Conservation agriculture (CA) has long been recognized as a promising method to enhance soil health and sustain agricultural productivity, particularly via its increasingly acknowledged efficacy in pest management. Nevertheless, scientific consensus on its efficacy remains under debate. Using a global meta-analysis of 925 maize field trials combined with Gradient Boosting Regression Tree (GBRT) modeling, we demonstrate that CA practices significantly curtail pest populations and associated crop damage, simultaneously promoting natural enemy abundance and maintaining crop yields. Among CA practices, crop diversification proves most effective for integrated pest management while maintaining agricultural productivity, provided it is implemented within a well-designed agroecosystem framework. CA has the strongest influence on pest control in warm-moist climates and moderate-fertility soils. Moreover, the GBRT model identifies total soil nitrogen, companion crop type, and soil texture as the three most critical factors influencing pest and natural enemy dynamics in maize fields. Predictions reveal that CA adoption could reduce maize field pest abundances by 10.91% and elevate their natural enemy populations by 3.82% worldwide, with this efficacy further amplified under moderate to severe future warming scenarios. This study provides the first global-scale evidence that CA can enhance pest suppression in maize agroecosystems and underscores its pivotal role in climate-resilient sustainable agricultural production.

Microbial death pathways (MDPs) are increasingly recognized as key drivers of terrestrial carbon cycling, primarily through their regulation of microbial necromass carbon (MNC), a critical pool in global carbon dynamics. Yet explicit representation of MDPs in soil organic carbon (SOC) models remains limited. Here, we developed and evaluated three SOC models that differ in their structure of MNC pool: the multiple-pathway necromass (MPN) model, which partitions microbial necromass carbon (MNC) into four MDP-derived subpools; the dual necromass (DUN) model, which differentiates two necromass pools with distinct decay rates; and the single necromass (SIN) model, which aggregates necromass into a single pool. Using a unified data assimilation framework and SOC observations from six major agricultural regions in China, we found that the MPN model consistently outperformed DUN and SIN models across most regions, producing necromass subpool dynamics, scenario responses, and parameter sensitivities that closely reflect the mechanistic understanding of MDPs. In cold or nutrient-limited regions, however, the simpler DUN model performed similarly while requiring fewer parameters, emphasizing the importance of balancing model complexity with regional ecological constraints. Our results demonstrate that explicitly incorporating MDPs enhances the robustness and mechanistic realism of SOC simulations and provides a robust foundation for more explicit representations of MDPs to assess the soil carbon sequestration potential and guide sustainable land management.

Soil microbial network complexity and stability are fundamental to ecosystem functioning, yet their interdependence across agricultural practices remains poorly understood. This study investigates long-term (>10 years) tillage (no-tillage [NT] vs. conventional tillage [CT]) and cropping systems (maize (Zea mays L.)-soybean (Glycine max Merr.) rotation [MS] vs. continuous maize [MM]) effects on bacterial network complexity and stability across soil layers (0-5 cm and 5-20 cm) in the black soils of northeastern China. High-throughput sequencing and cohesion-based network analysis were used to assess microbial interactions, complexity as the sum of absolute cohesion values, and stability as the ratio of negative to positive cohesion. Results revealed depth-dependent trade-offs between bacterial network complexity and stability. Compared to CT, NT increased complexity at 0-5 cm (2.13%) but reduced it at 5-20 cm (-2.69%), where stability improved (2.20%). Compared to MM, MS decreased complexity at both depths (0-5 cm: -2.11%; 5-20 cm: -3.94%) and improved stability at 5-20 cm (1.84%). Maximum complexity occurred under NTMM (no-tillage with continuous maize cropping) (0-5 cm) and CTMM (conventional tillage with continuous maize cropping) (5-20 cm), whereas stability was greatest under NTMS (no-tillage with maize-soybean rotation) (5-20 cm). A significant negative correlation between complexity and stability was detected at both depths (r = -0.38 at 0-5 cm; r = -0.75 at 5-20 cm), supporting the "complexity-stability paradox" in soil ecosystems. These findings underscore that trade-offs between microbial network complexity and stability are shaped by the interaction of agricultural practices and soil depth. Tailoring tillage and crop rotation strategies to influence specific soil depth zones is crucial for enhancing microbial resilience and sustaining long-term soil health.

