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BackgroundLand use/cover and management practices are widely known to influence soil organic matter (SOM) quality and quantity. The present study investigated the effect of different land use, i.e., forests viz. mixed forest cover (MFC), Prosopis juliflora (Sw.) DC-dominated forest cover (PFC), and cultivated sites viz. agriculture field (AF), vegetable field (VF), respectively, on soil parameter, microbial activity, and enzymes involved in soil nutrient cycle in a semiarid region of India.ResultsThe results showed a significant reduction (P < 0.05) in soil carbon (SC), soil nitrogen (SN) content (~ 30–80%) and consequently the soil microbial biomass carbon (SMBC) (~ 70–80%), soil basal respiration (SBR), soil substrate-induced respiration (SSIR), and soil enzyme activities (β-glucosidase, acid phosphatase, and dehydrogenase) under cultivated sites in comparison with forest sites. Pearson’s correlation showed that a positive correlation of SC with SMBC, SBR, SSIR (P < 0.01), and enzymatic activities (i.e., β-glucosidase, dehydrogenase) (P < 0.05) may imply the critical role of SC in regulating microbial and enzymatic activity. Also, a positive correlation of soil moisture with urease activity (P < 0.01) was found suggesting it as a significant abiotic factor for soil biological functions. Additionally, based on the PCA analysis, we observed the clustering of SMBC/SC ratio and qCO2 nearby AF.ConclusionOur study suggests that soil microbial parameters (SMBC, SBR, SSIR, SMBC/SC, qCO2) and enzyme activity are key indicators of soil health and fertility. Land use/cover alters the SOM content and soil microbial functions. The management strategies focusing on the conservation of natural forest and minimizing the land disturbances will be effective in preventing soil carbon flux as CO2 and maintaining the SC stock.

Plant functional diversity and soil microbial community composition are tightly coupled. Changes in these interactions may influence ecosystem functioning. Links between plant functional diversity, soil microbial communities and ecosystem functioning have been demonstrated in experiments using plant monocultures and mixtures, using broad plant and microbial functional groups, but have not been examined in diverse natural plant communities. We quantified the relative effects of plant and microbial functional properties on key ecosystem functions. We measured plant functional diversity, soil microbial community composition and parameters associated with nitrogen (N) cycling and key nutrient cycling processes at three grassland sites in different parts of Europe. Because plant structure and function strongly influence soil microbial communities, we determined relationships between ecosystem properties, plant traits and soil community characteristics following a sequential approach in which plant traits were fitted first, followed by the additional effects of soil microorganisms. We identified a continuum from standing green biomass and standing litter, linked mostly with plant traits, to potential N mineralization and potential leaching of soil inorganic N, linked mostly with microbial properties. Plant and microbial functional parameters were equally important in explaining % organic matter content in soil. A parallel continuum ran from plant height, linked with above-ground biomass, to plant quality effects captured by the leaf economics spectrum, which were linked with the recycling of carbon (C) and N. More exploitative species (higher specific leaf area, leaf N concentrations and lower leaf dry matter content) and taller swards, along with soil microbial communities dominated by bacteria, with rapid microbial activities, were linked with greater fodder production, but poor C and N retention. Conversely, dominance by conservative species (with opposite traits) and soil microbial communities dominated by fungi, and bacteria with slow activities, were usually linked with low production, but greater soil C storage and N retention. Synthesis – Grassland production, C sequestration and soil N retention are jointly related to plant and microbial functional traits. Managing grasslands for selected, or multiple, ecosystem services will thus require a consideration of the joint effects of plant and soil communities. Further understanding of the mechanisms that link plant and microbial functional traits is essential to achieve this.

