could be alleviated by grazing exclusion, including sole fencing and a combination of fencing and reseeding, by changing soil dissolved organic nutrients and moisture thus regulating the microbial communities. [ABSTRACT FROM AUTHOR]

Aims: High plant diversity is usually linked with high soil microbial diversity, which is hypothesized to be attributed to a high diversity of components in the soil leachate, but experimental evidence is scarce. The aim of this study was to determine if the variation in soil leachate caused by plant diversity could affect the soil microbial community. Methods: A microcosm experiment was conducted to determine the effect of plant diversity on the soil microbial community by measuring soil leachate in a gradient of plant richness from levels 1 (one species) to 3 (three species). Results: Plant richness significantly affected the diversity of soil leachate and microbial communities. The amount and diversity of soil leachate, microbial biomass carbon (C), basal respiration, β-1,4-glucosidase activity, β-1,4-N-acetylglucosaminidase activity, bacterial biomass, fungal biomass, total microorganism biomass, and microbial diversity (Shannon diversity index and evenness) were highest at richness level 3. Changes in the microbial community were best explained by variation in the amount and diversity of leachate. Linear regression and correlation analyses indicated that leachate diversity had a close association with microbial Shannon diversity and evenness, whereas leachate amount had a close association with microbial biomass C, total microbial biomass, bacterial biomass, enzyme activities, and abundance of microbial groups. An ordinary least squares multiple regression and the structural equation model demonstrated that leachate amount had a greater effect on microbial biomass than leachate diversity, which had a greater impact on microbial Shannon diversity and evenness. Conclusions: Our results indicate that plant diversity drives changes in soil microbial communities by altering the amount and diversity of leachate in the soil. The diversity of soil leachate determined the diversity of the microbial community to some extent. [ABSTRACT FROM AUTHOR]

• The first study to verify hierarchical traits in microbial biomass, process, and enzyme activity of rhizosphere soils. • Microbial biomass and gas flow in rhizosphere soil of different diameter roots had the similar response to N application. • The changing mechanism of CO 2 , N 2 O, and CH 4 flux were established based on soil chemical property, microbial biomass, and enzyme activity. Root system exhibits hierarchical traits in physiology and exudation, and responds variably to environmental changes. However, it remains unclear if these phenomena result in corresponding alterations in the microbial characteristics of rhizosphere soil and diverse responses to nitrogen (N) deposition. This study evaluated microbial biomass, gas flow, and enzyme activity in rhizosphere soil of three root diameter classes (R1, <0.5 mm; R2, 0.5–1.0 mm; R3, 1.0–2.0 mm) of P. tabuliformis , and their responses to N application (0, 3, 6, 9 g N m−2 y−1, corresponding to CN, LN, MN, and HN) in a P. tabuliformis forest. Rhizosphere soil of R1 exhibited significantly higher microbial biomass N (MBN) content, enzyme activities, CO 2 and N 2 O flow rates than those of R2 and R3 (P < 0.05). Soil microbial biomass carbon (MBC) and phosphorus (MBP) contents, N 2 O and CH 4 flow rates significantly increased with N applications. While soil MBN content increased with the LN treatment and decreased with the HN treatment, the largest value was observed in the LN treatment (84.89 mg kg−1). N application promoted Alkaline phosphatase (ALP) and Alanine transaminase (ALT) activities in R1 rhizosphere soil while decreasing their activities in R2 and R3 rhizosphere soils. Moreover, β-glucosidase (BG), N-acetyl-β-Glucosaminidase (NAG), β-xylosidase (XYL), and β-D-cellulosidase (CBH) activities in R1 rhizosphere soil were inhibited, while their activities in R2 and R3 rhizosphere soils were promoted by N application. N application directly promoted microbial biomass then inhibited enzyme activity. Besides, nutrient content of rhizosphere soil decreased with root diameters, which indirectly reducing enzyme activity and microbial biomass. N application directly affected soil CH 4 flow rate, while N 2 O flow rate was indirectly promoted by N application through increasing microbial biomass. CO 2 and CH 4 flow rates were inhibited by N application through decreasing enzyme activity. Root diameter slowed down the CO 2 and CH 4 flow rates by reducing soil nutrient content and enzyme activity. In conclusion, N deposition has varied effects on microbial characteristics in rhizosphere soil of different diameter roots, which are relevant to the corresponding changes in root system and soil properties. [ABSTRACT FROM AUTHOR]