In Northeast China, conventional tillage practices involve removal of crop residue after harvest and prior to moldboard plowing; this has been shown to cause a decline of soil organic carbon (SOC) and degradation of Black soils (Mollisols). Conservation tillage, particularly no tillage (NT), has been suggested to be an effective practice to control soil erosion and increase the SOC content. Hence, we established an experiment (since 2001) to evaluate how a combination of different tillage and cropping systems could improve SOC in black soils. The total SOC storage, SOC fractions (physical and chemical), SOC stability were assessed to evaluate the effects of tillage and cropping system. Our results shows that: 1) different tillage and cropping system combinations had different effects on SOC storage; NT combined with continuous maize had the highest SOC storage among all treatments; 2) The effects of tillage on aggregate size and OC concentration mainly occurred in the surface layer (0–5 cm) while the effect of cropping system on aggregate size and OC concentration mainly occurred at deeper depths; 3) NT increased the recalcitrant carbon pool in surface layer showing the critical need for returning crop residues to maintain long-term SOC storage; 4) SOC mineralization (biological stability) appears to be related to the SOC proportion in the light fraction; 5) More than half of the increase in SOC storage due to NT existed as microbial necromass carbon storage under continuous maize which was higher than maize-soybean rotation. Our study shows that in black soils (Northeast China), NT and appropriate cropping systems can not only halt soil degradation caused by poor management but can induce substantial increases in SOC which is beneficial for SOC long-term sequestration.

Exploring the dynamics of soil carbon (C) response to multi -faceted global climate change plays a vital role in facilitating the estimation of carbon -climate feedback. However, the direction and extent of the warming effect on soil carbon pool within different soil fractions considered simultaneously in increased precipitation and decreased precipitation system are not well understood. Here we established a 2 -year field manipulation experiment based on open top chamber (OTC) to assess the effects of warming and altering precipitation regimes (40 % reduction, normal, and 40 % increment) on soil physical fractions formation and distribution. Our results showed that in the precipitation increment, warming significantly increased particulate organic carbon (POC) and mineral -associated carbon (MAOC) by an average of 48.10 % and 21.28 % in the 0-5 cm soil layer. And the formation mechanism of POC and MAOC were different. POC was directly affected by the coupling between plant input and C -degradation fungal functional genes adjusted by dissolved organic carbon (DOC) and total nitrogen (TN); and MAOC was affected by increasing labile carbon inputs (such as DOC) of maize residue and belowground biomass. However, precipitation reduction neutralized the beneficial effects of warming, mainly through reducing plant inputs and residue decomposition, thereby suppressing C -degradation fungal functional genes and labile carbon supply. Overall, our results provide new insights into the potential mechanisms through which interaction of warming and altered precipitation controls soil C dynamics.

Understanding soil biodiversity response to land use change is crucial for predicting and preserving soil ecological functions and health under anthropogenic influence. Yet, the overall effect of land use changes and climate conditions on belowground biodiversity remains insufficiently explored at large scales. Here, we studied the effect of conversion from natural soils to agricultural soils on soil nematode diversity and community assembly across the Mollisol zone in northeast China. We found that nematode alpha diversity decreased in agricultural soils, and nematode alpha diversity did not exhibit a regular change with latitudinal variation. For beta diversity, we found that nematode community structures were significantly affected by land use change. Furthermore, climatic factors and geographic distance significantly impacted the beta diversity of soil nematodes, but not the alpha diversity. Mean annual temperature was a primary climatic determinant of soil nematode communities, while the effect of mean annual precipitation on soil nematode beta diversity was only observed in agricultural soils. Stochastic processes dominated soil nematode community assembly, but agricultural soils increased the importance of deterministic processes compared to natural soils. There is no any expected variation in soil nematode alpha diversity along the Mollisol zone. Our findings highlight the crucial role of temperature in driving soil nematode communities.