• Soil solarization achieved 100% control of Bradysia cellarum. • The initial growth of Chinese chive was lower in solarized than control plots, but 20 d after treatment plants in the solarized had recovered and leaf height and yield were equivalent among the treatments. • Soil microbial community diversity in the treatment group first decreased and then recovered gradually, and abundance of beneficial microorganisms increased significantly. Bradysia cellarum Frey (Diptera: Sciaridae) is an important subterranean pest and is especially damaging to Chinese chive. An effective and more environmentally safe method than pesticides is needed for its control. The efficacy of B. cellarum control, growth of Chinese chive and soil microbial diversity were investigated after uae of soil solarization to exterminate this insect pest. The results show that on the first day after soil solarization 100% control of B. cellarum was achieved. Growth of Chinese chive was lower in solarized plots than in control plots over the first 10 d after treatment. Chive growth in solarized plots increased subsequently to match that in the control plots. Moreover, the soil microbial community diversity in the treatment group decreased initially before gradually recovering. In addition, the abundance of beneficial microorganisms in the genus Bacillus and the phyla Proteobacteria, Chloroflexi and Firmicutes increased significantly. Soil solarization is therefore practical and worthy of promotion in Chinese chive-growing regions.

Intercropping change soil bacterial communities in tea plantations. Intercropping increasing nitrogen cycling in the soils of tea plantations. Intercropping with eco-friendly crops is a well-known strategy for improving agriculture sustainability with benefits throughout the soil community, though the range of crop impacts on soil microbiota and extent of feedbacks to crops remain largely unclear. This study evaluated the impacts of different intercropping systems on soil bacterial community composition, diversity, and potential functions in tea gardens. Intercropping systems were found to be significantly influenced soil microbiota. Within the three tested intercropping systems (tea-soybean, tea-rapeseed and tea-soybean-rapeseed), the tea-soybean-rapeseed intercropping system had the most dramatic influence on soil microbiota, with increases in richness accompanied by shifts in the structure of tea garden soil bacterial networks. Specifically, relative abundance of potentially beneficial bacteria associated with essential mineral nutrient cycling increased significantly in the tea-soybean-rapeseed intercropping system. In addition, soil microbial functions related to nutrient cycling functions were significantly enhanced. This was in accordance with increasing relative abundance of nitrogen cycling bacteria, including Burkholderia spp. and Rhodanobacter spp. Based on these results, it is proposed that intercropping tea plantation with soybean and rapeseed may benefit soil microbiota, and thereby promises to be an important strategy for improving soil health in ecologically sound tea production systems.

Soils, plants, and microbial communities respond to global change perturbations through coupled, nonlinear interactions. Dynamic ecological responses complicate projecting how global change disturbances will influence ecosystem processes, such as carbon (C) storage. We developed an ecosystem-scale model (Stoichiometrically Coupled, Acclimating Microbe-Plant-Soil model, SCAMPS) that simulates the dynamic feedbacks between aboveground and belowground communities that affect their shared soil environment. The belowground component of the model includes three classes of soil organic matter (SOM), three microbially synthesized extracellular enzyme classes specific to these SOM pools, and a microbial biomass pool with a variable C-to-N ratio (C:N). The plant biomass, which contributes to the SOM pools, flexibly allocates growth toward wood, root, and leaf biomass, based on nitrogen (N) uptake and shoot-to-root ratio. Unlike traditional ecosystem models, the microbial community can acclimate to changing soil resources by shifting its C:N between a lower C:N, faster turnover (bacteria-like) community, and a higher C:N, slower turnover (fungal-like) community. This stoichiometric flexibility allows for the microbial C and N use efficiency to vary, feeding back into system decomposition and productivity dynamics. These feedbacks regulate changes in extracellular enzyme synthesis, soil pool turnover rates, plant growth, and ecosystem C storage. We used SCAMPS to test the interactive effects of winter, summer, and year-round soil warming, in combination with microbial acclimation ability, on decomposition dynamics and plant growth in a tundra system. Over 50-year simulations, both the seasonality of warming and the ability of the microbial community to acclimate had strong effects on ecosystem C dynamics. Across all scenarios, warming increased plant biomass (and therefore litter inputs to the SOM), while the ability of the microbial community to acclimate increased soil C loss. Winter warming drove the largest ecosystem C losses when the microbial community could acclimate, and the largest ecosystem C gains when it could not acclimate. Similar to empirical studies of tundra warming, modeled summer warming had relatively negligible effects on soil C loss, regardless of acclimation ability. In contrast, winter and year-round warming drove marked soil C loss when decomposers could acclimate, despite also increasing plant biomass. These results suggest that incorporating dynamically interacting microbial and plant communities into ecosystem models might increase the ability to link ongoing global change field observations with macro-scale projections of ecosystem biogeochemical cycling in systems under change.

