Soil Biology & Biochemistry最新文献

While carbon flow through soil decomposition channels is well studied, the associated energy fluxes are less considered. In particular, how microbial substrate and energy turnover are linked to higher trophic levels has hardly been investigated to date. Soil nematode communities can serve as a model group to address this knowledge gap. As important microbial grazers nematodes hold a central position in soil food webs. The present study relates the structure and function of the micro-food web to microbial carbon and energy use efficiency. Microbial biomass (phospholipid fatty acids), activity (substrate-induced growth) and energy flow (substrate-induced heat release) are linked with the nematode fauna, i.e. population density, ecological indices and metabolic footprints. Soils from four agricultural sites in central Europe were compared, either long-term unfertilized or fertilized with farmyard manure.

Environmental conditions (e.g. soil nutrients, moisture) influenced microbial biomass, nematode population density and decomposition channels more than fertilization. While all arable soils were dominated by bacteria, at sites with moderate nutrient status fungi also contributed to carbon and energy flow. The life strategies of microorganisms and nematodes showed a comparable pattern: nutrient-poor unfertilized soils comprised more K-strategists, characterized by an efficient but slow metabolism. Conversely, nutrient-rich soils represented fast cycle systems, dominated by copiotrophic microorganisms and strong r-strategists among nematodes. Across soils, microbial energy use efficiency was quite balanced compared to carbon use efficiency. Remarkably, nematode functional groups were closely linked to microbial substrate turnover efficiency, suggesting nematode faunal analysis as a useful proxy. The nematode Channel Index, a measure for soil decomposition channel activity, is proposed as a tool for mapping microbial carbon and energy turnover.

Germination onset is the first stage in the phenological plant cycle, influenced by abiotic and biotic factors. Both soil and seed microbiota are key drivers of germination, influencing seed storage, dormancy release, and germination rates. Interactions between plants and soil microbes contribute to plant adaptation to their environment. Therefore, plants could benefit more from interacting with soil microbes from the local (‘home’) environment than with those from other origins. As crucial germination drivers, plants may select for specific microbial taxa that provide them with a home-field advantage, regardless of microbial richness and diversity in their surroundings. Here, we looked at the role of seed-associated microorganisms on holm oak (Quercus ilex) germination, whether seed or soil microbes have a greater impact on this process, and how the interaction between seed and soil microbiotas influence holm oak germination. We found that microbes on Q. ilex seeds have a significant effect on germination, with non-sterilised seeds having higher germinated acorns than sterilised ones. Moreover, when co-occurring, soil microorganisms enhance the effect of seed-associated microbes on holm oak germination. Overall, our results evidence a home-field advantage where local soil communities, along with seed-associated microorganisms, enhance Q. ilex germination over that of different soil or plant species, evidencing the importance of local adaptation for plant fitness.

Newly-planted forests require careful management to ensure the successful establishment of young trees; this can include herbicide application, irrigation, fertilization, or a combination of these treatments. The global rise in nitrogen (N) fertilizer application in managed forest plantations is driven by policies aiming at rapid tree growth and carbon sequestration as a strategy to tackle climate change. However, the impact of N-fertilizer on production and consumption of greenhouse gases (GHG), such as carbon dioxide (CO₂), nitrous oxide (N₂O), and methane (CH₄) is poorly understood, particularly when combined with irrigation. As a result, assessing forest GHG balance is key to defining effective climate mitigation strategies through afforestation projects.

This study assessed the response of GHG fluxes to irrigation and fertilization on recently afforested lowland arable land in central England, across loamy and sandy loam soils. The application of 180 kg ha⁻¹ of N via an irrigation system, aimed at enhancing wood production and C sequestration, resulted in an increase of CO₂ and N₂O emissions for both soil types. Particularly, the N₂O emission factors (EF; kg N₂O/kg N applied) for loamy and sandy loamy soils were 3.9% and 2.1%, respectively, higher than the IPCC default estimate of 1% for agricultural and forest land. Furthermore, both sandy loam and loamy soils showed a distinct transition from being CH₄ sinks to sources. Thus, the combined application of irrigation and N-fertilizer had a significant impact on the total Global Warming Potential (GWP), which increased by 34% and 32% for sandy loam and loamy soil, respectively, when compared to their controls. Despite a significant increase in tree growth under fertilized conditions, the offset potential was only partial, highlighting the net contribution to GHG emissions. The outcomes of this study emphasise the potential for significant “carbon-equivalent-debt” from afforestation supported in its early years by irrigation and fertilization.