Research Highlights: Soil enzymes have a significant impact on the production of glomalin-related soil protein (GRSP), directly and indirectly affecting the nutrient metabolism balance, but there is little available information on ecological stoichiometry in soil aggregates. Background and Objectives: Vegetation restoration changes community structure and species composition in ecosystems, thus changing the physicochemical properties of soil. Soil aggregate is the most basic physical structure of the soil. Therefore, in order to understand dynamic changes in soil aggregate nutrients as vegetation restoration progresses, we set out to investigate the nutrient distribution and utilization in aggregates, and how enzymes respond to the nutrient changes in achieving a nutritional balance along successive stages of vegetation restoration. Materials and Methods: We collected and analyzed soil from plots representing six different stages of a vegetation restoration chronosequence (0, 30, 60, 100, 130, and 160 years) after farmland abandonment on the Loess Plateau, China. We investigated soil nutrient stoichiometry, GRSP, and enzyme stoichiometry in the different successional stages. Results: The results revealed that soil organic carbon, total nitrogen, enzyme activity, and GRSP increased with vegetation recovery age, but not total phosphorus, and not all enzymes reached their maximum in the climax forest community. The easily extractable GRSP/total GRSP ratio was the largest at the shrub community stage, indicating that glomalin degradation was the lowest at this stage. Ecological stoichiometry revealed N-limitation decreased and P-limitation increased with increasing vegetation restoration age. Soil enzymes had a significant impact on the GRSP production, directly and indirectly affecting nutrient metabolism balance. Conclusions: Further study of arbuscular mycorrhizal fungi to identify changes in their category and composition is needed for a better understanding of how soil enzymes affect their release of GRSP, in order to maintain a nutrient balance along successive stages of vegetation restoration. [ABSTRACT FROM AUTHOR]

Plant–plant interactions are dynamic and complicated processes that strongly influence soil nutrient cycling in ecosystems. Climate warming-induced drought stress and the duration of plant interactions may reshape or complicate this ecological process. However, little is known about how plant–plant interaction time (co-growth duration) combined with drought stress affect soil chemical properties and enzyme activities. In this study, Stipa bungeana and Bothriochloa ischaemum , which were the main plant species during the later stages of secondary succession in an abandoned cropland on the Loess Plateau of China, were planted as a single plant or in combination, in a plastic pot with two water regimes (ample water, 80 % of field capacity (FC); drought stress, 60 % of FC) for two consecutive years. The rhizosphere soil was collected each year to determine the nutrient contents and enzyme activities, and the microbial metabolic limitations were calculated. We found that plant–plant interactions, drought stress, and sampling year had a significant influence on most rhizosphere soil nutrient contents and enzyme activities. Redundancy analysis showed that soil pH, available phosphorus (aP), and total phosphorus had significant effects on soil enzyme activities in the first year, and soil total nitrogen and aP had significant effects on soil enzyme activities in the second year. Vector analysis indicated that drought stress increased microbial carbon (C) and phosphorus (P) limitation under each planting pattern, and these metabolic limitations showed a decreasing trend in the second year. An structural equation model demonstrated that plant–plant interactions on microbial C and P limitation were larger than drought stress in the first year. Conversely, in the second year, the plant–plant interactions on microbial C and P limitation were lower than that of drought stress. Our findings highlighted that the duration of plant–plant interactions had a significant influence on C flows and nutrient cycling in plant–soil systems, and improved the understanding of plant–plant interactions and drought stress on soil nutrient cycling and microbial metabolic limitations in vegetation restoration ecosystems. • Plant interaction and drought influence rhizosphere nutrient and enzyme activities. • Soil pH, nitrogen, and phosphorus had significant effects on enzyme activities. • Drought stress significantly increased microbial C and P limitation. • Plant interaction duration regulates soil microbial metabolic limitation. [ABSTRACT FROM AUTHOR]