Soil salinization seriously affects soil microbial diversity, and crop yield and quality worldwide. Microorganisms play a vital role in the process of crop yield and quality. Traditional Chinese medicine Glycyrrhiza uralensis Fisch. (licorice) can grow tenaciously in the heavily salinized land. However, the relationship between licorice plants and soil microorganisms is not clear. A field experiment was carried out to explore the effects of three different degrees of salinized soils on (i) licorice crop performance indicators, (ii) soil physical and chemical properties, and (iii) the changes in soil bacterial community structure and functional diversity in a semi-arid area of northwest China. The results showed that with the aggravation of soil salinization, the licorice yield, soil nutrients, and the bacterial abundance of Gemmatimonadetes and Myxococcota showed a downward trend, while the concentration of glycyrrhizic acid and liquiritin, and the bacterial abundance of Actinobacteria and Firmicutes showed an upward trend. The change of licorice yield mainly depended on the soil physical and chemical properties (e.g., EC and alkaline hydrolysable nitrogen). The change of licorice quality was more closely related to the change of bacterial diversity. The effect of bacterial diversity on liquiritin was greater than that on glycyrrhizic acid. Among them, Gemmatimonadetes were significantly negatively correlated with liquiritin and glycyrrhizic acid. These findings suggest that the increased soil Actinobacteria and Firmicutes or reduced Gemmatimonadetes and Myxococcota may provide a healthy and suitable living condition for the sustainable development of medicinal plant crops in a salinized soil ecosystem.

The soil organic carbon (SOC) cycle is dynamic and exhibits both addition of new carbon and consumption of existing SOC; carbon inventory in the soil is the net result of these two opposing processes. Quantifying the residue-derived carbon (RDC) under different tillage systems via 13C tracing technique provides an objective appraisal of the contribution of returned residue to soil carbon sequestration in bulk soil and different fractions. We used 13C-labelled maize residue to monitor the fate of RDC stock (RDCstock) in different soil fractions under no-tillage (NT) and mouldboard ploughing (MP). Accumulation of RDC increased in the surface layer under NT while it decreased in all layers under MP over time. After two years, both NT and MP stored an equivalent amount of RDCstock with a RDCconversion rate of 16.8-17.0 %. Tillage had no effect on the RDC concentration (RDCcon) in microaggregate (Mic), silt-clay (Si-Cl), labile organic carbon (LP-C) and recalcitrant carbon (RP-C), but affected the RDCconin macroaggregate (Mac) and particulate organic carbon (POC). NT generated more RDCstock in Mac than MP, which was induced by the higher RDCstock in coarse particulate organic matter (cPOM) and occluded silt-clay (O-Si-Cl). The percentage of RDCstock in mineral-associated organic carbon (MAOC) contributed more to total RDCstock than POC in both NT and MP, but RDCstock in POC was higher in NT (47 %) than MP (18 %). Most (70 %-75 %) of RDCstock existed as LP-C in both tillage practices. Our results showed that although the total RDCstock reached the same status in both NT and MP, the distribution in soil fractions varied, especially in physical fractions. RDC reached 10-20 cm in NT through leaching and was stored in MAOC, and NT provided strong protection for newly derived carbon via macroaggregates. It also inferred that tillage practices strongly affected the way that newly derived carbon was stored.

