Soil Heterogeneity Research Articles

Consequences of plateau pika disturbance on plant-soil carbon and nitrogen in alpine meadows.

The presence of burrowing mammals can have extensive effects on plants and soils, creating bare soil patches in alpine meadows and potentially altering plant-soil carbon (C) and nitrogen (N). This study focuses on the plateau pika (Ochotona curzoniae) to examine the responses of plant-soil C and N to a small burrowing mammal from quadrat scale to plot scale. The density of active burrow entrances in disturbed plots was used as an indicator of the disturbance intensity of plateau pikas. The study found that the below-ground biomass (BGB) and its C and N, as well as soil C and N concentrations were significantly lower in bare soil areas than in vegetated areas and undisturbed plots. This shows that the quadrat scale limited the estimation of the C and N sequestration potential. Therefore, further research on the plot scale found that the disturbance by plateau pika significantly reduced plant biomass and BGB carbon stock. However, plateau pika did not affect soil C and N stocks or ecosystem C and N stocks. These findings suggest the bare soil patches formed by plateau pika caused plant and soil heterogeneity but had a trade-off effect on plant-soil C and N stocks at the plot scale. Nevertheless, moderate disturbance intensity increased the C and N sequestration potential in grassland ecosystems. These results provide a possible way to estimate how disturbance by small burrowing mammals affects C and N cycling in grassland ecosystems while accurately assessing the effects of small burrowing mammal densities on C and N in grassland ecosystems.

Adaptive Utilization of Pressure Sensor Data in Excavation

Abstract The assessment of soil parameters in construction holds significant importance for refining building information modeling (BIM). Our study aimed to investigate the adaptive utilization of pressure sensor data as a dynamic and computationally efficient tool for this purpose. The results reveal a significant correlation between the pressure sensor readings of the hydraulic cylinder in the excavator bucket and the total load during static-dynamic penetration tests conducted in both homogeneous and heterogeneous soil. This correlation holds true across a 100% range of torque, with values recorded at 0.60 and 0.93, respectively. A key strength of this methodology lies in that it enables near real-time detection of verified boundary levels. This feature streamlines the adoption and development of BIM-based excavation methods that seamlessly align with current practical conditions. Keywords: Soil boundary, detection, hydraulic pressure, static-dynamic penetration test, correlation, model-based design, ground investigation.

Drivers distinguishing of PAHs heterogeneity in surface soil of China using deep learning coupled with geo-statistical approach

Although numerous studies have reported the influencing factors of polycyclic aromatic hydrocarbons (PAHs) in surface soil from source, process or soil perspectives, the mechanism of PAHs heterogeneity in surface soil are still not well understood. In this study, the effects of 16 PAHs in surface soil of China sampled between 2003 and 2020 with their 17 “source-process-sink” factors at 1 km resolution (N = 660)) were explored using deep learning (eXtreme Gradient Boosting) to mine key information from complex dataset under the optimized parameters (i.e., learning rate = 0.05, maximum depth = 5, sub-sample = 0.8). It was observed that top five factors of 16 PAH had the largest cumulative contribution (i.e., from 84.8% to 98.1%) on their soil concentrations. PAH emission was the predominant driver, and its effect on soil PAH increases with increasing logKow. Soil was the second driver, in which clay can promote the partition of PAHs with low or middle logKow. However, sand can accumulate those congeners with high logKow. Moreover, the deep learning plus geo-statistical models (with low deviation for testing dataset (N = 283)) were capable of predicting soil PAH concentrations using their drivers with high accuracy. This study improved the understanding of the environmental fate and spatial variability of soil PAHs, as well as provided a novel technique (i.e., deep learning coupled with geo-statistics) for accurate prediction of soil pollutants.

