Dissolved organic matter (DOM) is involved in numerous biogeochemical processes, and its molecular weight affects many of these processes through its bioavailability and sorptive capacity. However, it remains unknown to what extent the molecular weight of DOM mediates its dynamics, for example, influencing its role in DOM-microbe interactions and the processes determining the compositional assembly of DOM. To address this issue, ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and high-throughput sequencing were applied to investigate how the molecular weight of DOM was associated with its dynamics in two typical agricultural soils with different fertility. Our results showed that low-molecular-weight DOM had lower biological stability and a higher transformation potential. Analysis of the DOM-microbe co-occurrence network showed that low-molecular-weight DOM displayed tighter interactions with a diversity of microbes, while high-molecular-weight DOM interacted with only a few microbes. Ecological null models revealed that the compositional assembly of low-molecular-weight DOM, but not high-molecular-weight DOM, was more controlled by deterministic processes. Taken together, our results demonstrate the fundamental role the molecular weight of DOM plays in determining biological stability, transformation potential, interactions with microbes, and assembly mechanisms of DOM in agricultural soils. This work provides the foundation for general principles explaining complex dynamics of DOM in natural ecosystems, highlighting that using theories and concepts in metacommunity ecology, such as community diversity and assembly mechanisms, may open a new avenue to understand DOM dynamics from a macro perspective.

Soil microbial biomass is assumed to have stable chemical composition. Various components of the biomass such as DNA, ATP, or chloroform-labile organic carbon are measured in soil and converted into total microbial biomass using experimentally derived conversion factors, which are also assumed to be constant. However, several observations suggest the opposite. The composition of soil microbial biomass is likely changing with specific growth rate as observed in pure cultures of single microbial species. In this study, we define a “sub-Microbial” model that explicitly represents changes in composition of soil microbial biomass associated with changes in specific growth rate. We calibrate the model with published data and compare its performance with the simpler Monod and Pirt models, which consider microbial biomass as a single pool with invariant chemical composition. The model explains well the variability in chloroform-labile content of microbial biomass following organic substrate additions as well as variability in ratios of different components of microbial biomass. Changes in composition of soil microbial biomass are quantitatively significant and occur over hours and days resulting in our sub-Microbial model outperforming both the Monod and Pirt models. Our results further indicate that the composition of soil microbial biomass changes consistently with growth rate across various soils. Here, we provide a methodological recommendation how to determine total soil microbial biomass and its physiological characteristics such as growth rate, turnover rate and substrate use efficiency as accurately as possible. In light of the presented results, we would like to initiate a discussion about the methodological issues associated with measurement of soil microbial biomass as these measurements are expected to inform a new generation of microbially-explicit soil biogeochemical models predicting development of terrestrial ecosystems under various scenarios.

Soil microbes perceive drying and rewetting (DRW) events as more or less harsh depending on the previous soil moisture history. If a DRW event is not perceived as harsh, microbial growth recovers rapidly after rewetting (referred to as ‘type 1’ response), while a harsh DRW will be followed by a delayed growth recovery (‘type 2’ response). Predicting these responses based on pedoclimatic factors is important because they can determine how carbon is partitioned between growth (soil C stabilization) and respiration (C loss to the atmosphere). To characterize the microbially perceived harshness between the two extreme types 1 and 2, and its pedoclimatic drivers, we described microbial growth with a single logistic function and respiration with a rescaled gamma distribution using ∼100 growth and respiration datasets. These functions captured microbial growth and respiration rates well during the recovery phase after rewetting. Therefore, the fitted parameters from these functions could help us to capture the continuum of microbial recovery between type 1 and 2 and characterize harshness levels. The product of growth parameters τ (delay time) and b (the slope of the growth curve at time τ) was an effective index that could capture and quantify perceived harshness because it allowed separating type 1 and 2 responses better than τ or b alone or than any other parameter describing the growth or respiration response. The drier the soil before rewetting and the lower the pH, the higher was the perceived harshness (τ×b), the longer the delay of growth recovery, and the larger the CO2 loss at rewetting. Overall, this study places soil microbial responses to DRW along a continuous gradient from fast to slow recovery, where the faster the recovery, the better adapted the microbial community is to the DRW event.