Context or problem: Animal manure is an excellent renewable source of plant nutrients, but the correct quantification of nutrient equivalents is affected by manure type and application rate as well as weather conditions that impact crop yields Objective or research question: The objectives from a 32-year field experiment were to (1) compare the effects of mineral N fertilization and solid dairy cattle manure on corn grain yield; (2) determine the manure N fertilizer replacement value (NFRV), and (3) quantify environmental factors, mainly the impact of total precipitation during the critical period (silking) on corn yield and manure NFRV. Methods: A field experiment under continuous corn with annual manure application was conducted over 32 years in Ottawa, Ontario, Canada. Corn yield data were categorized into low, intermediate, and high N response groups. Results: On an equivalent amount of manure organic N basis, NFRVs were, on average, 0.38 (+/- 0.02) for stockpiled manure (SM) and 0.27 (+/- 0.02) for incompletely composted or rotted manure (RM), with a wide range of 0.12 (+/- 0.02), 0.28 (+/- 0.02), and 0.37 (+/- 0.04) for RM, and 0.16 (+/- 0.04), 0.39 (+/- 0.03), and 0.48 (+/- 0.04) for SM under the low, intermediate, and high N response conditions, respectively. Supplementing 100 kg synthetic fertilizer N ha-1 in low RM (50 Mg ha-1 fresh weight; f.w.), and 50 kg fertilizer N ha-1 in high RM (100 Mg ha-1 f.w.) application rates decreased NFRVs under low and intermediate N response conditions, whereas the addition of similar synthetic N in the corresponding SM rates reduced NFRVs only under low N response conditions. Conclusions: Based on the 32-year long-term study, we documented that the maximum economic synthetic N fertilizer rates for continuous corn cropping varied from 117 to 179 kg N ha-1 under the low N response, from 127 to 283 kg N ha-1 under the intermediate N response, and from 227 to 289 kg N ha-1 under the high N response conditions. The NFRVs of solid cattle manures varied according to corn yield-N response levels. Implications or significance: Our findings showed that the response of corn yields to manure NFRV depends on the level of yield-N response and climatic conditions. It also indicated the importance of soil organic amendments for improving the climate resilience of corn production, while simultaneously meeting the demand for more sustainable nutrient management of soil resources.

This paper examines the development of ecological indices for soil nematodes from the perspective of functional traits. It emphasizes the increasing significance of integrating multiple functional traits to achieve a more accurate assessment of soil health. Ecological indices based on life history strategies, feeding habits, and body size provide useful tools for assessing soil health. However, these indices do not fully capture the dynamics of energy flow across multiple-trophic levels in the soil food web, which is critical for a deeper understanding of the intrinsic properties of soil health. By combining functional traits such as functional group, body size, feeding preference and metabolic rate, nematode energy flow analyses provide a more comprehensive perspective. This approach establishes a direct correlation between changes in the morphology, physiology, and metabolism of soil organisms and alterations in their habitat environment. We conducted comparative analyses of the sensitivity of nematode metabolic footprints and energy flow to latitudinal variation using a nematode dataset from the northeastern black soil region in China. The findings suggest that energy flow analyses are more sensitive to latitude and have greater potential to reveal soil health and ecosystem function. Therefore, future research should prioritize the development of automated and efficient methods for analyzing nematode traits. This will enhance the application of energy flow analyses in nematode food webs and support the development of sustainable soil management and agricultural practices.

The biological degradation of plant residues in the soil or on the soil surface is an integral part of the natural life cycle of annual plants and does not have adverse effects on the environment. Crop straw is characterized by a complex structure and exhibits stability and resistance to rapid microbial decomposition. In this study, we conducted a microcosm experiment to investigate the dynamic succession of the soil microbial community and the functional characteristics associated with lignocellulose-degrading pathways. Additionally, we aimed to identify lignocellulose-degrading microorganisms from the straw of three crop species prevalent in Northeast China: soybean (Glycine max Merr.), rice (Oryza sativa L.), and maize (Zea mays L.). Our findings revealed that both the type of straw and the degradation time influenced the bacterial and fungal community structure and composition. Metagenome sequencing results demonstrated that during degradation, different straw types assembled carbohydrate-active enzymes (CAZymes) and KEGG pathways in distinct manners, contributing to lignocellulose and hemicellulose degradation. Furthermore, isolation of lignocellulose-degrading microbes yielded 59 bacterial and 14 fungal strains contributing to straw degradation, with fungi generally exhibiting superior lignocellulose-degrading enzyme production compared to bacteria. Experiments were conducted to assess the potential synergistic effects of synthetic microbial communities (SynComs) comprising both fungi and bacteria. These SynComs resulted in a straw weight loss of 42% at 15 days post-inoculation, representing a 22% increase compared to conditions without any SynComs. In summary, our study provides novel ecological insights into crop straw degradation by microbes.