Effects of soil heterogeneity and preferential flow on the water flow and isotope transport in an experimental hillslope

Soil water movement plays vital roles in hillslope runoff generation and groundwater and surface water interaction. However, there are still knowledge gaps about the impacts of soil heterogeneity and preferential flow on the internal water flow and transport process. In this study, the vertical soil heterogeneity focused on the variations in soil retention capacity, and the consideration of lateral preferential flow emphasized the higher hydraulic conductivity. We combined isotopic tracing and numerical modeling in an artificial hillslope, focusing on monitored processes of the artificial rainfall and isotopic tracing experiment. The results showed that the soil moisture quickly accumulated at the bottom of the hillslope during rainfall events, while the 2H enrichment occurred in the topsoil derived from enriched isotope injection in the second artificial rainfall. The evaporation process slowed down the mixing of new water in the topsoil and old water in the lower layer. We found that the vertical soil heterogeneity had significant influences on the internal water and isotope transport paths within the hillslope. The lateral preferential flow played an important role in the water flux and transport time to the seepage face. The coupling of isotopic tracing, which reflects the water transport and mixing with the hillslope, effectively improved the model simulation and mechanism analysis of hillslope water flow. Our findings provide new insights into the mechanisms governing soil water flow and transport dynamics in hillslopes, taking into account vertical soil heterogeneity and lateral preferential flow.

Thermal conductivity in a vadose zone: A novel spectral solution and application by the implication of significant coherence of thermal condition in the shallow soil water layer

AbstractIn the context of the heterogeneity in the unsaturated or vadose zone, accurately representing the analytical mechanisms and in‐situ water content within the soil layer poses a significant challenge. Particularly in shallow layers, thermal conditions exhibit rapid changes in response to evolving surface temperatures. This study proposes a hypothesis suggesting that the in situ heat mechanism may notably impact the soil water layer. The research introduces an innovative approach to theoretically uncover thermal conditions, including soil temperature, soil temperature gradients, and heat flux, within the shallow Quaternary gravel layer at various depths through spectral analysis of temporal observations. The study presents a stochastic inverse solution to estimate thermal conductivity by leveraging spectral analysis of soil heat flux and temperature gradients. The findings reveal that thermal conditions exhibit the most prominent periodic fluctuations during the diurnal process over a 24‐hour cycle. The soil temperature gradients and heat flux measurements at depths of 0.1, 0.3, 0.6, and 1.2 m demonstrate their ability to capture changes in soil temperature and air temperature to a certain extent within the frequency domain. Furthermore, the analysis highlights the intrinsic uncertainty and sensitivity of estimating thermal conductivity in heterogeneous soil environments. The wide variability observed in thermal conductivity values, coupled with their dependence on soil type and environmental conditions, underscores the need for careful consideration of these factors in future studies and modeling efforts. Applying the derived inverse spectral solution allows for determining thermal conductivity throughout the soil‐water system across depths ranging from 0.1 to 1.2 m. As a result, this research demonstrates the feasibility and practicality of assessing the thermal conductivity of the soil layer in conjunction with heat flux and temperature gradients through spectral analysis.

Spatial infiltration and redistribution of light crude oil in heterogeneous water-bearing soil layers under different hydrogeological processes.

Two physical models were used to simulate the infiltration and redistribution process of light crude oil after leakage in a heterogeneous soil layer following water level variation and rainfall. Migration fronts and redistribution characteristics of oil during gravity seepage, water level variation, and rainfall were obtained using charge-coupled device (CCD) camera shooting and cyan-magenta-yellow‒black (CMYK)-based gray analysis, which were employed efficiently and at a low cost. Then, the influencing factors and migration mechanisms were examined. Finally, the soil water and oil contents were measured to verify the simulation results. The results are as follows: (1) the geologic lens and fine-coarse interface can intercept oil, resulting in a local highly contaminated area. (2) The crude oil infiltration path and velocity varied greatly with the different soil types and initial water contents. Within a certain range, the higher the initial water content is, the higher the lateral and vertical infiltration speeds. (3) The oil redistribution process was dominated by vertical infiltration under the condition of water level variation or rainfall, but oil-water displacement and the capillary pressure caused some oil to move horizontally near the geologic lens and fine-coarse interface. (4) Water level variation resulted in a synchronous rise or fall of the oil accumulation area, but rainfall caused it to move up. (5) Water level variation and rainfall imposed a certain influence on the periodic accumulation and release of crude oil in heterogeneous soil, especially in the presence of geologic lenses and lithologic interfaces.

