查看更多>>摘要：? 2022 Elsevier LtdBiogeochemical cycles of phosphorus (P) and iron (Fe) are tightly interlinked, especially in highly weathered acidic subtropical and tropical soils rich in iron (oxyhydr)oxides (Fe(III)). The quantitative contribution of the reductive dissolution of Fe(III)-bound inorganic P (Pi) (Fe–P) in low-redox paddy soils may cover the demands of rice plants (Oryza sativa L.) and microorganisms. We hypothesized that microbially-driven Fe(III) reduction and dissolution can cover the P demand of microorganisms but not of the young rice plants when the plants’ P demand is high but their root systems are not sufficiently developed. We grew pre-germinated rice plants for 33 days in flooded rhizoboxes filled with a paddy soil of low P availability. 32P-labeled ferrihydrite (30.8 mg kg?1) was supplied either (1) in polyamide mesh bags (30 μm mesh size) to prevent roots from directly mobilizing Fe–P (pellets-in-mesh bag treatment), or (2) in the same pellet form but without a mesh bag to enable roots accessing the Fe–P (pellets-no-mesh bag treatment). Without mesh bags, Pi was more available leading to increases in microbial biomass carbon (MBC) by 18–55% and nitrogen (MBN) by 4–108% in rooted soil as compared to Pi pellets not directly available to roots. The maximum enzyme activities (Vmax) of phosphomonoesterase and β-glucosidase followed this pattern. During rice root growth, day 10 to day 33, MBC and microbial biomass phosphorus (MBP) contents in both rooted and bottom bulk (15–18 cm) soil gradually decreased by 28–56% and 47–49%, respectively. In contrast to our hypothesis, the contribution of Fe–P to MBP remarkably decreased from 4.5% to almost zero from 10 to 33 days after rice transplantation, while Fe–P compensated up to 16% of the plant P uptake at 33 days after rice transplantation, thus outcompeting microorganisms. Although both plants and microorganisms obtained Pi released by Fe(III) reductive dissolution, this mechanism was not sufficient for the demand of either organism groups.
查看更多>>摘要：? 2022Soil organic matter (SOM) is a fundamental resource to humanity for the many ecosystem services it provides. Increasing its stocks can significantly contribute to climate change mitigation and the sustainability of agricultural production. Elucidating the mechanisms and drivers of the formation of the main components of SOM, particulate (POM) and mineral associated (MAOM) organic matter, from the decomposition of plant inputs is therefore critical to inform management and policy designed to promote SOM regeneration. We designed a two-tiered laboratory incubation experiment using 13C and 15N labeled plant material to investigate the effects of the physical nature (i.e., structural versus soluble) of plant inputs as well as their chemical composition on (1) the pathways of SOM formation, (2) the soil microbial community and chemical diversity, and (3) their interaction on the stabilization efficiency of litter-derived C in POM and MAOM, in a topsoil and a subsoil. We found that: i) the physical nature of the plant input (structural vs soluble) drove both the pathways and efficiencies of SOM formation; ii) POM formation from the decomposition of structural residues increased in efficiency the more decomposed were the residues, and linearly with soil microbial and chemical diversity, the latter only for subsoil; ii) more input-derived C and N were retained in subsoil because of both higher stabilization in MAOM and POM, and slower residue decay. Our results also confirm the importance of direct sorption of soluble inputs to silt- and clay-sized minerals for the formation of MAOM in bulk soils. Taken together these finding suggest that the highest potential for SOM accrual is in subsoils characterized by higher C saturation deficit, from the separate addition of decomposed residues and soluble plant inputs.