CONTEXT: Conservation tillage plays a positive role in restoring degraded cropland in terms of increasing carbon sequestration, improving soil aggregation, and maintaining crop productivity. Assessing the key indicators of environment, energy, and economy under different tillage practices could provide a comprehensive scientific basis to implement low-carbon emission, clean and sustainable agricultural management, especially in the longterm experiment field. OBJECTIVE: Our objectives were: 1) to compare crop production under different long-term tillage practices, 2) to evaluate the carbon footprint (CF), energy budget, and net ecosystem economic benefit (NEEB) of spring maize production under different long-term tillage practices. METHODS: Three tillage practices consisting of conventional tillage with complete removal of residue (CT), moldboard plowing with residue return (MP) and no-tillage with residue return (NT), had been conducted for eight years. Greenhouse gas (GHG) emissions from the soil were measured, and the inputs of raw materials and outputs of crop production were also recorded. CF, energy budget, and NEEB were evaluated for two consecutive growing seasons based on the life cycle assessment (LCA) approach. RESULTS AND CONCLUSIONS: Compared with CT, NT could reduce N2O emissions and absorb more CH4, whereas MP significantly increased CO2 emissions from soil. However, there was no significant difference in maize yield among all treatments. Moreover, NT led to both the lowest GHG emissions from soil (GWPGHG) and agricultural inputs (AIGHG), thus NT decreased CF by approximately 40% compared to CT for maize production. Furthermore, MP and NT decreased 8.4% and 35.7% of the energy inputs owing to lower diesel fuel consumption in comparison with CT, yet there was no significant difference in energy output among different tillage practices. The same was true in NEEB, although MP and NT showed lower investments during maize production. These results indicated NT required the lowest energy and financial investment for the same maize yield. In conclusion, NT could minimize CF and energy inputs while insuring maize production from a long-term perspective. Longterm NT can be implemented in Northeast China and similar agro-eco-regions around the world. SIGNIFICANCE: The findings of our study provide scientific data on the performance of different long-term tillage practices in the environment, energy budget and economic benefits. Meanwhile, it also helps to clarify the role of agricultural systems in achieving carbon neutrality and saving energy.

Soil amendments have been proposed as an effective way to enhance soil carbon stocks on degraded soils, particularly in dryland farming areas. Soil organic carbon (SOC) plays an important role in improving soil quality, and soil aggregates are known to be crucial in sequestering and protecting SOC. However, how aggregation and protection of SOC by aggregates respond to a single application of bentonite combined with maize straw remains unknown, especially in the sandy soil of a semi-arid region. A three-year field experiment with four treatments [no amendment (CK), maize straw amendment addition only (T1, 6 Mg ha−1), bentonite amendment addition only (T2, 18 Mg ha−1), and maize straw combined with bentonite amendment (T3, 6 Mg ha−1 maize straw plus 18 Mg ha−1 bentonite)] was conducted in the Loess Plateau of China to assess the effects of bentonite and maize straw on aggregation and SOC. The results indicated that soil bulk density decreased by 2.72–5.42%, and soil porosity increased by 3.38–8.77% with three years of T3 application, especially in the 20–40 cm layer, compared with CK. T3 increased the amount of C input, SOC stock, and SOC stock sequestration rate by 1.04 Mg ha−1 y−1, 0.84–1.08 Mg ha−1, and 0.49 Mg ha−1 y−1, respectively, and it increased the mass proportions and aggregate-associated C stock of >0.25 mm aggregates by 1.15–2.51- and 1.59–2.96-fold compared with CK. Correlation analysis showed a positive correlation of total SOC stock with the C concentration of >2 mm, 0.25–2 mm, and 0.053–0.25 mm aggregates. Aggregates of various sizes in sandy soils have the potential for greater SOC stock. Our findings suggest that the application of maize straw (6 Mg ha−1) combined with bentonite (18 Mg ha−1) would be an effective management strategy to enhance the bulk soil C pools by improving the soil structure and thereby improving soil fertility.