Comparison of distinctive diversities, co-occurrence patterns and potential ecological functions of microbial communities in heterogeneous soil areas in typical subtropical forests, southeast China

Although microbes are crucial in ecological cycling in forest soil, the response of the network structure and ecological functions of these microorganisms to soil heterogeneity remains elusive. Here, we analyzed the composition and co-occurrence network patterns of microorganisms in heterogeneous soil areas and evaluated their potential ecological functions, taking the scenic area (SA) and nature reserve (NR) of Wuyishan National Park as examples. Our results showed that the soil properties of SA and NR could almost be clustered separately, and soil heterogeneity between them has been found. Prokaryotic communities in both areas were also divided and showed higher similarities individually than those of eukaryotes. The prokaryotic community composition in both areas was mainly affected by pH and ammonia, while the eukaryotic community composition was mainly affected by total carbon and the carbon to nitrogen ratio. Both the microbial network and ecological function network in SA were more complex than those of NR, while those of NR were more stable than those of SA. The keystone taxa of pro- and eukaryotes with important ecological functions were enriched in SA and NR, respectively. Moreover, significant discrepancies between SA and NR were found in the prokaryotic functions related to nitrogen cycling, sulfur cycling, and compound degradation. Our study illuminated that the soil heterogeneity in subtropical areas changed microbial community diversity, interaction patterns, and keystone taxa composition, and might further affect their ecological functions.

The effect of soil texture, layering and water head on the infiltration rate and infiltration model accuracy

AbstractInfiltration is one of the most important physical characteristics of soil and depends on various factors. This study investigated the influence of soil texture, layering and water head on the soil water infiltration rate. It also selected the most accurate infiltration models to determine the water infiltration rate in homogeneous and heterogeneous soil profiles. Experiments were carried out in four soil containers with a length, width and height of 20 × 20 × 70 cm. Treatments consisted of two soil textures (sandy loam, SL; clay loam, CL), four soil profiles (homogeneous texture, SL and CL; and heterogeneous texture, lighter texture on the top, SL/CL, and heavier texture on the top CL/SL) and three water head sizes (4, 7 and 10 cm). Several models were used to determine the water infiltration rate under homogeneous (Kostiakov, modified Kostiakov, Philip, Horton, traditional Green–Ampt, modified Green–Ampt and HYDRUS‐1D) and heterogeneous soils (traditional Green–Ampt, modified Green–Ampt and HYDRUS‐1D). According to the results, the infiltration rate decreased over time and along the soil profile. Nevertheless, it jumped at the interface of two‐layered soils when the heavier soil was in the bottom layer (SC treatments) due to the high potential of the second layer, and then it decreased. In the reverse layering, the infiltration rate in the interface was lowest (CS treatments) because of the higher hydraulic conductivity of the second layer. Additionally, the infiltration rate increased with increasing water head, but the rate of this increase was higher by changing the water head from 7 to 10 cm. The results of infiltration models showed that the accuracy of these models was higher in clay loam texture than in sandy loam texture. The modified Green–Ampt was the most accurate model in homogeneous and layered soils, with average RMSE of 0.0204 and 0.019, respectively. The Horton model had the weakest simulation in homogeneous soils, with an average RMSE of 0.1299. Additionally, the accuracy of HYDRUS‐1D in layered soils was less than that in homogeneous soils (NS of 0.95 and 0.85, respectively), and its accuracy decreased with increasing water head in most treatments.