查看更多>>摘要：? 2022 Elsevier LtdWe still lack crucial knowledge about the contribution of plant vs. microbial residues to specific SOM pools, particularly the relative contribution of arbuscular (AM), ectomycorrhizal (ECM), and saprotrophic (SAP) fungi. We investigated sources of particulate and mineral-associated organic matter (POM and MAOM) around trees with distinct mycorrhizal types, Liriodendron tulipifera (AM-association) and Quercus alba (ECM-association), in a temperate deciduous forest in Indiana, USA. Combining 13C and 15N natural abundance analyses with measurements of microbial residues using amino sugars, the isotope signatures of large, medium and small-sized POM and MAOM fractions were compared with those of leaves, roots and biomass of mycorrhizal and saprotrophic fungi. A Bayesian inference isotope mixing model calculated sources of C and N to SOM fractions. While the isotope composition of POM resembled that of plants, MAOM was close to fungal values. This was confirmed by mixing model calculations and microbial residue analysis, which additionally and independent from tree partner suggested saprobic fungi contributing with 4–53% to POM and 23–42% to MAOM, as opposed to ECM contributions. Our results suggest fungal, not plant residues, as the source of the most putatively stable OM pool; thus, altering fungal communities may enhance efforts to increase long-term soil C storage.
查看更多>>摘要：? 2022 Elsevier LtdThe newly added exogenous organic matter may change the decomposition rate of native soil organic matter (SOM) by the priming effect (PE) and further impact the terrestrial carbon (C) balance. Earth system models have not yet considered the distinct responses of soil C pools with different stability and turnover rates to PE. We addressed this knowledge gap by incubating three soils (from the same site but at different stages of SOM decomposition) developed under C3 vegetation with or without the addition of maize straw (C4) and its pyrolysis product-biochar (C4) in a 180 d-incubation at 22 and 32 °C. The three soils were sampled from 15-year old-field, 15-year bare-fallow, and 23-year bare-fallow plus additional laboratory 815-d incubation, representing active (old-field soil) and relatively resistant (two bare-fallow soils, with more stable fraction and less labile fraction) soil C pools, respectively. Soil-derived CO2 was distinguished by a two-component mixing model using a natural 13C isotopic tracing method (C3 vs. C4). The PE was by 30%–239% higher in two bare-fallow soils than in old-field soil regardless of types of new C input (straw and biochar) or temperatures (22 and 32 °C), and the straw-induced PE was by 90%–297% higher than the biochar-induced PE regardless of soils or temperatures. Moreover, the straw-induced PE was not altered with warming in the three soils, but the biochar-induced PE was significantly decreased by warming, especially in old-field soil. These results suggested that the PE varies with soil C pools with different stability. The relatively resistant soil C pool is more vulnerable to PE than the active soil C pool, but the resistant soil C pool can sequestrate more exogenous C and result in higher soil C storage than the active soil C pool, at least in the short term. In addition, more biochar-C can be retained in these soils than straw-C, but this difference would decrease with warming. Overall, this study suggests that future experimental and modeling studies should pay attention to the distinct vulnerability of soil C pools with different stability to PE and warming for accurately predicting soil C dynamics.
查看更多>>摘要：? 2022 Elsevier LtdInterspecific competition between ammonia-oxidizing archaea (AOA) and bacteria (AOB) has been documented, however, its significance in niche differentiation between these nitrifiers under ammonia-rich conditions remains elusive. A network-oriented microcosm incubation study was established to improve our understanding of their interspecific competition. A high ammonium concentration was maintained during the incubation by regularly supplementing urea, and the growth of AOB was retarded to different extents using the AOB inhibitors 1-octyne (OC) and 3,4-dimethylpyrazole phosphate (DMPP) as amendments. In parallel, a 13CO2-stable isotope probing (SIP) incubation study was conducted to investigate the metabolic activity of AOA and AOB under ammonium-rich conditions, with and without DMPP amendment. The results of the network-oriented microcosm incubation indicated that the growth of AOA was highly and negatively correlated with the growth of AOB (r = ?0.94, P < 0.001). Network analysis of the whole prokaryotes showed that the majority of AOA phylotypes formed a module independent of AOB phylotypes, indicating their distinct niche preferences. In another distinctive module, we found the remaining AOA to have a coexclusion pattern with AOB, indicating a competitive relationship and a positive connection between AOB and many taxa capable of nitrite/nitrate metabolism, in particular denitrification. The SIP study confirmed that all AOA and AOB phylotypes retained in the network were autotrophically active. It was also shown that the phylotype susceptible to AOB competition was closely related to Nitrososphaera viennensis EN76. Overall, the results demonstrate that both niche preference and interspecific competition contribute to niche partitioning between AOA and AOB. Our results also showed that a tight connection between AOB and other nitrogen-cycling microorganisms may be responsible for substantial nitrogen loss.