Atmospheric methane (CH4) concentration has been increasing recently, contributing to global warming. As natural sinks, forest soils are expected to mitigate the atmospheric CH4 rise. However, it had been difficult to measure soil CH4 flux continuously and accurately because of the limited stability and precision of CH4 analyzers in the field. In this study, we measured hourly CH4 flux with plant roots (Root) and without roots (Trench) during the growing season in a regenerating deciduous forest using an automated chamber system with an up-to-date analyzer. Combined with a Random Forest (RF) approach, we studied the spatiotemporal variation and control of soil CH4 uptake rates. The results showed that the soil was a CH4 sink throughout the experimental period, and the existence of roots significantly enhanced CH4 uptake, mainly through improving soil aeration. The CH4 uptake rate varied seasonally according to the variations in soil gaseous diffusion caused by soil moisture and temperature differences. In addition, soil CH4 uptake showed a significant spatial variation, mainly resulting from spatial difference in soil porosity, soil carbon and nitrogen contents, and fine root biomass. The RF models showed high performance in soil CH4 flux prediction using the soil O2 diffusion coefficient and soil temperature as explanatory variables. The performance of RF models using ordinary variables of soil water content or water-filled pore space (WFPS) was equal to or slightly better than that of models using the diffusion coefficient. The higher importance of ambient CH4 concentration in Trench chambers indicates an increase in soil CH4 uptake at higher CH4 concentrations, which is predicted in the future. Although there are limitations, we believe that a machine learning approach, such as RF, using a large amount of continuous data with high temporal resolution, has great potential for investigating the dynamic variation in soil CH4 flux.

Soil multifunctionality is the consequence of biotic interactions that drive decomposition, nutrient cycling and net primary production. Energy flux describes the energy consumed and transferred among multitrophic groups in the soil food web, which are logically linked to multifunctionality. In a subtropical agroecosystem with an annual sweet potato-oilseed rape rotation, we explored how biochar and synthetic fertilizer jointly affected agroecosystem multifunctionality (e.g., crop production, soil carbon storage and nutrient cycling) and the energetic structure of the nematode food web during two consecutive years. Results showed that biochar increased soil multifunctionality by 37–110% mainly by promoting a uniform energy flow through the soil nematode food web, which was largely due to increased energy fluxes of fungivores and omnivores-carnivores at the expense of decreased energy flux through herbivores. Applying a lower rate of synthetic fertilizer led to non-uniform energy flow in the soil nematode food web, suggesting that nitrogen limitation could offset the stimulatory effect of biochar on soil multifunctionality. This was because biochar induced oligotrophic conditions (a stoichiometry-induced nitrogen limitation), effectively warranting that continuous biochar application would aggravate nutrient limitations to crops, especially when low rates of synthetic fertilizer are applied. Notably, soil nutrient impoverishment could lead to resource reallocation from aboveground shoot to belowground root production, thereby fueling the energy flow through the herbivore channel. Our findings highlight the importance of balancing biochar and synthetic fertilizer applications to sustain a stable energetic structure in soil nematode food webs, which are associated with greater crop production and soil health in subtropical region.

Managing and increasing organic matter in soil requires greater understanding of the mechanisms driving its persistence through resistance to microbial decomposition. Conflicting evidence exists for whether persistent soil organic matter (SOM) is molecularly complex and diverse. As such, this study used a novel application of graph networks with pyrolysis-gas chromatography-mass spectrometry to quantify the complexity and diversity of persistent SOM, defined as SOM that persists through time (soil radiocarbon age) and soil depth. We analyzed soils from the Cooloola giant podzol chronosequence across a large gradient of soil depths (0–15 m) and SOM radiocarbon ages (modern to 19,000 years BP). We found that the most persistent SOM on this gradient was highly aromatic and had the lowest molecular complexity and diversity. By contrast, fresh surface SOM had higher molecular complexity and diversity, with high contributions of plant-derived lignins and polysaccharides. These findings indicate that persisting SOM declines in molecular complexity and diversity over geological timescales and soil depths, with aromatic SOM compounds persisting longer with mineral association.