With recent increases in energy costs, information on energy inputs is becoming a more important aspect in management decisions on selection of crop production systems. The effects of long-term (45-55 years) monocropping, rotation cropping, and fertilization on tillage energy (implement draft and tractor fuel consumption) were determined for a Brookston clay-loam soil in southwestern Ontario, Canada. Treatments included fertilized and unfertilized monocrop (continuous) corn (Zea mays L.), and a four year fertilized and unfertilized corn - oat (Avena sativa L.) - alfalfa (Medicago sativa L.) - alfalfa rotation with all phases of the rotation present in each year. The corn and second year alfalfa plots were moldboard plowed each fall after crop harvest, and then spring-tilled (disc, harrow) prior to planting; oat and first year alfalfa plots were not fall plowed or spring-tilled. Moldboard plow draft and tractor fuel consumption were measured annually from 2004 to 2014 using an instrumented tractor and the same plow and settings. Monocrop unfertilized corn consistently exhibited the greatest plow draft and tractor fuel consumption. Draft averaged over ten years was 13.0% higher for unfertilized than fertilized rotation corn, and 15.5% higher for fertilized than unfertilized second year alfalfa; fuel consumption was 10.4% higher for unfertilized than fertilized rotation corn and 5.1% higher for fertilized than unfertilized second year alfalfa. These differences were attributed to treatment-induced changes in soil strength. Both plow draft and fuel consumption were lower in rotation corn relative to monocrop corn, while plow draft was greater in fertilized alfalfa relative to unfertilized alfalfa due to greater root growth. This study demonstrated that long-term cropping systems can have substantial impacts on the energy required for tilling a clay loam soil.

Understanding soil biodiversity response to land use change is crucial for predicting and preserving soil ecological functions and health under anthropogenic influence. Yet, the overall effect of land use changes and climate conditions on belowground biodiversity remains insufficiently explored at large scales. Here, we studied the effect of conversion from natural soils to agricultural soils on soil nematode diversity, community assembly, and the potential relationship between nematode diversity and soil nutrient cycling across the Mollisol zone in northeast China. We found that nematode alpha diversity decreased in agricultural soils, and nematode alpha diversity did not exhibit a regular spatial pattern. For beta diversity, we found nematode community structures were significantly affected by land use change. Furthermore, climatic factors and geographic distance significantly impacted the beta diversity of soil nematodes, but not the alpha diversity. Temperature was a primary climatic determinant of soil nematode communities, while the effect of precipitation on soil nematode beta diversity was only observed in agricultural soils. Stochastic process dominated soil nematode community assembly, but agricultural soils increased the importance of deterministic process compared to natural soils. A partial least squares path model revealed that land use conversion and temperature can indirectly impact soil nutrient cycling by regulating nematode beta diversity. Our study reveals unexpected variation in soil nematode alpha diversity along the Mollisol zone, and highlights the crucial role of nematode beta diversity in maintaining soil nutrient cycling accompanying land use conversion and climate change.

