查看更多>>摘要：? 2022 Elsevier LtdMagnetically responsive minerals were isolated from soil samples using a strong permanent magnet. The isolated materials exhibited peroxidase-like activity using N,N-diethyl-p-phenylenediamine sulfate salt as a substrate. Autoclaving and hot air treatment at 200 °C did not substantially decreased the enzyme-like activity; on the contrary thermal treatment many times caused an increase of peroxidase-like activity. Peroxidase activity measured in soil suspensions is thus due to both the enzymes (peroxidases) of microbial, plant and animal origin, and the inorganic peroxidase-mimetic minerals. We define a new research area called “soil nanozymology” devoted to study of soil-related nanozymes and other enzyme-mimetic materials.
查看更多>>摘要：? 2022Transport of extracellular hydrolytic enzymes in soils has always been a subject of doubt. The considerations against its importance are that (i) enzymes benefit their producers the most when they remain in close proximity; and (ii) enzymes are large molecules with low mobility due to high affinity to fine soil particles and organic matter. However, soil mineral colloids (SMC), to which extracellular enzymes also have an affinity and which are known to facilitate transport of a broad variety of chemicals and microorganisms in soils, can serve as vehicles for enzyme transport as well. Since current literature lacks information on enzyme transport in soils, our goal was to determine whether enzymes are transported and, if so, whether they are transported in a free- or in a colloid-associated form. We conducted column transport experiments with four hydrolytic enzymes, namely, β-glucosidase, acid-phosphatase, cellobiohydrolase, and xylosidase, in soils with contrasting textures. The eluents containing enzymes were applied on top of soil columns, while enzyme activities, SMC, and electrical conductivity were measured in the effluents from the columns. Our results provided evidence of joint enzyme transport with soil colloids. The enzymes associated with the coarse SMC (1 μm < ?) contributed 52–88% of the total enzyme activity in the effluents. The remaining enzyme activity was attributed to the enzymes associated with organic colloids, fine SMC (? < 1 μm) and free enzymes in solution. This study suggested a dual effect of ionic strength in the soil suspension on enzyme activity and their release from soils with soil colloids.
查看更多>>摘要：? 2022 Elsevier LtdPlant and microbial residues are two main sources of soil organic carbon (SOC). While recent studies have extensively examined the distribution of microbial necromass in different ecosystems, how plant residues (in particular, non-lignin components) contribute to SOC accumulation is less clear, especially in forests which make up 50% of the global soil carbon storage. Filling this knowledge gap will help us better understand SOC accumulation patterns and their response to land-use changes. Here, we analyze plant- and microbial-derived biomarkers (including lignin phenols, amino sugars, free and hydrolysable lipids) in the topsoil of major forest types in China and compare their distribution patterns together with the existing data (for lignin phenols and amino sugars) in forests and grasslands distributed globally. At the global scale, forests contain significantly less microbial necromass in SOC compared with grasslands, suggesting higher contribution of plant-derived components to forest SOC. However, plant-derived lignin phenols do not seem to play a major role in SOC accumulation, given their negative relationship with SOC contents. Instead, leaf- and root-derived hydrolysable lipids constitute a much higher proportion of SOC than lignin phenols in the investigated forests of China, even compared to grassland soils. Moreover, in contrast to lignin phenols, both SOC contents and the relative abundance of hydrolysable plant lipids in SOC increase with decreasing soil pH, increasing reactive iron and aluminum contents and with increasing lignin oxidation (indicated by acid-to-aldehyde ratios) in these forest soils. These results suggest that with increasing lignin decomposition, plant lipids and SOC accumulated via (oxyhydr)oxide protection. Collectively, our results demonstrate differential importance of plant-derived components in SOC accumulation in forests versus grasslands and highlight that plant lipids play a more important part than lignin in forest SOC accumulation. Quantitative investigations on the distribution of plant-derived lipids in addition to lignin in forest soils may help to elucidate pathways and hotspots of plant component-dominated SOC accrual.