查看更多>>摘要：? 2022 Elsevier LtdShrubification is widespread in global grasslands. However, whether shrubification promotes the mineralization of soil organic carbon (SOC) remains uncertain. We compared sizes and compositions of soil non-cellulosic and amino sugar pools, soil stoichiometry, SOC decomposition and its temperature sensitivity between herbaceous and shrubby patches in alpine meadows on the Qinghai-Tibetan Plateau. The SOC content and soil stoichiometric C/P and N/P ratios in shrubby patches markedly increased with increasing plant size compared with herbaceous areas, indicating the increased P limitation to microorganisms relative to C and N with SOC accumulation under shrubs. The mass ratio of galactose plus mannose to arabinose plus xylose in the non-cellulosic carbohydrate pool of plant input was higher under shrubs than under grasses but was generally similar in soils between herbaceous and shrubby patches. This suggests the retarded microbial transformation of plant-derived carbohydrates under shrubs. Shrubs decreased accumulation of microbial necromass in SOC but increased the proportion of fungal origin in the microbial necromass. Lower total CO2 efflux per unit mass of SOC at either 15 °C or 25 °C from shrubby than from herbaceous patches over the 76-day incubation was mainly associated with the increased soil C/P or N/P ratio under shrubs. Shrubs decreased temperature sensitivity of SOC decomposition compared with grasses only at 20–40 cm soil depth, where microbial-synthesized substances had greater dominance over organic matter than at 0–20 cm depth and were less abundant under shrubs relative to grasses. Our findings show that increased P limitation to microorganisms in shrubification resulted in the decreased SOC decomposability and indicate that microbial-synthesized substances determined the temperature sensitivity of SOC mineralization. Therefore, shrubification mitigates CO2 emissions in grasslands by decreasing SOC mineralization and its temperature sensitivity in the context of global warming.
查看更多>>摘要：? 2022Fungi influence agricultural production due to their key roles in soil biotic and abiotic processes. However, there is limited knowledge of their status at scales relevant for farm management and policymaking. We examined the relationships between commonly applied agricultural practices and soil fungal diversity in 78 arable fields in Estonia. We used DNA metabarcoding of the ITS and SSU regions to detect soil total, arbuscular mycorrhizal, pathogenic and saprotrophic fungal diversity. We also collected field management data and assessed the proportion of field area influenced by uncropped landscape elements. We found that fertilizer type and pesticide use frequency, but not tillage regime, were important determinants of soil fungal diversity in fields. We also found that soil fungal richness was generally higher when a larger proportion of the field was influenced by uncropped landscape elements. Importantly, we found significant interactions between fertilization type and frequency of pesticide use, which, in some cases, resulted in amplified negative effects on soil fungal species richness. Our work highlights the need for simultaneous assessment of multiple landscape and management impacts on soil biota.