1. Arbuscular mycorrhizal fungi (AMF) have been proposed as a mechanism to reduce nutrient inputs in agriculture, thereby reducing costs and increasing environmental sustainability. However, before this can be achieved, we need to gain a better understanding of the importance of the prolonged selective pressures acting on indigenous AMF communities. 2. Much research concentrates on short-term ecological soil x plant x AMF interactions. However, we have little understanding of how long-term manipulations of abiotic conditions can be strong selection agents for AMF communities. Here, we ask how the long-term management of soil fertility and fertilizer use can influence the AM symbiosis. More specifically, we investigated whether 70 years of consistently imposed nutrient limitations affected the structure and symbiotic functioning of indigenous AMF communities. 3. Using the long-term Static Nutrient Deficiency Experiment carried out since 1937 in Thyrow, Germany, with and without nitrogen (N) and phosphorus (P) additions, we addressed the following questions: (i) Do different soil fertilizer treatments affect the overall abundance and diversity of indigenous AMF in an agricultural field; and (ii) Does the depletion of a nutrient select for an enhanced AMF ability to supply the deficient nutrient? 4. We assessed AMF spore diversity in the field and established a common garden experiment where soil nutrient treatments were calibrated against those in the long-term field experiment. For each soil nutrient treatment, we compared the growth responses of barley plants to the indigenous AMF communities isolated from the different soil fertilization treatments in the field. 5. We found that the long-term use of specific soil fertilization treatments altered the effects of the AMF symbiosis on plant and fungal growth. Consistent with the optimal foraging theory, AMF from N-or P-deficient soils grew larger but reduced plant growth more in those conditions relative to AMF isolated from non-deficient soils. This could result from both community-level changes and/or adaptations within species. 6. Thus, we propose that the ongoing agronomic management of abiotic selective pressures such as soil fertility needs to be considered as a strong determinant of AMF symbiotic functioning.

In studying problems like plant‐soil‐microbe interactions in environmental biogeochemistry and ecology, one usually has to quantify and model how substrates control the growth of, and interaction among, biological organisms (and abiotic factors, e.g., adsorptive mineral soil surfaces). To address these substrate‐consumer relationships, many substrate kinetics and growth rules have been developed, including the famous Monod kinetics for single‐substrate‐based growth and Liebig's law of the minimum for multiple‐nutrient‐colimited growth. However, the mechanistic basis that leads to these various concepts and mathematical formulations and the implications of their parameters are often quite uncertain. Here, we show that an analogy based on Ohm's law in electric circuit theory is able to unify many of these different concepts and mathematical formulations. In this Ohm's law analogy, a resistor is defined by a combination of consumers’ and substrates’ kinetic traits. In particular, the resistance is equal to the mean first passage time that has been used to derive the Michaelis‐Menten kinetics under substrate replete conditions for a single substrate as well as the predation rate of individual organisms. We further show that this analogy leads to important insights on various biogeochemical problems, such as (a) multiple‐nutrient‐colimited biological growth, (b) denitrification, (c) fermentation under aerobic conditions, (d) metabolic temperature sensitivity, and (e) the legitimacy of Monod kinetics for describing bacterial growth. We expect that our approach will help both modelers and nonmodelers to better understand and formulate hypotheses when studying certain aspects of environmental biogeochemistry and ecology. Plain Language Summary Currently, scientists often use ad hoc or empirical approaches to conceptualize and formulate biogeochemical processes encountered in environmental sciences. Here, we propose that many biogeochemical processes can be coherently conceptualized and formulated using an analogy based on Ohm's law, a mathematical theory that is widely used to model electric circuits, and the land‐atmosphere exchange of water and energy. We show that this Ohm's law analogy is able to explain observations such as why microbial growth often follows Monod kinetics, how fermentation can sometimes dominate aerobic respiration when glucose is plentiful, and how plants and microbes grow under multiple‐nutrient‐colimitation. Since this Ohm's law analogy unifies the mathematical foundation of biogeophysics and biogeochemistry, we believe that it can potentially lead to more robust land ecosystem models for projecting the climate change. Key Points Ohm's law is proposed to formulate biogeochemical reactions Ohm's law successfully represents multiple‐nutrient‐colimited growth Ohm's law may help improve and unify biogeochemical models