• Planted forest (PF) allocated larger proportion of biomass carbon (C) to belowground than natural forest (NF). • Turning points existed in biomass C allocation along climatic gradient for both PF and NF. • Soil properties had stronger effects on biomass C allocation in PF than NF. Establishing planted forests (PF) by afforestation and naturally regenerating forests (NF) are important measures of enhance carbon (C) sequestration in terrestrial ecosystems. However, the difference of biomass C stocks and allocation between NF and PF and their determinants in water-limited areas remain unclear. To address this gap, we conducted a synthesis of above-ground biomass C (AGBC), below-ground biomass C (BGBC) stocks and root to shoot ratios (R:S) of PF and NF in the Chinese Loess Plateau. The changes in biomass C stock and R:S along a climate gradient were investigated, and the relationships between R:S and soil properties were also quantified. We found that PF exhibited lower AGBC and BGBC stocks compared to NF, but the average R:S in PF was significantly higher than that of NF (0.48 ± 0.27 vs. 0.30 ± 0.11, p < 0.05). Turning points existed in biomass C allocation along climatic gradient for both PF and NF. More biomass C was allocated to AGBC in PF and NF when mean annual precipitation exceeded 494 mm and 588 mm, respectively. Higher mean annual temperature promoted larger C allocations to BGBC in PF compared to NF. Soil properties had a stronger effect on the biomass C allocation patterns after afforestation, but to a lesser extent on NF. This study indicates that afforestation promotes a larger allocation of biomass C into the below-ground compared to naturally regenerated forests, and using the default R:S estimates may result in a severe underestimation of below-ground C stocks in water-limited areas. The biomass C stocks and allocation are collectively determined by climate conditions and soil properties, and accumulated below-ground biomass C stock induced by dryland afforestation may be an important C sink at a broad geographic scale. [ABSTRACT FROM AUTHOR]

• Association between microbial diversity and soil functions was investigated. • Soil potential multifunctionality of alpine meadow decreased along the degradation. • Bacteria rather than fungi are important for soil functions in alpine meadow. • Functional redundancy of microbes may occur in alpine ecosystems. • Bacterial richness is negatively related to potential soil multifunctionality in degraded alpine meadows. Fungal richness and community composition are known to be positively associated with soil multifunctionality. However, the contributions of bacterial and fungal communities to the multiple soil functions of alpine meadow ecosystems have not been widely examined. Here, we surveyed the soil in Qinghai-Tibetan alpine meadows and classified the extent of degradation as undegraded, lightly degraded, moderately degraded, and severely degraded to clarify the associations between microbial diversity (including bacteria and fungi) and potential soil multifunctionality. Bacterial and fungal compositions were detected by sequencing of the 16S rDNA and internal transcribed spacer amplicons, respectively. Functions associated with nutrient cycling (dissolved organic nitrogen and carbon, available phosphorus, NO 3 –, NH 4 +, C, N, P-cycle enzymes) and climate regulation (CO 2 and N 2 O emissions) were also examined. Bacterial, rather than fungal, richness was negatively associated with potential soil multifunctionality, which decreased along the degradation gradient. Structural equation modeling explained 79.6% of the variation in potential soil multifunctionality and confirmed that, in addition to bacterial community richness and composition, organic carbon and moisture were important drivers of potential soil multifunctionality. These results suggest that higher bacterial richness is associated with lower potential soil multifunctionality in alpine meadow ecosystems. Among the bacterial taxa, only ~ 12% of bacterial genera were identified as predictors of multifunctionality, suggesting functional redundancy of the bacterial community in the meadow ecosystem. Rhodanobacter , Mucilaginibacter , Rhodococcus , and Bosea , belonging to the Proteobacteria and the Actinobacteria phyla were identified as critical for maintaining potential soil multifunctionality. Our results suggest that bacterial richness is negatively related to potential soil multifunctionality in alpine meadow ecosystems and there is no correlation between potential multifunctionality and fungal richness. [ABSTRACT FROM AUTHOR]