查看更多>>摘要：? 2022Reduction in snow cover is a prominent aspect of global change. Freeze–thaw cycles (FTCs) of different amplitudes and durations in soil due to insufficient thermal insulation may alter microbial diversity and key ecological functions mediated by microorganisms. These changes could then further alter the cycling of material and energy in the ecosystem. Yet despite many assessments, the impact of FTCs upon microbial diversity remains poorly understood. Here, 546 observations from 61 published studies were collected for a global meta-analysis with the objective to explore how soil microbial diversity and C and N dynamics it drives respond to FTCs. The results showed that: in general, FTCs did not lead to a reduction of microbial α-diversity, but they did reduce levels of soil microbial biomass carbon, microbial biomass nitrogen, and phospholipid fatty acid by 7%, 12%, and 11%, respectively; they also significantly changed the microbial community structure. FTCs did not significantly affect the α-diversity of bacteria and fungi, but community structures of both were changed significantly, with that of the bacteria more sensitive to FTCs. FTCs were responsible for a 6% decrease in functions related to C, N cycling, which could be explained by the changes found in microbial biomass and community structure. FTCs could also indirectly impact microbial biomass via changed pH and soil water content (SWC). The response of microbial community to FTCs was related to the FTC frequency, freezing temperature and sampling time. FTCs had a large effect on the C and N pool components and fluxes in soil. It is particularly noteworthy that FTCs drove a 137% increase in N2O emission. Further, the changes in pH and SWC directly affected the C and N pool components and fluxes. The results of current meta-analysis deepen the comprehensive understanding of the effects of FTCs on the soil microbial community and C and N dynamics it mediated, and provide a reference for subsequent research in terms of experimental scheme and scientific issues requiring close attention.
查看更多>>摘要：? 2022Protists, in particular bacterivores, are essential players in the rhizosphere; thus, how their interactions with bacteria and fungi affect plant productivity and soil nutrient cycles warrants more attention. Using next-generation sequencing of the 18 S rRNA gene, we investigated the distribution of two major protistan phyla, Cercozoa and Endomyxa, across four seasons, and four soil compartments - rhizosphere, root, soil and litter. The sampling was replicated in two forests in Norway and the Czech Republic, in order to test our results across biogeographic scales. Compartment had a major influence in shaping protistan communities, over and above spatial distance and seasonal variation. Protistan diversity was highest in the bulk soil while lowest in the roots, suggesting that the plants select for restricted assemblages of protists. Accordingly, only the root compartment harboured a subset of the bulk soil protistan diversity. In addition, protistan communities showed markedly different distributions according to their feeding modes, with opposite patterns for bacterivores versus omnivores and eukaryvores. The small bacterivorous flagellates (mostly Glissomonadida) were more abundant in roots, while the larger amoeboid eukaryvores (e.g. some of the Cryomonadida and vampyrellids) dominated in soil and in the rhizosphere, and the omnivores (e.g. Euglyphida and part of the Cercomonadida), also large and mostly amoeboid, were more abundant in litter. The current view of the soil microbiome is mostly focused on bacteria and fungi: this detailed study on the community distribution of protists according to their feeding modes reveals the essential role they play in each of the soil compartments, an essential precondition for a detailed understanding of the soil food web and nutrient cycling in forest.
查看更多>>摘要：? 2022 The AuthorsAgricultural intensification and extreme weather events can represent considerable stress to soil microorganisms and their functions by influencing the key players behind the degradation of soil organic matter. A better understanding of the diversity and abundance of microbial functional genes that predict the functional potential of soils, can link the microbial communities to their key ecosystem functions. As there are still gaps in understanding how the functional genetic diversity behind microbial extracellular enzymes is influenced by events like drought and soil carbon management, an agricultural experiment over a range of different climatic conditions and soil properties was set-up across Europe. In Sweden, Germany and Spain, fields with varying levels of soil organic carbon were subjected to a short-term experimental drought. The diversity and composition of genes encoding for carbohydrate-related extracellular enzymes were determined using a ‘captured metagenomics' technique. Functional gene diversity differed among the European regions and to a range of soil factors such as organic carbon and water content. The functional and taxonomic gene composition significantly differed between the climatic regions, while an effect of short-term drought was only observed in Germany. The results indicate that some soil microbial communities and their functional genes displayed a certain degree of resistance. The results suggest that soil microbial communities respond differently to short-term drought mainly due to regional adaptations to already dry environments and differences in their soil physicochemical properties.
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