Soil microorganisms are a fundamental component of ecosystems and mediate biogeochemical cycles and ecosystem productivity. The frequency and extremity of fire weather is expected to increase under global warming; however, postfire soil microorganisms' patterns and trends remain unclear. By performing a global meta-analysis of 1019 paired observations of burned and unburned sites from 123 publications, we show that fungal biomass, microbial biomass carbon (C), soil respiration, autotrophic respiration, and C acquisition enzymes decrease in response to fire. The recovery times of microbial biomass and functional groups were shorter than those of soil C emissions and extracellular enzymes. Importantly, the postfire recovery of microbial biomass C and/or N as well as soil respiration and its components varied with mean annual temperature and precipitation, fire severity and type, and ecosystem type, with longer recovery times under high-severity fire/wildfire and in forests. Our study highlights the differential recovery patterns of microbial attributes after fire across global terrestrial ecosystems and reveals the importance of climate and the fire regime in regulating the postfire recovery of the soil microbial community and functioning.

Sulfur (S) availability plays key roles in the growth and health of microbes and plants, but little is known about how land use change and phosphorus (P) addition affect the soil S cycle. Based on a 10-year field nitrogen (N) and P addition experiment in three tropical forests (a primary forest, a rehabilitated forest and a disturbed forest), this study investigated the effects of land cover change, N addition and P addition on soil enzymes involved in carbon (C), N, P and S cycles. Results showed that the two secondary forests had lower S availability and higher microbial investments in arylsulfatase than the primary forest, indicating S deficiency in the two secondary forests. Correlation and path analysis showed that forest succession theory could explain the changes of absolute arylsulfatase activity while resource allocation theory explained the changes of specific arylsulfatase activity across the primary and secondary forests. Phosphorus addition had larger effects on soil properties and microbial biomass and activity compared to N addition. Phosphorus and NP addition significantly decreased extractable S by 27%∼43% in the three forests, resulting in increased absolute arylsulfatase activity (51%∼90%) and specific arylsulfatase activity (28%∼57%) in the primary and disturbed forests, but had little effect on absolute and specific arylsulfatase activity in the rehabilitated forest. Moreover, P and NP addition increased enzymatic stoichiometry of arylsulfatase to C and N-acquiring enzymes in the primary and disturbed forests, while tended to decrease ratios of arylsulfatase to C and N-acquiring enzymes in the rehabilitated forest. These results indicate that P fertilization with and without N addition can decrease soil S availability and induce S shortage for microbes. Results from this study advocate that we need to pay attention to S availability beyond N and P under the background of the decrease in atmospheric S deposition.

Earthworms are important soil organisms that play critical roles in ecosystem material cycling and energy flows. Discovering and predicting the distribution of earthworm habitats is critical for managing biodiversity conservation projects and improving ecosystem health. However, earthworm data are challenging to obtain, and studies on the distribution of earthworms and factors affecting this have mainly been conducted in fields at a small scale; the spatial distribution of earthworms throughout China remains unclear. Species distribution models have been effectively used in macro-scale species suitability distribution studies; however, they have certain limitations. Thus, here, we optimized the maximum entropy model (MaxEnt) to achieve low complexity and high transferability, and the model was capable of predicting the potential distribution of earthworms in China. Modeling was based on the use of a developed database containing 286 earthworm occurrence records and 31 environmental variables (19 climatic, 9 soil, and 3 topographic variables). Results show that earthworm distribution is mainly controlled by the following environmental variables (with corresponding contribution rates): minimum temperature of the coldest month (18.47%), digital elevation model (17.65%), coarse fragments (16.72%), soil organic carbon (9.65%), soil type (7.53%), mean diurnal range (5.35%), and soil thickness (5.05%). The variables with the strongest influence on distribution are climate followed by landforms and soils. The relationship between the effect of environmental variables and earthworm distribution is not simple and linear, and each element has a certain threshold range. Only 50.67% of the total land area of China provides a suitable habitat for earthworms, and there are remarkable spatial differences. Of the various ecosystems, woodland ecosystems provide most of the suitable habitats, followed by cropland and grassland ecosystems, which together account for 45.74% of the land area. This study can be used as a reference for understanding and assessing ecosystem health, sustainability, and for enabling biodiversity conservation.