Revealing the generation and maintenance of biodiversity is a central goal in ecology, but how dispersal, selection, and regional taxon pool size shape soil microbial communities is not well understood. Here, we examined how dispersal and environmental selection affected soil bacterial diversity and their related metabolic functions by leveraging large-scale cross-biome soil surveys of ∼1400 samples from diverse ecosystems across China, including agricultural, forest, grassland, and wetland soils. Our results showed that high dispersal increased α-diversity and decreased β-diversity, whereas strong selection generated the opposite pattern in various ecosystems. This is likely due to dispersal enabling species access to otherwise unreachable habitats, and environmental selection excluding non-adapted species from communities. The α-diversity increased with γ-diversity, whereas β-diversity did not covary. We also showed that bacterial phylotypes positively associated with dispersal and selection exhibited distinct metabolic diversity. Dispersal-induced phylotypes, which were abundant in agricultural soils, exhibited more metabolic diversity in fructose and mannose, starch and sucrose, and nitrogen metabolism. Conversely, selection-induced phylotypes, dominated in wetland soils, were primarily associated with sulfur and methane metabolism. In addition, the complexity of taxon associations increased when communities had higher selection increasing β-diversity. Our study establishes the predictive links of ecological processes to microbial diversity, metabolic functions, and taxon coexistence, thus facilitating a better understanding of the mechanisms underlying biodiversity generation and conservation.

Nitrogen (N) enrichment shapes litter chemistry, subsequently influencing soil invertebrates and litter decomposition. However, there has been a lack of attention to how soil invertebrates respond to changes in litter chemistry and then drive litter decomposition under N enrichment. Here, trait-based approaches were adopted to explore functional responses of Collembola, a crucial and functional group of invertebrates. We conducted reciprocal transplantation of plant litter between ambient N levels (0 kg N ha⁻¹ yr⁻¹) and N enrichment (90 kg N ha⁻¹ yr⁻¹) plots in a field experiment, quantifying Collembola traits and litter mass loss during litter decomposition process. Results showed that N enrichment-derived litter recruited Collembola with long antenna, legs, and strong mandibles in enrichment environment, while Collembola with same traits were recruited by ambient-derived litter in ambient environment. Collembola traits, including antenna to body ratio, leg to body ratio, and mandible width to length ratio, coincided with high litter decomposition rates under N enrichment. Overall, the results provide evidence that Collembola with strong resource acquisition abilities responded to changes in litter chemistry, and such shifts further accelerate litter decomposition under N enrichment. Our findings demonstrate that adopting trait-based approaches to link litter and invertebrates would advance the understanding of ecosystem processes governed by biological regulation under global change.

Microbial communities in many ecosystems are suffering a wide range of environmental stressors induced by anthropogenic perturbations. While the impacts of a single stressor have been extensively estimated in numerous studies, the responses of microbial communities to multiple environmental stressors simultaneously are still poorly understood. In the current study, we investigated the taxonomic diversity, community resistance, and co-occurrence interaction of soil bacterial communities treated with different numbers of environmental stressors by conducting 136 microcosms. We found that the richness and Shannon diversity of the soil community decreased significantly from 1430 to 6.54 in the mono-factor treatments to 920 and 5.77 in the hepta-factor treatments. The counts of nodes and edges of the soil microbial networks decreased with the increasing stressor number, potentially indicating that multiple stressors can reduce the network size. Multiple stressors increased the community resistance potential to environmental disturbance. Additionally, the network cohesion suggested that the cooperative and competitive behaviors between microorganisms were induced by multiple stressors. The observation could be potentially due to the enrichment of the generalists by multiple environmental stressors. Although only a handful of stressors were included, our study still indicated that multiple environmental stressors would lead to diversity loss via deterministic processes.

Reactive oxygen species (ROS) are recognised as pivotal biogeochemical process drivers. However, the factors influencing ROS production in the rhizosphere and their role in pollutant transformation remain elusive. We investigated ROS with a focus on spatiotemporal variations in superoxide radicals (O₂^•−), hydrogen peroxide (H₂O₂), and hydroxyl radicals (^•OH) in the rhizosphere of maize during root development, and elucidated the impact of environmental conditions on ROS production. In-situ visualisation by fluorescence imaging showed that ROS hotspots gradually shifted from seminal to lateral roots during maize growth, indicating that newly developed roots are the major contributors to ROS production. The three types of ROS contents changed with root growth, suggesting that root development regulates ROS production. The ROS contents reached a maximum at 25 °C and 45% maximum field capacity. Both ambient temperature and soil moisture indirectly influenced ROS production by regulating the release of root exudates to induce changes in water-soluble phenols and dissolved organic carbon (DOC). In contrast, ROS content gradually increased with oxygen availability, which directly mediated ROS generation by acting as a precursor. More interestingly, the presence of polycyclic aromatic hydrocarbons (PAHs) significantly enhanced ROS generation, which further promoted PAH removal with a contribution of 31.4–43.3%. These findings provide new insights into the occurrence, distribution, and environmental effects of ROS in the rhizosphere.