Comparative assessment of the change in the species composition of vegetation on the territory of the western field of RSAU-MTAA

The article presents the analysis of changes in the floral composition of the western field of the Ecological Station of the Russian State Agrarian University – Moscow Timiryazev Agricultural Academy for 4 years. The research object is located in the center of the megalopolis, it is subject to high anthropogenic load, as it is surrounded on both sides by a road network, and at the same time it is part of the facies of the Forest Experimental Dacha. The site is characterized by close occurrence of groundwater, high density of upper soil horizons, heterogeneous soil structure and mesorelief, resulting of in flooding. As a result of a significant number of anthropogenic and abiotic factors, it is necessary to analyze the vegetation composition and the species richness of the area in order to assess the dynamics of variability of these conditions and to predict the potential stability of the biological diversity of the area. The changes in the species composition were analyzed by describing the vegetation and evaluating quantitative indicators: frequency of occurrence, abundance of species, degree of their dominance according to the O. Drude scale, as well as the Shannon index and indicators of species richness and saturation.The studies carried out showed a pronounced variability in vegetation cover from 2018 to 2022. During the study period, there was a change in plant families and an increase in species diversity: richness and saturation indices. In 2022, there was an increase in the number of species and an increase in the uniformity of their numbers compared to 2018.

Regulation of soil nitrogen cycling by shrubs in grasslands

Globally, grasslands are experiencing shrub expansion, but the effects of such plant community shifts on soil N cycling are seldom investigated. We explored the spatial heterogeneity of total soil N content by grid sampling down to a soil depth of 1.2 m, and analyzed net ammonification and nitrification rates in the top 0.2 m, during the growing season, in response to the patchiness of grasses and four shrub species in a grazed meadow on the Tibetan Plateau. The δ15N analyses of plant, soil, and mineral N (NH4+ and NO3−) revealed differences in N absorption strategies between shrubs and grasses. Heterogeneity in the total soil N distribution was common to at least a depth of 1.2 m. The lower δ15N values of the 1.2 m soil profile under shrubs were consistent with the lower δ15N values of leaves, aboveground litter, and roots of shrubs compared to grasses, reflecting the imprint of long-term N cycling in the soil as affected by shrubs. Increases in total soil N stock in the entire 1.2 m profile by 28%–32% under non-leguminous shrubs relative to grasses were ascribed to N accumulation in the lower 0.8 m. Consequently, deep sampling is essential for accurate estimation of soil N storage in shrubby meadows. The total N stock in soil under the leguminous shrub species was similar to that under grasses, which showed that the effect of shrubification on soil N storage depends on the shrub species. Nitrification rates in the topsoil under all shrubs were greater than under grasses, producing higher 15N-depleted NO3− contents under shrubs. Therefore, the lower δ15N signatures of shrub tissues compared to grasses reflected a preferential or adaptive uptake of NO3− by shrubs. The expansion of shrubs in grasslands creates high heterogeneity in N cycling and storage down to a considerable soil depth.

Intercropping of Pteris vittata and maize on multimetal contaminated soil can achieve remediation and safe agricultural production

Soil contamination by multimetals is widespread. Hyperaccumulator–crop intercropping has been confirmed to be an effective method for arsenic (As)- or cadmium (Cd)-contaminated soil that can achieve soil cleanup and agricultural production. However, the influencing factors and response of hyperaccumulator–crop intercropping to multimetal-contaminated soil are still unclear. In this study, intercropping of the As hyperaccumulator Pteris vittata and maize was conducted on two typical types of multimetal-contaminated soil, namely, Soil A contaminated by As, Cd, and lead (Pb) and Soil B contaminated by As, Cd, and chromium (Cr). Intercropping reduced As, Cd, and Pb in the maize grains by 60 %, 66.7 %, and 20.4 %, respectively. The concentrations of As, Cd, Pb, and Cr in P. vittata increased by 314 %, 300 %, 447.3 %, and 232.6 %, respectively, relative to their concentrations in the monoculture plants. Two soils with different levels of contamination showed that higher heavy metal content might diminish the ability of intercropping to reduce soil heavy metal risk. No notable difference in soil microbial diversity was found between the intercropped and monocultured plants. The composition of microbial communities of intercropping groups were more similar to those of monoculture P. vittata on two different soils (Soils A and B). An imbalance between the amount of As taken up by the plants and the reduction in As in the soil was observed, and this imbalance may be related to watering, As leaching, and heterogeneity of soil As distribution. Reducing the risk resulting from As leaching and enhancing the efficiency of phytoextraction should be emphasized in remediation practices.