• Soil C-, N-, and P-acquiring enzyme activities and stoichiometry were investigated. • A non-homeostasis of soil ecoenzymatic activity stoichiometry exists in Tibetan alpine meadows. • Fencing can relieve nutrient limitations by increasing plant biomass. • DOC and microbial biomass N accounted for most variation in ecoenzymatic activity. • Fencing can address microbial nutrient limitations in restoration efforts. The effects of restoration on plant communities and soil nutrients have been extensively studied but knowledge of the metabolic requirements of microbial communities is limited, especially in fragile alpine meadow ecosystems. Here, vegetation and soil from four meadows (grazed meadow, fenced meadow, fenced + reseeded meadow, and undegraded meadow) on the Tibetan Plateau were investigated. The nutrient requirements of microbes represented by stoichiometry of extracellular enzyme activities related to soil C, N, and P acquisition (β-1,4-glucosidase, BG; β-1,4-N-acetylglucosaminidase, NAG; leucine aminopeptidase, LAP; and alkaline phosphatase, AP) and their possible environmental drivers were determined. Our results showed that enzymatic C:N:P acquisition in all the meadows deviated from 1:1:1, suggesting that soil enzymatic activity stoichiometry in Tibetan alpine meadows is not homeostatic. Microbial communities in grazed meadows were co-limited by soil N and P levels, and this limitation was closely associated with the stoichiometry of soil nutrients. Activities of BG, NAG + LAP, AP, and their stoichiometry (C:N, C:P, and N:P) in fenced meadows were 38.2%, 32.9%, 51.2%, 16.8%, 19.5% and 2.3% higher than those in grazed meadows. These results indicate that fencing can relieve the N and P limitations for microbial communities in alpine meadows. Seeding the fenced meadow did not increase the soil nutrient content, microbial biomass, or enzyme activity compared with the fenced meadow, possibly owing to the low competition of the seeded species for resources. Changes in extracellular enzyme activity and stoichiometry were better explained by dissolved organic C and microbial biomass N than by plant or other soil properties. Our results demonstrate the effectiveness of fencing on the restoration of degraded alpine meadows from the perspective of alleviating microbial nutrient limitations. [ABSTRACT FROM AUTHOR]