Meadows and forests are the main vegetation types in temperate terrestrial ecosystems, and largely contribute to soil carbon (C) stock. Bioavailable C inputs can accelerate microbial decomposition of soil organic matter (SOM), which is known as “priming effect”. However, it is still unclear how priming effect, as an important mechanism influencing soil C sequestration, is influenced by spatial transition of vegetation from meadow to forest. To investigate the mechanism of priming effect along a spatial transition gradient of vegetation, a soil incubation experiment with 14C labeled glucose was combined with microbial rDNA sequencing and gene composition prediction. The results showed that with the vegetation transition from meadow to forest soil available phosphorus (P) significantly increased, in contrast to dissolved nitrogen (N) and C which remained unaffected. Moreover, the soil microbial community composition shifted towards a higher relative abundance of K-strategists (Acidobacteria) and a lower abundance of r-strategists (Actinobacteriota) along the vegetation transition from meadow to forest.In the meadow, the microbial community consumed more of the added glucose and increased priming effect. This was accompanied by lower available P but higher soil bacterial gene function encoding P cycling. In contrast, increased soil P availability in forest soils caused a decelerated microbial metabolism of phosphorylated organic compounds within microbial biomass due to decreased microbial demand for P acquisition from SOM, and thus resulted in suppression of the priming effect. Our study showed that P availability and microbial community shifts in spatial transition zones between meadows and forests are important drivers for the priming effect on SOM decomposition.

Chemotaxis is a process that enables motile bacteria to move along nutrient gradients, thereby exploring nutrient hotspots, and potentially playing important biogeochemical roles in agricultural ecosystems. In this study, a 36-year field experiment of nitrogen (N) input was conducted, along with the use of a synthetic community (SynCom) inoculation, to confirm the role of chemotaxis in the cycling of N. The chemotaxis genes abundances of N+ treatments were 97.2% and 95.3% higher than that of N- treatments in bulk soil and rhizosphere, respectively, indicating a significant increase in chemotaxis genes under long-term N input. Positive correlations between chemotaxis genes and N metabolism genes in N+ treatments suggested an important role of chemotaxis in N cycling. The chemotaxis genes abundance was 3.6 times higher in rhizosphere than in bulk soil, and chemotaxis genes showed the most complex correlations with N metabolism genes in rhizosphere under N input, suggesting a key role of chemotaxis in plant N uptake. To assess the potential function of chemotactic bacteria, a SynCom consisting of 10 bacterial strains isolated from in situ N-input soils and capable of chemotaxis, was applied to the maize rhizosphere. The promotion of N acquisition in maize plants through inoculation was confirmed by about 30% greater N content in the shoots of SynCom inoculated soil than in the control. Long-term N input enhanced the functions related to metabolite transport and energy metabolism in the bacterial community, particularly in the rhizosphere. Thus, plants may provide bacteria that migrate to the rhizosphere via chemotaxis with more root metabolites as nutrients. In summary, this study provides novel ecological and molecular insights into chemotaxis-mediated biogeochemical cycling in agricultural ecosystems.

Over the last few years, several researchers working on the development of “biogeochemical” or “ecosystem-scale” models of soil carbon dynamics have reported struggling with a number of difficult challenges. At the same time, work in this area has focused exclusively on microbial activity described at a macro-ecological level, and has entirely bypassed the abundant literature produced in the last two decades on the study of soil processes at the microscale. Juxtaposition of these different observations suggests that a radical shift of perspective is in order. In this general context, the present article carries out an in-depth analysis of several of the key limitations of current ecosystem-scale models and recommends a number of steps to shift the perspective to one that is argued to have a better chance of success in the relatively short time we have to address several pressing soil-related environmental problems. These steps, in particular, require the development of large-spatial-scale models of soil carbon dynamics to be far more interdisciplinary than it has been till now, and to adopt a “bottom-up” approach, building on what the research at the microscale reveals about soil processes. Nevertheless, because it may assist in upscaling efforts, it is argued that some room should be preserved for work to continue on the search for empirical models applicable at large spatial scales.