Conservation tillage as an effective alternative to mitigate soil degradation has attracted worldwide attention, but the influences of conservation tillage on soil microbial community and especially function remain unclear. Shotgun metagenomics sequencing was performed to examine the taxonomic and functional community variations of black soils under three tillage regimes, namely no-tillage with residue (maize straw) return (NTS), moldboard plow with residue return (MPS), and moldboard plow without residue return (MPN) in Northeast China. The results revealed: 1) Soil bacterial and archaeal communities differed significantly under different tillage regimes in contrast to soil fungal community. 2) The overlay of less tillage and residues return under NTS led to unique soil microbial community composition and functional composition. Specifically, in contrast to other treatments, NTS increased the relative abundances of some taxa such as Bradyrhizobium, Candidatus Solibacter, and Reyranella, along with the relative abundances of some taxa such as Sphingomonas, Unclassified Chloroflexi and Nitrososphaera decreased; NTS had a unique advantage of increasing the relative abundances of genes involved in 'ATP-binding cassette (ABC) transporters' and 'quorum sensing (QS)' pathways, while MPN favored the genes involved in 'flagellar assembly' pathway and some metabolic pathways such as 'carbon' and 'glyoxylate and dicarboxylate' and 'selenocompound' metabolisms. 3) Significantly different soil bacterial phyla (Acidobacteria, Gemmatimonadetes, and Chloroflexi) and metabolic pathways existed between MPN and another two treatments (NTS and MPS), while did not exist between NTS and MPS. 4) Dissolved organic carbon (DOC) and soil bulk density were significantly affected (P < 0.05) by tillage and accounted for the variance both in microbial (bacterial) community structure and functional composition. These results indicated that a change in tillage regime from conventional to conservation tillage results in a shift of microbial community and functional genes, and we inferred that residue return played a more prominent role than less tillage in functional shifts in the microbial community of black soils.

Rock-Eval pyrolysis has been applied to soil analysis over the past twenty years but still needs more study in diverse land-use and soil types. The linkage between Rock-Eval parameters and those of other soil organic carbon (SOC) analytical methods also needs further research. Our objective of this study was to evaluate the i) effects of tillage and cropping systems on Rock-Eval parameters, ii) the relationship between Rock-Eval parameters and microbial residues, and iii) effectiveness of Rock-Eval analysis in characterizing soil heterotrophic respiration. Samples were collected from a long-term field study in a black soil under tillage systems in Northeast China; the treatments included: a) no tillage with maize (Zea mays L.)-soybean (Glycine max Merr.) rotation (NTMS); b) moldboard plowing with maize-soybean rotation (MPMS); c) no tillage with continuous maize (NTMM); d) moldboard plowing with continuous maize (MPMM); e) conventional tillage with continuous maize (CTMM). Except for CTMM, all crop residues were returned to the soil after harvest. Thermal stability was analysed by Rock-Eval pyrolysis, soil heterotrophic respiration was determined by a bioassay and microbial residues were determined by measuring amino sugars. TMAX (temperature at which the maximum rate of hydrocarbons is released during pyrolysis), T50 (temperature at which 50% of the hydrocarbons are released), HI (hydrogen index), PC/SOC (pyrolysable C/SOC), and ROC/SOC (residual carbon) were estimated from analysis by Rock-Eval. Tillage affected most of the Rock-Eval parameters, while cropping system had little or no effect. Except OIRE6, tillage affected all Rock-Eval parameters in the 0-5 cm layer including TMAX, HI, T50, PC/SOC and ROC/ SOC. The higher TMAX, T50 and HI in NT than MP indicated that residue return and less soil disturbance by tillage increased SOC thermal stability. The HI index showed a strong positive relationship with heterotrophic respi-ration but weakened with increasing incubation time, which showed that Rock-Eval parameters better repre-sented the heterotrophic respiration in the short-term, rather than long-term (>100 days). The strong relationship between TMAX and GluN (glucosamine) observed in this study suggests NT enriches the fungal necromass as stable soil C, which contributes to long-term C sequestration.