Spatial soil heterogeneity rather than the invasion of Spartina alterniflora drives soil bacterial community assembly in an Eastern Chinese intertidal zone along an estuary coastline

The invasion of Spartina alterniflora (S. alterniflora) significantly influences the stability and transformation of soil organic carbon in coastal ecosystems. However, the impact of this invasion on the assembly of soil bacterial communities along estuary coastlines and soil profiles remains unclear. This study involved collecting soil samples from different environments (areas covered with S. alterniflora vs. barren flats) along the coastline of an estuary. The samples were taken at different depths (0–20 cm, 20–40 cm, 40–60 cm, 60–80 cm, 80–100 cm) within a 1-meter soil profile in the intertidal area of Xiaoyangkou Estuary in Jiangsu, China. The invasion of S. alterniflora had a notable impact on soil SOM (soil organic matter), DOC (dissolved organic carbon), POC (particulate organic carbon), and MAOC (mineral-associated organic carbon). Concurrently, the soil layer primarily influenced the levels of soil DOC and MAOC. The dominant bacterial communities inside the soil consisted of Proteobacteria (27.4–50.2 %), Bacteroidota (5.2–23.3 %), and Desulfobacterota (9.5–19.8 %), which participates in several elemental cycles, such as the carbon, nitrogen, sulfur, and phosphorus cycles. The changes in the patterns and functions of bacterial communities related to carbon cycling were mostly associated with the estuary shoreline, rather than being influenced by the invasion of S. alterniflora or variations in soil depths. Soil total carbon (TC) and SOM displayed a greater influence than other soil organic fractions on the distribution of the bacterial community. Furthermore, elements such as As, Cr, and Zn also exerted a significant impact on the assembly of soil bacterial communities. Our research findings suggest that the influence of S. alterniflora invasion on the composition and functioning of soil bacterial communities is contingent upon the specific features of the area. These characteristics, in turn, control the stability of soil carbon and the transformation of various types of soil carbon.

Theoretical substantiation of regular system of horizontal drains (a new approach)

The nonlinear problem of regulating the water-physical conditions of over-drained and over-wetted agricultural lands through a regular system of horizontal drains has been formulated and solved by analytical methods. The dynamics of groundwater reserves are analyzed in a generalized manner, rather than locally as done previously. A dependence has been derived to describe the behavior of the water table averaged over the interdrain space, considering a targeted change in head within the drains. Based on this, a formula has been obtained for calculating the optimal drain spacing in both homogeneous and heterogeneous soils, taking into account the requirements for their water-physical state. An assessment was conducted on the uneven distribution of groundwater caused by the local action of horizontal drains. Examples with typical initial data illustrate the decrease in the average water table over time and demonstrate the potential for rarefaction of reclamation drainage using a new methodological approach. This approach will significantly reduce capital costs for its construction and reconstruction.

Semi-analytical and numerical modeling of U-bend deep borehole heat exchanger

U-bend deep borehole heat exchanger (DBHE) is a new promising kind of ground heat exchanger, but nowadays there are lack of accurate efficient models to simulate U-bend DBHE. This paper has developed a semi-analytical model of U-bend DBHE, which considers the unsteady heat transfer of borehole, heterogenous soil thermal properties and geothermal gradient. A 2D numerical model and an analytical model based on infinite line-source theory are also developed, and the three models are compared with experimental data for different boundary conditions. Based on the soil thermal properties estimated by logging data and rock identification, the three models have large errors when compared with experimental data. Based on a soil thermal conductivity λs estimated by matching experimental data, the three models match better with experimental data, and it is inferred that λs should be measured by thermal response test instead of rock identification. The semi-analytical model and 2D numerical model match very well for all the time, but the analytical model has large differences with 2D numerical model, which is because the analytical model ignores borehole heat capacity and time-varying heat flows at the borehole wall. This paper could provide a cost-effective semi-analytical model and some advices for U-bend DBHE.

Differential Gene Expression Patterns in Peach Roots under Non-Uniform Soil Conditions in Response to Organic Matter.