The introduction of novel perennial grains into annual row crop rotations is proposed to increase soil ecosystem services and enhance plant-soil-microbial linkages because perennials provide deeper root systems and more continuous ground cover than annuals. While soil microbial communities underpin many ecosystem services, we know little about how soil microbial composition and diversity, and soil carbon storage, differ between soils of annual vs. perennial grain crops. We measured soil fungi: bacteria (F/B) ratios and soil carbon within the novel perennial intermediate wheatgrass (IWG; trademarked Kernza®) and tilled annual wheat and compared soil microbial diversity and community composition within their rhizosphere, shallow bulk soil (0–15 cm) and total bulk soil (0–90 cm). After three years, soil depth explained 30–40% and 12–22% of the variance in bacterial and fungal community composition, respectively, while crop type explained 10% and 9–16% of the variance, respectively. Fungal communities were most impacted by crop type in the rhizosphere and shallow bulk soil and less sensitive to differences in soil depth. In contrast, crop type had a smaller effect on bacterial communities which were more influenced by soil depth. IWG trended higher in soil carbon mass at 0–30 cm (p = 0.22) and had a higher (F/B) ratio than tilled annual wheat at depths below 15 cm, but tilled annual wheat had higher soil carbon concentration (p = 0.12) and soil carbon mass (p = 0.09) at the 60–90 cm soil depth. Our results indicate that fungi were more responsive than bacterial communities to crop type and that IWG has a higher fungal biomass and different fungal community composition than annual wheat at depth. However, despite these distinct differences in fungal communities in IWG compared to annual wheat, the differences did not translate into greater soil carbon mass in IWG at depth.

Chitin is an insoluble and ubiquitous soil biopolymer, estimated to be the second most abundant organic soil biopolymer on Earth. Despite its abundance, role as a source of C and N in soil, and importance to ecosystem function, further research is required to elucidate key controls on chitin breakdown under varying environmental conditions. Previous work highlights the important role rhizosphere microbiomes and root exudates can play in chitin catabolism. To enable mapping of chitinase activity within the highly heterogeneous and spatially organized rhizosphere, we designed and synthesized an enzymatically activated fluorogenic substrate, chitotriose-TokyoGreen (chitotriose-TG), by incorporating a fluorescein derivative (TG) onto the trimeric unit of chitin. This non-fluorescent substrate is selectively hydrolyzed by chitinase to release TG and yield a fluorescence signal, which can be used to spatially image and measure chitinase activity in the rhizosphere. To demonstrate the application of this technique, we grew switchgrass (Panicum virgatum) in rhizoboxes amended with a horizontal layer supplemented with chitin. We extracted mobile proteins from the rhizobox using a nitrocellulose membrane blotting technique which offers non-destructive enzyme extraction while preserving the 2D spatial position of the enzymes. We then subjected these membranes to the synthesized chitotriose-TG stain to spatially visualize the distribution of chitinase activity within the rhizosphere. We observed increased chitinase activity near switchgrass roots and higher activity within the soil zone enriched in chitin, showing an adaptive response of chitinase production with spatial focusing in areas of higher chitin abundance. Thus, the enzyme extraction and visualization strategy we describe here can enhance efforts to better understand spatial controls on chitin breakdown in rhizosphere, further elucidating the role of chitin as a C and N source in these systems.

Forest ecosystems are considered globally important sinks for offsetting increasing anthropogenic atmospheric carbon dioxide (CO2), however, this may be limited by the soil nutrient supply, predominantly nitrogen and phosphorus. Uncertainty remains regarding how soil N cycling in mature forests may respond to changes in carbon availability, arising from enhanced photosynthesis under elevated CO2 (eCO2) due to lack of experimental data. Further, potential positive feedbacks of nitrous oxide emissions may offset benefits of additional carbon sequestration under eCO2. The Birmingham Institute of Forest Research Free Air Carbon Enrichment experiment (BIFoR-FACE) started fumigating a mature temperate deciduous forest in 2017 at +150 ppm CO2 above ambient. Soil N cycling responses to eCO2 were investigated using the 15N pool dilution approaches to assess gross N mineralisation, immobilisation and nitrification rates, in combination with the 15N-gas flux method to quantify and source partition N2O production from 2018 to 2020 (2nd to 4th year of fumigation). Soil gross N mineralisation increased by 20% under eCO2 (6.6 μg N g−1 d−1) compared to the control treatment (5.3 μg N g−1 d−1) and despite the trends being consistent over the three years (2018–2020), the high variability between arrays reduced statistical significance except in 2019. Ammonium immobilisation by microbes increased by 20% under eCO2 (3.5 μg N g−1 d−1) as well. Overall, gross mineralisation was 4 times higher than nitrification, indicating a much higher ammonium turnover rate compared to nitrate (1.5 vs. 12 days mean residence time). N2O emission from denitrification (0.18 ng N g−1 h−1) was significantly higher under eCO2. After four years of CO2 fumigation, there are modest indications of enhanced soil N transformation rates and N availability to support the observed enhanced canopy CO2 uptake. Increased N2O fluxes under eCO2 indicated the potential for positive feedbacks on C sequestration under rising atmospheric CO2. The overall implications for C sequestration will depend on how long upregulation of soil N transformations and N bioavailability will last to meet plant demands before manifestation of N limitation, if any.