查看更多>>摘要：? 2022 Elsevier LtdThe discovery of comammox Nitrospira fundamentally changed our perspective of the traditional concept of soil nitrification and has expanded our understanding of the diversity of nitrifying microorganisms. However, the significance and the relative contribution of comammox to nitrification in soil remains poorly understood. Two paddy soils collected in January (winter, nitrification almost stopped) and June (summer, nitrification occurred quickly and at high rates) in 2021 were analyzed for nitrification rates. In situ active nitrifiers were identified by quantifying the amoA gene and transcript abundance to distinguish the relative importance of Ammonia Oxidizing Archaea (AOA), Ammonia Oxidizing Bacteria (AOB) and commomox Nitrospira Clade A and Clade B to ammonia oxidation. Both amoA gene abundance and transcript abundance for comammox were high even in January when nitrification almost stopped and did not increase significantly in summer when nitrification occurred at high rates. On the contrary, AOB transcriptional activity showed a consistent pattern with nitrification, with the amoA gene expression being low for AOB in winter when nitrification almost stopped and increased two orders of magnitudes in summer when nitrification occurred quickly. AOB showed a much higher transcription ratio than AOA. These results indicated that AOB basically drives ammonia oxidation in these paddy soils, and comammox Nitrospira adapts better to low temperature conditions than AOA and AOB. Furthermore, soil water content was identified to be an important factor in shaping comammox clade A activity, but not clade B in these two neutral paddy soils.
查看更多>>摘要：? 2022 Elsevier LtdGrazing by livestock can affect plant biodiversity and topsoil functions. However, experimental evidence on whether these impacts are limited to the topsoil or penetrate into deep layers (via changes in soil environment and resource locations) of soil is lacking, especially for soil microbial biomass and diversity. Here, we used paired grazed and ungrazed (fenced) plots at 10 locations across the Mongolian Plateau to investigate how long-term (>10 years) livestock grazing affects the biomass, diversity, composition, and function of microbial communities in surface (0–20 cm) and deep soil layers (40–60 cm). Livestock grazing increased bacterial diversity by 5–9% in both soil layers but increased fungal diversity by 10% only in the topsoil. Livestock grazing also strongly altered bacterial and fungal community composition in both soil layers. Livestock grazing decreased soil C mineralization rates by 11–25% in both soil layers, and decreased soil N mineralization rates by 16% and bacterial biomass by 20% only in the topsoil. The grazing-induced increase in microbial diversity in both soil layers was mainly explained by the changes in plant C:N ratio and plant biomass rather than by soil abiotic variables, especially for the deep soil layer. The grazing-induced negative effects on ecosystem functions (soil C and N mineralization) were mainly associated with soil abiotic variables together with plant variables or microbial diversity in the surface soil layer and were mainly associated with plant variables and soil microbial diversity in the deep soil layer. Overall, our regional field experiment provides the first evidence that the strong effects of livestock grazing on soil microbial biomass, diversity, composition, and function can penetrate the deep soil in arid and semi-arid grasslands. This knowledge suggests that models should consider the dynamic interactions between land use and both soil microbial diversity and biomass across soil depths in global drylands.
查看更多>>摘要：? 2022 The AuthorsPotential carbon mineralization (Cmin) is a commonly used indicator of soil health, with greater Cmin values interpreted as healthier soil. While Cmin values are typically greater in agricultural soils managed with minimal physical disturbance, the mechanisms driving the increases remain poorly understood. This study assessed bacterial and archaeal community structure and potential microbial drivers of Cmin in soils maintained under various degrees of physical disturbance. Potential carbon mineralization, 16S rRNA sequences, and soil characterization data were collected as part of the North American Project to Evaluate Soil Health Measurements (NAPESHM). Results showed that type of cropping system, intensity of physical disturbance, and soil pH influenced microbial sensitivity to physical disturbance. Furthermore, 28% of amplicon sequence variants (ASVs), which were important in modeling Cmin, were enriched under soils managed with minimal physical disturbance. Sequences identified as enriched under minimal disturbance and important for modeling Cmin, were linked to organisms which could produce extracellular polymeric substances and contained metabolic strategies suited for tolerating environmental stressors. Understanding how physical disturbance shapes microbial communities across climates and inherent soil properties and drives changes in Cmin provides the context necessary to evaluate management impacts on standardized measures of soil microbial activity.