Forest ecosystem is a complex community, and its soil microbes play a vital role in global matter cycling. However, the patterns of rhizosphere soil microbial characteristics among tree-shrub-grass and their responses to nitrogen (N) deposition are still unclear. This study evaluated the microbial biomasses, processes (gas fluxes), and enzyme activities in the rhizosphere soils of tree (Pinus tabuliformis), shrub (Rosa xanthina), and grass (Carex lanceolata) and their responses to N addition (0, 3, 6, 9 g N m−2 y−1 corresponding to N0, N3, N6, N9) in a P. tabuliformis plantation. (1) Microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP) contents, as well as CO 2 , CH 4 flux rates in the rhizosphere soil of C. lanceolata were significantly higher than those in the rhizosphere soils of P. tabuliformis and R. xanthina (P < 0.05). The activities of alkaline phosphatase (ALT), leucine aminopeptidase (LAP), β-glucosidase (BG), D -cellulosidase (CBH), N-acetyl-glucosaminidase (NAG), and xylosidase (XYL) in the rhizosphere soils of C. lanceolata and R. xanthina were significantly higher than those in the rhizosphere soil of P. tabuliformis. (2) Soil MBC content, N 2 O, and CH 4 flux rates increased after N addition, while the CO 2 flux rate decreased. MBP content initially increased and then reduced with N additions, and the maximum values observed in N3 or N9 treatments. (3) In the rhizosphere soil of P. tabuliformis , N addition enhanced the NAG, BG, CBH, and XYL activities. While low N increased and high N decreased these enzyme activities in the rhizosphere soils of C. lanceolata and R. xanthina , with the maximum values obtained in N3 treatment. (4) N addition directly reduced the CO 2 flux rate and indirectly enhanced the gas flux rate by increasing soil MBC and MBP contents. Species change indirectly affected the microbial biomass and enzyme activity by altering soil chemical properties, which eventually affected gas flux rates. Our study emphasizes the effects of tree-shrub-grass on soil microbial characteristics, which can improve the evaluation of soil ecological processes and responses to N deposition in forest ecosystems. • Rhizosphere soil of understory vegetations had higher microbial biomass, enzyme activity, and gas flow than that of canopy tree. • Nitrogen addition increased soil microbial biomass carbon content, N 2 O and CH 4 flux rates, but decreased CO 2 flux rate. • Enzyme activities in rhizosphere soils of different plant species exhibited varied responses to nitrogen addition in forest plantation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microplastics reduced the infiltration and retention of clay and sand soil water. • Microplastics impacted clay soil with higher organic content more. • Microplastics caused soil pore size and number to decline. • Residual plastics in agricultural soils need to be managed to maintain soil quality. Microplastic pollution and changes to soil hydraulic characteristics affect the physical properties and functions of soil; however, knowledge remains limited on how microplastics influence soil hydraulic properties. Nonetheless, it is important to understand these relationships to maintain soil health and ensure sustainable land use, especially in the current "plastic age." This case study explored how different particle sizes (20, 200, and 500 μm) and concentrations (up to 6%) of polypropylene microplastics affect the hydraulic properties of three soil textures (loam, clay, and sand). The results show that addition of microplastic reduced the saturated hydraulic conductivity (Ks) of the three soils by 69.79%, 77.11%, and 95.79%, respectively. These observed adverse effects of microplastics on the infiltration properties of the three studied soils were influenced by particle size, with larger particles having the weakest effect. Furthermore, microplastic addition reduced the water retention capacity of the clay to a greater extent than that of the loam and sand. In the case of clay, the slope of the water characteristic curve (SWRC) increased significantly, whereas the saturated water content (θs) and residual water content (θr) curves decreased significantly. Importantly, the interaction between microplastics and soil alters the soil pore-size distribution and reduces pore availability. Overall, this case study demonstrates the impact of microplastic on the hydraulic properties of different soil textures, which can inform management strategies to minimize the adverse effects of microplastic accumulation on yields where plastics are used in agricultural production. [ABSTRACT FROM AUTHOR]