Organic matter (OM) amendments are often encouraged in sustainable agriculture programs but can create heterogeneous soil environments when applied to perennial crops such as peaches (Prunus persica (L.) Batsch). To better understand the responses of peach roots to non-uniform soil conditions, transcriptomic analysis was performed in a split-root study using uniform soil (the same soil type for all roots) or non-uniform soil (different soil types for each half of the root system) from either (1) autoclaved sand (S), (2) autoclaved sand with autoclaved compost (A), or (3) autoclaved sand with compost which included inherent biological soil life (B). Each uniform soil type (S, A, and B) was grouped and compared by uniform and non-uniform soil comparisons for a total of nine treatments. Comparisons revealed peach roots had differentially expressed genes (DEGs) and gene ontology terms between soil groups, with the S and B groups having a range of 106-411 DEGs and the A group having a range of 19-94 DEGs. Additionally, six modules were identified and correlated (p > 0.69) for six of the nine treatment combinations. This study broadly highlights the complexity of how OM and biological life in the rhizosphere interact with immediate and distant roots and sheds light on how non-homogenous soil conditions can influence peach root gene expression.

Field and numerical investigation of soil hydro-thermal response to the climatic conditions in southern China considering soil heterogeneity

It is essential to investigate soil hydro-thermal behavior to reduce the potential damage to geotechnical constructions caused by varying climatic conditions. In this work, an in-situ monitoring station was built on a clay slope with high groundwater table, situated in Yixing, China. Ten SMT-100 sensors were instrumented on the site to record the evolutions of soil temperature and volumetric water content at various depths. Meteorological information, including relative humidity, air temperature, rainfall, wind speed and solar radiation, and slope runoff was collected. A numerical investigation was also conducted to analyze the variations of soil hydro-thermal response to the recorded climatic conditions by combing coupled hydro-thermal model and soil-atmosphere interaction model. The profiles of soil temperature and volumetric water content suggest that the diurnal changes are limited to depths <40 cm, and the seasonal changes are usually approaching a location deeper than 120 cm. Soil heterogeneity can affect its hydro-thermal response, e.g., higher volumetric water content was observed at the points with lower dry density, which is mainly related to soil water retention capacity. However, appropriate theoretical models to consider soil heterogeneity in the description of soil hydro-thermal properties need to be further investigated.

Methods for Calculating the Resistance of Grounding Devices with Backfilling Special Compositions

Traditional analytical methods for calculating and designing of grounding devices (GDs) in heterogeneous soils can lead to results that do not correspond to those obtained in practice. The empirical coefficients used in calculations of grounding systems given in various literature sources do not always give an explicable and significant discrepancy with the same initial data. In this paper, some well-known methods for calculating the spreading resistance of GDs are considered and the obtained results are compared with experimental data. It is shown that the recommendations and algorithms for calculating the resistance of GDs, presented in the well-known reference literature and regulatory documentation, do not give full and correct description for grounding devices installed in heterogeneous soil. In particular, it is shown that such a factor as the proportional ratio of soils with different resistivity practically does not affect the final result. This fact may mislead specialists, since the results obtained may differ significantly from what is observed in practice after the installation of GDs. The study proposes a calculation method and shows a fairly good convergence of the results with experimental data, and defines a further direction in optimizing calculation methods GDs.

Enhancement on migration and biodegradation of Diaphorobacter sp. LW2 mediated by Pythium ultimum in soil with different particle sizes.