Although dead fungal mycelium (necromass) represents a key component of biogeochemical cycling in all terrestrial ecosystems, how different ecological factors interact to control necromass decomposition rates remains poorly understood. This study assessed how edaphic parameters, plant traits, and soil microbial community structure predicted the mass loss rates of different fungal necromasses within experimental monocultures of 12 tree species in Minnesota, USA. Necromass decay rates were most strongly driven by initial chemical composition, being significantly slower for fungal necromass with higher initial melanin content. Of the extrinsic ecological factors measured, variation in the amount of mass remaining for both low and high melanin necromass types was significantly predicted by soil bacterial richness and fungal community composition, but not by any soil microclimatic parameters or plant traits. Further, the microbial communities governing decay rates varied depending on the initial necromass chemical composition, suggesting that extrinsic and intrinsic factors interacted to propel decomposition. Finally, we also found significant positive relationships between the amount of remaining fungal necromass and soil carbon and nitrogen concentrations. Collectively, these results suggest that, after the initial chemical composition of dead fungal residues, soil microbial communities represent the main drivers of soil necromass degradation, with potentially large consequences for soil carbon sequestration and nutrient availability.

It has been proposed that competition between ectomycorrhizal (ECM) fungi and free-living saprotrophs for resources like nitrogen (N) slows decomposition and increases the soil carbon storage in ECM ecosystems compared to arbuscular (AM) ecosystems. However, empirical evidence for the generality of such ECM effects is equivocal, and confounding mechanisms have been proposed that affect the magnitude and direction of ECM effects on soil carbon. Here we conduct a theoretical modeling experiment, where we explicitly incorporate mycorrhizal processes into the Carbon, Organisms, Rhizosphere, and Protection in the Soil Environment (CORPSE) model. We use the model to explore the conditions under which ECM N acquisition processes can induce stronger saprotrophic N limitation and result in slower decomposition rates and greater soil organic carbon accumulation compared to AM processes. We found that the ECM fungi more strongly inhibited decomposition when litter inputs were N-depleted and relatively recalcitrant and when ECM fungi possessed a strong capacity to mine N from both recalcitrant soil organic matter and microbial necromass. Climate and seasonality also played a role as the ECM competition effect was strongest at low mean annual temperatures and when litterfall peaked seasonally. Priming effects driven by high root exudation rates in ECM-dominated systems could overwhelm the competition effect and reduce soil carbon under some circumstances. The ECM effect on decomposition in our simulations was highly context dependent. Based on our model results, we expect to see a strong ECM competition effect in temperate deciduous and boreal forests with relatively recalcitrant litter inputs, and with ECM fungi that produce oxidases and necromass-degrading enzymes. However, even a relatively strong ECM competition effect on decomposition only increased soil organic carbon accumulation by ∼10%.