Residue return has a profound effect on soil total nitrogen (STN) content and thereby the global soil N cycle. However, a specific understanding of the key factors influencing STN changes after residue return is currently lacking. A meta-analysis of 502 comparisons from China based on 152 published papers was performed to quantify the changes in STN after residue return and assess the effect sizes of the predictor variables. Results showed that residue return significantly increased STN in 0-20 cm by 11.1% compared to no residue return. The STN accumulation accompanying return of crop residues was greater in areas with higher latitude (>40 degrees), lower rainfall (<700 mm) and lower average annual temperature (<5 degrees C) such as in Northeast China. Crop management, climatic factors, soil properties, residue management and fertilizer addition all significantly affected STN after residue return. Land use and mean annual precipitation (MAP) were the most influential predictors of the changes in STN following residue return. The results of structural equation model showed that the duration of residue return, the amount of residue, and the initial STN content of the soil had direct effects on final STN following residue return. In particular, the initial STN content both directly affected the changes in STN and was a transitional factor indirectly affecting changes in STN influenced by MAT, MAP and N fertilizer addition. More generally, land use, climatic attributes, the duration of residue return and the initial STN content are important aspects which should be given more consideration in the process of developing management strategies for returning residue.

Quantifying the potential of soil carbon (C) mineralization improves our understanding of changes in soil health in agricultural ecosystems. Previous studies rarely linked the trait of interactions inherent in soil communities to soil C mineralization rate (C-min). This study provides field-based evidence of tillage-driven changes in biological associations and their impacts on soil Cmin. Data obtained from a long-term (15 years) conservation tillage field experiment in Northeast China, and showed that the soil C-min (per unit soil mass) and specific C-min (per unit soil C) were 79% and 33% higher in topsoil (0-5 cm) and 27% and 24% lower in subsoil (5-20 cm) under no tillage with residue (NT) compared to conventional tillage with residue removal (CT). Meanwhile, in topsoil, NT strengthened biotic associations in June and August; in subsoil, a more complex network was found in CT. In topsoil, soil C-min was not related to soil biotic associations, but was positively (P < 0.05) correlated with soil organic C (SOC) and certain biotic properties (e.g., MBC (microbial biomass carbon), microbial phospholipid fatty acid (PLFA) biomass and the relative abundance of AMF (arbuscular mycorrhizal fungi) and PP (plantparasites)). Among them, the increases in SOC under NT exerted a positive effect on soil C-min directly or indirectly through mediating biotic biomass properties (MBC, the PLFA biomass of all microbial groups and BF biomass). In contrast, in subsoil, soil C-min was positively (P < 0.05) correlated with soil biotic associations, SOC and the relative abundance of PP. Notably, the increase in soil C-min value was mainly achieved by strengthening biological associations. These findings provide novel insights into the role of soil biota in C mineralization, highlighting the diverse mechanisms underlying soil C-min in response to tillage systems at different soil depths.

The biodegradability of soil organic carbon (BSOC), defined as soil mineralization C per unit of soil organic carbon (SOC), is considered to be an important indicator of SOC stability and is closely related to the global C cycle. However, the magnitude and driving mechanism of BSOC in farmland remain largely unexplored, especially at the regional scale. Here, we conducted regional scale sampling to investigate latitude distribution pattern of BSOC and the relative contributions of biotic (soil micro-food web) and abiotic (climate and soil) drivers to BSOC in the black soil region of Northeast China. Results showed that BSOC declined with increasing latitude, which indicates that as the latitude increases, SOC becomes more stable in the black soil region of Northeast China. Over a range of latitude from 43°N to 49°N, BSOC was negatively correlated with soil micro-food web metrics of diversity (indicated by species richness), biomass and connectance, and soil factors of soil pH and clay content (CC), while it was positively correlated with climate factors of mean annual temperature (MAT), mean annual precipitation (MAP) and soil factor of soil bulk density (SBD). Among those predictors, soil micro-food web metrics were the most direct factors contributing to the variations of BSOC, which exerted the largest total effect on BSOC (-0.809). Collectively, our results provide convincing evidence that soil micro-food web metrics play a direct vital role in determining the distribution pattern of BSOC over a range of latitudes in the black soil region of Northeast China. This highlights the necessity of considering the role of soil organisms in regulating C dynamics in prediction of SOC mineralization and retention in the terrestrial ecosystem.