The composition and structure of natural soil are very complex, leading to the difficult contact between hydrophobic organic compounds and degrading-bacteria in contaminated soil, making pollutants hard to be removed from the soil. Several researches have reported the bacterial migration in unsaturated soil mediated by fungal hyphae, but bacterial movement in soil of different particle sizes or in heterogeneous soil was unclear. The remediation of contaminated soil enhanced by hyphae still needs further research. In this case, the migration and biodegradation of Diaphorobacter sp. LW2 in soil was investigated in presence of Pythium ultimum. Hyphae could promote the growth and migration of LW2 in culture medium. It was also confirmed that LW2 was able to migrate in the growth direction and against the growth direction along hyphae. Mediated by hyphae, motile strain LW2 translocated over 3 cm in soil with different particle size (CS1, 1.0-2.0 mm; CS2, 0.5-1.0mm; MS, 0.25-0.5 mm and FS, <0.25 mm), and it need shorter time in bigger particle soils. In inhomogeneous soil, hyphae participated in the distribution of introduced bacteria, and the total number of bacteria increased. Pythium ultimum enhanced the migration and survival of LW2 in soil, improving the bioremediation of polluted soil. The results of this study indicate that the mobilization of degrading bacteria mediated by Pythium ultimum in soil has great potential for application in bioremediation of contaminated soil.

Soil microbial activity profiles associated with organic compost fertilizers in an urban garden

AbstractBiological soil health is recognized as an important component of sustainable agriculture due to microbial biomineralization of nutrients. However, soil health can be difficult to assess consistently across urban agricultural systems due to diverse land use histories, soil heterogeneity, and lack of mechanistic links to agricultural management practices (e.g., recycled compost addition) and crop outcomes. In this study, we characterized soil microbial activity profiles in an urban agriculture system in Minnesota, USA, including microbial abundance, soil respiration, extracellular enzyme activity, and crop yield. Garden plots were fertilized with recycled organic compost (either manure or municipal) at high or low rates (ranging from 2.6 to 39 tons ha−1) targeted to crop N and P demands. Control plots received inorganic fertilizer or no fertilizer. We found that a high application rate of manure compost supported 6–10x higher basal respiration than municipal compost or inorganic fertilizer. Enzyme activity data demonstrated that soil microbial communities exhibited unique profiles of biochemical function that varied among fertilizers of different compositions. Microbial biochemical function predicted 50% of the variability in bell pepper (Capsicum annuum) yield, while soil microbial community size alone was a poor predictor of yield. Yield was highest in plots fertilized with municipal compost, outperforming inorganic fertilizer by threefold. High‐yield plots exhibited higher ratios of N to P enzyme activity compared to those with lower yield. Our findings demonstrate that “more is better” may not necessarily be true regarding soil microorganisms in biological soil health, and that measures of soil microbial biochemical function may be more important.

Tree mycorrhizal associations determine how biodiversity, large trees, and environmental factors drive aboveground carbon stock in temperate forests

Biodiversity, large trees, and environmental conditions such as climate and soil have important effects on forest carbon stocks. However, recent studies in temperate forests suggest that the relative importance of these factors depends on tree mycorrhizal associations, whereby large-tree effects may be driven by ectomycorrhizal (EM) trees, diversity effects may be driven by arbuscular mycorrhizal (AM) trees, and environment effects may depend on differential climate and soil preferences of AM and EM trees. To test this hypothesis, we used forest-inventory data consisting of over 80,000 trees from 631 temperate-forest plots (30 m ​× ​30 ​m) across Northeast China to examine how biodiversity (species diversity and ecological uniqueness), large trees (top 1% of tree diameters), and environmental factors (climate and soil nutrients) differently regulate aboveground carbon stocks of AM trees, EM trees, and AM and EM trees combined (i.e. total aboveground carbon stock). We found that large trees had a positive effect on both AM and EM tree carbon stocks. However, biodiversity and environmental factors had opposite effects on AM vs. EM tree carbon stocks. Specifically, the two components of biodiversity had positive effects on AM tree carbon stocks, but negative effects on EM tree carbon stocks. Environmental heterogeneity (mean annual temperature and soil nutrients) also exhibited contrasting effects on AM and EM tree carbon stocks. Consequently, for the total carbon stock, the positive large-tree effect far surpasses the diversity and environment effect. This is mainly because when integrating AM and EM tree carbon stock into total carbon stock, the opposite diversity-effect (also environment-effect) on AM vs. EM tree carbon stock counteracts each other while the consistent positive large-tree effect on AM and EM tree carbon stock is amplified. In summary, this study emphasized a mycorrhizal viewpoint to better understand the determinants of overarching aboveground carbon profile across regional forests.