Unraveling the mechanistic controls of methane (CH4) cycling in northern peatland ecosystems is crucial for understanding peatland-climate feedbacks. Growing evidence indicates that the microbial reduction of organic matter as a terminal electron acceptor can be a key regulator of CH4 production in peatlands, but the role of microbial organic matter reduction in different peatlands has not been well explored. Using an electron shuttling capacity assay, we investigated the relationship between the microbial reduction of organic matter and anaerobic CH4 and carbon dioxide (CO2) production in peatland soils in three experiments. In the first experiment, we surveyed the importance of microbial organic matter reduction in six soils representing the ombrotrophic-minerotrophic peatland gradient. In the second experiment, we further explored the reduction of solid-phase organic electron acceptors in a minerotrophic fen and compared these results to previously published values from an ombrotrophic bog (the end members of the initial gradient surveyed). Results from these experiments suggest that microbial organic matter reduction suppresses CH4 production, especially in ombrotrophic peat soils, likely helping to explain low CH4 production in bog-like soils. In contrast, the pool of oxidized organic matter was quickly reduced in minerotrophic peat soils which subsequently exhibited higher rates of CH4 production. In the final experiment, we investigated the effect of temperature on microbial organic matter reduction in the same ombrotrophic bog soil, demonstrating that warmer temperatures resulted in both a faster reduction of solid-phase organic matter and an apparent increase in the size of the organic electron acceptor pool that can be reduced by microbes. Future work should explore the drivers of the observed differences in microbial organic matter reduction in different peatland soils to provide a stronger mechanistic explanation for how this process will regulate peatland greenhouse gas dynamics in the face of global change, including increases in temperature.

Global climate warming is propelling an increase in forest wildfires and relevant ecosystem degradation. How the legacy effect of wildfires will act on soil multifunctions and whether litterfall, especially prominent in terms of biotically induced functions, will contribute most to the recovery patterns after wildfires remain largely unexplored. To fill these gaps in knowledge, comprehensive soil function assessments were conducted using 38 soil indicators, covering five functional groups, namely, soil buffering and filtration, water conservation, carbon storage, nutrient cycling and microbial habitat. We tracked their shifts and the overall soil multifunctionality in paired burned and unburned sites during the mid-growing season from 2019 to 2021 (i.e., the first three years following high-severity wildfires) over the Pinus tabuliformis plantation of North China. The responses of the trade-offs and synergies between soil functions to wildfires, year and their interaction were illuminated. We further determined 18 biotic (i.e., understory plant and litterfall) and abiotic (i.e., soil temperature) variables to explain the mechanism of variations in soil multifunction. Results showed that soil multifunctionality and most single functions of the burned site were coherently less than those of the unburned site, whereas the opposite pattern was found for the soil microbial habitat, which is particularly significant in the first post-wildfire growing season. Although mutual benefit and win–win results were the melody of soil multifunction, trade-offs/synergies among functions in the burned site were dampened over time. Plant attributions explained 60.6% of the variation in soil water conservation, whereas they and litterfall properties played as the main direct pathways to wildfire impacts on soil buffering and filtration. We highlighted the tremendous effect of litterfall mass on soil multifunctionality as well as carbon storage and nutrient cycling independent function, largely overpassing those of plant attributions and soil temperature. These findings unfold the potential of litterfall input as a suitable early intervention for facilitating soil functioning after wildfires. Moreover, the strong interactions of wildfires and time shed lights on the requirement for long-term frameworks concurrently considering biotic and abiotic factors to understand the overall situation of wildfire influences on ecological processes.

Both herbivorous and bacterivorous microfauna have been shown to influence root development, soil nitrogen (N) mineralization, and plant productivity. However, our knowledge of these effects is limited as multitrophic interactions remain largely unexplored. We investigated whether and how herbivorous nematodes (Pratylenchus zeae) and bacterivorous nematodes (Poikilolaimus oxycercus), alone and in combination, affect plant biomass (Lolium multiflorum) through root traits and/or soil N mineralization. Bacterivorous nematodes increased, whereas herbivorous nematodes decreased, plant productivity. We found that root trait coordination in response to soil microfauna was consistent with the concept of root economics space. The negative interaction between herbivorous and bacterivorous nematodes on plant productivity at high herbivorous nematode infestation could be explained by reduced N mineralization and variation in the root nitrogen concentration-root tissue density (RNC-RTD) axis aligned with increased herbivory intensity. This study revealed that herbivorous and bacterivorous nematodes moderated each other's effect on plant productivity via root trait coordination and N mineralization, and suggests, for the first time, the value of the root economics space concept for interpreting phenotypic root plasticity and functioning in response to local biotic factors.