Soil fungi and bacteria are the key players in the transformation and processing of carbon and nutrients in terrestrial ecosystems, yet controls on their abundance and activity are not well understood. Based on stoichiometric principles, soil microbial processes are expected to be limited by mineral nutrients, which are particularly scarce in often highly weathered tropical forest soils. Such limitation is directly relevant for the fate of soil carbon and global element cycles, but its extent and nature have never been assessed systematically across the tropical biome. Here, we address the relative importance of nitrogen, phosphorus, and other nutrients in limiting soil microbial biomass and process rates in tropical forests. We conducted an in-depth literature review and a meta-analysis of the available nutrient addition experiments in tropical forests worldwide. Our synthesis showed predominant and general phosphorus limitation of a variety of microbial processes across tropical forests, and additional nitrogen limitation in tropical montane forests. The apparent widespread microbial phosphorus limitation needs to be accounted for in the understanding and prediction of biogeochemical cycles in tropical forests and their future functioning. Other mineral nutrients or carbon may modify the importance of phosphorus, but more experimental studies are urgently needed.

Intensive crop production on grassland-derived Mollisols has liberated massive amounts of carbon (C) to the atmosphere. Whether minimizing soil disturbance, diversifying crop rotations, or re-establishing perennial grasslands and integrating livestock can slow or reverse this trend remains highly uncertain. We investigated how these management practices affected soil organic carbon (SOC) accrual and distribution between particulate (POM) and mineral-associated (MAOM) organic matter in a 29-y-old field experiment in the North Central United States and assessed how soil microbial traits were related to these changes. Compared to conventional continuous maize monocropping with annual tillage, systems with reduced tillage, diversified crop rotations with cover crops and legumes, or manure addition did not increase total SOC storage or MAOM-C, whereas perennial pastures managed with rotational grazing accumulated more SOC and MAOM-C (18 to 29% higher) than all annual cropping systems after 29 y of management. These results align with a meta-analysis of data from published studies comparing the efficacy of soil health management practices in annual cropping systems on Mollisols worldwide. Incorporating legumes and manure into annual cropping systems enhanced POM-C, microbial biomass, and microbial C-use efficiency but did not significantly increase microbial necromass accumulation, MAOM-C, or total SOC storage. Diverse, rotationally grazed pasture management has the potential to increase persistent soil C on Mollisols, highlighting the key role of well-managed grasslands in climate-smart agriculture.

Modern conceptual models of soil organic carbon (SOC) cycling focus heavily on the microbe-mineral interactions that regulate C stabilization. However, the formation of ‘stable’ (i.e. slowly cycling) soil organic matter, which consists mainly of microbial residues associated with mineral surfaces, is inextricably linked to C loss through microbial respiration. Therefore, what is the net impact of microbial metabolism on the total quantity of C held in the soil? To address this question, we constructed artificial root-soil systems to identify controls on C cycling across the plant-microbe-mineral continuum, simultaneously quantifying the formation of mineral-associated C and SOC losses to respiration. Here we show that root exudates and minerals interacted to regulate these processes: while roots stimulated respiratory C losses and depleted mineral-associated C pools in low-activity clays, root exudates triggered formation of stable C in high-activity clays. Moreover, we observed a positive correlation between the formation of mineral-associated C and respiration. This suggests that the growth of slow-cycling C pools comes at the expense of C loss from the system. Root exudates can either promote or impede the formation of stable, mineral-associated soil organic carbon (MAOC). Yet, carbon stabilisation in MAOC is decoupled from changes in the total soil carbon pool, i.e., carbon sequestration.