• Warming significantly lowered soil nematode diversity. • Warming indirectly and directly affected vegetation to lead to soil nematodes diversity being changed. • Warming and litter removal significantly reduced external resource inputs to the food web. • Warming and litter removal lead to soil food web degradation. Both climate warming and litter removal alter soil nematode communities and the structure, stability, and function of soil food webs. The soil nematode metabolic carbon footprint, based on nematode biomass and respiration, can be used to indicate ecosystem function and the response of nematodes to nutrient enrichment in the ecosystem. However, it is unclear whether or how climate warming and litter removal affect the metabolic carbon footprint of soil nematodes and soil food webs. In this study, we investigated four warming and litter removal treatments in the Qinghai-Tibet Plateau, China, to determine the effects of climate warming and litter removal on soil microbial food webs. The treatments included: (1) control (CK), (2) warming, (3) litter removal, (4) warming + litter removal. We found that warming and litter removal had significant negative effects on the diversity and richness of soil nematodes. In addition, our results showed warming indirectly and directly affected vegetation diversity, thereby altering soil nematode diversity. Vegetation played an important role in the maintenance of soil nematode community diversity. The enrichment and structural footprints reflected nematodes that could respond most rapidly to resource enrichment and those with higher trophic levels in soil food webs, respectively. Overall, warming and litter removal significantly negatively affect the enrichment metabolic footprint, indicating they could significantly reduce the external resource inputs into the food web. Both warming and litter removal reduced the structural metabolic footprint of the soil food web, although the changes were not significant, indicating that the metabolic activity of nematodes of high nutrient levels decreased and the ability to regulate the food web from top-bottom effects was weakened under warming and litter removal. The nematode functional metabolic footprints indicated that litter removal could aggravate the effect of warming on the soil food web and result in more severe degradation. The combination of warming and litter removal significantly inhibited the connectance of the bacterial channel, but had no significant effect on the fungal channel. These results suggest that the soil food web enhanced resistance to the environment by increasing the proportion of the fungal channel. It is critical to understand the responses of soil food webs to climate warming and litter removal to better predict how ecosystem functions will change in the future. [ABSTRACT FROM AUTHOR]

• Soil nematode diversity and abundance increase with vegetation restoration time. • Vegetation restoration time enhances metabolic activity of omnivorous carnivores. • Longer restoration time promotes carbon flow and stabilizes the soil food network. • During land restoration bacteria were more important than fungi in the carbon flow. • Abandoning agriculture can help to avoid soil degradation in the Loess Plateau. Soil nematode communities play a significant role in soil ecosystems. Indeed, soil nematode metabolic carbon footprint, based on nematode biomass, is used to evaluate ecosystem functioning and assess nematode response to ecosystem nutrient enrichment. However, it is unclear whether vegetation restoration affects the metabolic carbon footprint of soil nematodes and soil food webs. We selected five periods for this study including: (1) farmland (0 years), (2) grassland (30 years), (3) shrubland (60 years), (4) pioneer forest (100 years), and (5) climax forest (160 years). Community composition, diversity, and metabolic footprint of soil nematodes, and carbon flow changes through the food web were investigated. The Shannon diversity (H′) index of the soil nematode community increased in the process of restoration, and the Pielou index (J′) appeared to be lower at 30 years after vegetation restoration than at 60, 100, and 160 years. The connectance of the soil nematode food web values increased continuously, from 30 years to 160 years, reaching the highest value at 100 and 160 years, which indicated that the food web had the strongest carbon flow at 100 years after vegetation restoration on the Loess Plateau, indirectly reflecting the stability of the soil food web. Bacteria were more important than fungi in the carbon flow in the food web during vegetation restoration. The study demonstrated that vegetation restoration promoted the input of the availability of external resources, enhanced the metabolic activity of omnivorous carnivores and the soil carbon flow, and stabilized the soil food web. However, the increase in vegetation restoration time not only changed the species composition but also changed the carbon input, due to the lack of interference by agriculture. Therefore, the intrinsic mechanism needs to be studied further. [ABSTRACT FROM AUTHOR]

• Recovery years increased soil microbial activity in the surface layer (0–10 cm) • Recovery years enhanced stratification ratios of rhizosphere soil microbial (SRR 1) • SRR 1 became positive with increased soil microbial activity. Studying soil microbial activity is important for evaluating soil microbial conditions and soil nutrient cycling. This study examined how the conversion of cropland to forest affects soil microbial activity and stratification ratios of the rhizosphere soil microbial index (RSMI), as well as to clarify the relationship between the stratification ratios of RSMI and soil microbial activity. Soils beneath two typical vegetation types of shrubland (Caragana korshinskii and Hippophae rhamnoides) and forestland (Robinia pseudoacacia) in the Loess Hilly region of China that had recovered for up to 47 and 56 years, respectively, were evaluated at four soil depths (0–10, 10–20, 20–30, and 30–50 cm). Our findings showed that the conversion of cropland to forest mainly affected soil microbial activity in the surface layer (0–10 cm), in which microbial biomass, enzyme activity (saccharase, urease, and phosphatase), and RSMI increased over time, whereas the microbial metabolic quotient decreased. After the conversion from cropland, recovery time (years) caused an increase in the SRR 1 (the RSMI ratio in 0–10 cm versus 10–20 cm layer) of shrubland (by 40.56–108.14%, compared to 0 year) and forestland (by 18.48–79.71%, compared to 0 year). Overall, SRR 1 was positively correlated with RSMI in both conversion types. In conclusion, the stratification ratios of the rhizosphere soil microbial index of SRR 1 provided good indicators of soil microbial activity and were significantly enhanced by the process of the conversion from cropland to forest. [ABSTRACT FROM AUTHOR]