查看更多>>摘要：? 2022 Elsevier LtdThe decomposition of leaf and root litter plays an important role in the cycling of nutrients and carbon (C) in ecosystems. The long-term patterns of mass loss during leaf and root decomposition are well documented, but the long-term responses of mass loss and C quality during the decomposition of these two types of litter to the simultaneous deposition of exogenous nitrogen (N) and phosphorus (P) are not known. We compared the responses of the rate of mass loss, C quality, and the enzymatic and chemical properties of root and leaf litters in the early and late phases of decomposition to N and P addition in a subtropical plantation. N and P addition had delayed effects on root decomposition compared with leaf decomposition. The addition of N and P promoted leaf decomposition in the early phase likely by alleviating the P limitation of microorganisms, indicated by the higher P concentration and lower N/P ratio. The addition of N and P, however, stimulated the decomposition of root litter in the late phase, which was associated with increases in the concentrations of manganese and P in the root residues. The addition of N and P decreased the C quality of the leaf residue in the late phase but had little effect on the C quality of the root residue, even though N and P addition decreased the activity of acid phosphatase and increased the ratio of activities of β-glucosidase to acid phosphatase in the root residue. The decoupled responses of mass loss and C quality during leaf and root decomposition to N and P addition highlight the need to distinguish between leaf and root litter in the late phase of decomposition when evaluating the impact of atmospheric N and P deposition on the cycling of C and nutrients.
查看更多>>摘要：? 2022Direct observations of the complex and highly dynamic metabolic landscapes that affect the structure and functioning of bacterial communities in natural soil are limited by soil opacity and pore space complexity. In this study, we employ community metabolic network models to predict how the emerging bacterial community composition alters its structure and composition as a function of the primary carbon source in both well-mixed and spatially explicit systems. We provide systematic, experimental validation using a synthetic community comprised of four bacterial species grown on prescribed carbon sources and quantify their abundance using qPCR. Results suggest that community members may benefit from trophic interactions or suffer from increased competitive stress depending on the carbon source. The modeling is expanded to consider interactions in soil-like spatial context. Results show emergence of distinct bacterial community compositions as a function of primary carbon sources typical to soil hotspots (carbohydrates or organic acids). The ability to link genetic information with bacterial community trophic interactions in representative soil environments is a critical first step towards attaining predictability of soil ecological functioning.
查看更多>>摘要：? 2022 Elsevier LtdLarge-scale information regarding nitrous oxide (N2O) emissions is needed as an evidence base to underpin land use policy and mitigation approaches. However, the highly variable rates of denitrification make the prediction of N2O emission demanding. Here, we evaluated the role of abiotic and biotic factors on the potential denitrification of Irish soils, in order to identify the key factors regulating potential N2O emissions at a large scale. To do so, we collected 136 soil samples from 32 sites across Ireland, and characterised the soil physico-chemical properties, the prokaryotic and fungal community composition, the abundance of N-cycling genes and evaluated the soil potential nitrification, denitrification and end product N2O/(N2O + N2). We found large differences in soil potential denitrification between sites (up to 41.5 mg N2O–N kg?1 soil day?1) with most of the emissions released in the form of N2O rather than N2. Soils with highest potential nitrification rates also exhibited the highest potential denitrification rates, and similar parameters were linked to both processes. The factors most predictive of soil potential denitrification were soil physico-chemical properties and the prokaryotic community composition. Soil phosphorus content was as important for predicting potential denitrification as was pH and total nitrogen. Soil microbial community structure, rather than denitrifier abundance, was an important predictor of the potential denitrification and the end-product N2O/(N2O + N2). The prokaryotic community composition was more strongly associated with denitrification rates and the resulting end-products than fungal communities. Increased relative abundance of the prokaryotic phyla Actinobacteriota and Crenarchaeota, were positively correlated to complete denitrification. Altogether, these results lay the foundation for a better understanding of the key factors regulating the potential denitrification in soils and identify important properties that enhance prediction of the potential denitrification at larger scales.
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