Elevated ozone (eO₃) and atmospheric nitrogen (N) deposition are important climate change components that can affect plant growth and plant-soil-microbe interactions. However, the understanding of how eO₃ and its interaction with N deposition affect soil microbially mediated carbon (C) cycling and the fate of soil C stocks is limited. This study aimed to test how eO₃ and N deposition affected soil microbial metrics (i.e., respiration, enzyme activities, biomass, necromass, and community composition) and resulting soil organic C (SOC) fractions in the rhizosphere of poplar plantations with different sensitivity to O₃. Exposure to O₃ and/or N deposition for four years was conducted within a free-air O₃ concentration-enrichment facility. Elevated O₃ reduced soil microbial respiration and biomass C but enhanced the enzymatic acquisition of C (i.e., potential soil hydrolase and oxidase activity) and shifted to a fungi-dominated community composition. These responses suggest that microbial C availability decreased and microbes allocated more energy to obtain C and nutrients from biochemically resistant substrates under eO₃. Elevated O₃ decreased bacterial necromass C and total necromass C, which could explain the observed decreases in mineral-associated organic C and SOC. The effects of eO₃ on soil microbial C availability and community composition were strengthened by N addition, whereas there were no differences in the below-ground effects of eO₃ between the two poplar clones. Taken together, the increased soil extracellular enzyme activities and slightly increased particulate organic C content suggest that the microbial C pump pathway via microbial ex vivo modification was strengthened by eO₃, whereas the pathway via microbial in vivo turnover was weakened, as suggested by the decreases in soil microbial respiration, biomass, necromass, and mineral-associated organic C. Our study provides evidence that aboveground eO₃ effects on trees may affect belowground microbial processing of organic matter and ultimately the persistence of SOC.

Chinese fir (Cunninghamia lanceolata) is one of the most important economic tree species in Central South China. Several decades of successive rotation of C. lanceolata monocultures have resulted in serious ecosystem degradation. Substantial efforts are underway to convert C. lanceolata monocultures to mixed forests to restore ecosystem functions and services. However, it is unclear whether forest restoration will improve soil quality. Soil nematodes were employed as an ecological indicator of soil quality to assess soil food web structure and energy flow along a forest restoration chronosequence. The chronosequence of transformation stages include: (i) early stage C. lanceolata monocultures aged 5, 10, and 20 years old; (ii) mid-stage conifer-broadleaf mixed forest aged over 20 years old; and (iii) late-stage broadleaf forest aged over 40 years old. Our results suggest that forest restoration changed soil nematode abundance, diversity, and community composition in both dry and wet seasons. Abundance of soil nematodes increased progressively along the restoration chronosequence, peaking in the conifer-broadleaf mixed forest. The relative abundance and energy flow of herbivorous nematodes decreased progressively by 25% and 82% with forest restoration stage, respectively. Forest restoration from C. lanceolata to mixed forests increased energy flow from basal resources to fungivorous nematodes and from fungivorous to omnivorous-carnivorous nematodes by 58% and 52%, respectively. Our findings suggest that forest restoration from C. lanceolata monocultures to mixed forests increases soil biodiversity and food web energy flows to trophic groups higher in the food chain. Therefore, converting C. lanceolata plantations to mixed forests has potential to boost forest ecosystem services and promote sustainable forest management.

EL-FAME (ester-linked fatty acid methyl ester), PLFA (phospholipid fatty acid), and qPCR (quantitative PCR) of ribosomal genes are three of the most common methods used to quantify soil microbial communities due to their versatility. The reliability of these three methods has not been simultaneously compared in situations of rapid (in the frame of days and weeks) changes in soil microbial abundances. For this purpose, we (i) incubated badland, cropland, and forest soils with nutrients or antibiotics for 2, 7, 14, and 28 days, (ii) quantified total, bacterial, and fungal abundances through EL-FAME, PLFA, and qPCR methods, and (iii) measured soil basal respiration (as indicator of living biomass). The general dynamic patterns of the three soil microbial fractions in response to soil addition of nutrients and antibiotics were captured by the three methods, which led to strong and positive associations between the abundances of total microorganisms, bacteria, and fungi measured by the three procedures. However, these relationships were stronger between the EL-FAME and PLFA results. Further, soil basal respiration was associated to a higher extent with total, bacterial, and fungal abundances captured by EL-FAME and PLFA analyses than with those measured by qPCR, which suggests that the first two methods are most closely related to the soil living microbial community. In general, dynamics in the abundance of total and bacterial communities were better captured than those of fungi by the three methods. The PLFA analysis seems to perform better than the EL-FAME method in forest soil and in detecting the small antibiotic-induced decreases in microbial abundances. Since the EL-FAME method is cheaper and allows a much faster processing of samples than the PLFA method, and the reliability of both methods is similar in detecting rapid changes of soil microbial abundances, choosing EL-FAME over PLFA may be advantageous in most cases.