• Recovery years increased soil microbial activity in the 0–20 cm soil layers. • Recovery years had smaller effect on soil microbial activity in the 30–50 cm layers. • Factors regulating microbial activity changes were different among the four layers. Cropland abandonment strongly affects plant-soil interactions. However, knowledge remains limited about how the production and diversity of plants and soil physicochemical parameters drive changes in soil microbial activity (such as microbial biomass, respiration, and enzyme activity) after cropland abandonment. Here, we investigated a grassland restoration chronosequence (0–30 years) to determine the dynamics of soil microbial biomass, respiration, and enzyme activity in the Loess Hilly, Region (China). Overall, cropland abandonment caused an increase in soil microbial activity primarily in the 0–20 cm soil layers. The metabolic quotient in the 0–10 cm layer decreased linearly with time since abandonment (recovery years). Structural equation models showed that recovery years directly and indirectly affected changes to soil microbial activity. Plant species richness, aboveground biomass, and soil organic carbon explained a large proportion of the variability in soil microbial activity in the 0–20 cm layer. However, the variability in soil microbial activity was mostly explained by plant species richness, belowground biomass, and soil total nitrogen in the 20–50 cm layers. Our results indicate that during recovery after cropland abandonment, changes in soil microbial activity are driven by plant characteristics and soil physicochemical parameters, with different drivers at different soil depths. [ABSTRACT FROM AUTHOR]

The glomalin-related soil protein (GRSP) is an important fraction of soil organic carbon (SOC) and soil nitrogen (N), and is important for stabilization of SOC and soil aggregates. However, the effects of natural restoration on the concentration and allocation of GRSP differ for different soil aggregate sizes, and how size further affects SOC and soil N restoration, and stabilization of SOC and soil aggregates is not well understood. Here, we present the first characterization of the distribution of GRSP fractions and soil nutrients in soil aggregates following natural restoration by choosing fields of 0, 7, 12, 17, 22, 32 years after cropland abandonment, and a natural grassland as reference. GRSP concentration increased most in microaggregates after 32 years of natural restoration. The processes of rapid accumulation of GRSP (22 to 32 years) occurred simultaneously with the formation of macroaggregates, reduction of microaggregates, and rapid increase of mean weight diameter (22 to 32-years). The soil aggregate stability and contents of GRSP, SOC, labile carbon, total N and phosphorus in each soil aggregate fraction significantly increased in the late stage of natural restoration (22 to 32 years). The most recalcitrant carbon fraction in microaggregates significantly increased between 7 and 32 years (0.887 g kg−1). Our study suggests that abandoning farmland is effective for the restoration of GRSP, soil nutrients and structure and that microaggregates promote the accumulation of recalcitrant carbon and increase the stability of SOC largely through its ability to retain GRSP. • Natural revegetation increased the stability of SOC in aggregates < 2 mm. • Large macroaggregates played an important role in TN, SOC and labile carbon accumulation. • GRSP facilitated the accumulation of SOC and TN, and promoted the increased soil aggregation. • Microaggregates increased recalcitrant carbon and the SOC stability largely by retaining GRSP. [ABSTRACT FROM AUTHOR]