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Arbuscular mycorrhizal fungi (AMF) have been found to help plants adapt to water deficit conditions. However, it still lacks filed evidence on how AMF affect plant physiology and soil microbial communities under natural extreme drought events. Here, we conducted an AMF-inoculation and legume-intercropping (Medicago sativa) field experiment in a forage (Broussonetia papyrifera) monoculture ecosystem, and assessed the effects of AMF on plants and soil microbes during a severe drought event lasting for 40 d. The results showed that the mycorrhizal colonization rate was significantly higher for M. sativa than B. papyrifera. In plots with both B. papyrifera and M. sativa , the physiological properties (e.g., diurnal range of water potential and malondialdehyde concentration) of M. sativa were better in the AMF-inoculation plots than in non-inoculation plots; the trend was opposite for B. papyrifera. AMF-inoculation significantly increased the aboveground productivity of M. sativa by increasing diurnal range of water potential and stem water content during the drought event, resulting in more severe soil water deficits. AMF-inoculation or/and legume-intercropping weakened taxonomic interactions (i.e., edges) and increased the modularity of co-occurrence networks compared with the control. The structural equation model analysis indicated that soil nutrients had a direct positive correlation with soil microbial community composition, whereas soil nutrients and moisture had an indirect negative correlation with soil microbial community diversity by inducing changes in aboveground biomass of B. papyrifera. Overall, AMF-inoculation helps M. sativa acquire water during the drought event, which exacerbates soil water deficits and thereby may increase interspecific water competition between B. papyrifera and M. sativa. AMF-inoculation or/and legume - intercropping maintain the stability of microbial networks by weakening taxonomic interactions and increasing the modularity under the extreme drought event. Our findings improve the understanding of AMF effects on plant-plant and plant-soil interactions under climate extremes. [ABSTRACT FROM AUTHOR]

Soil microbes and fauna as key components of belowground food webs play important roles in energy flux and carbon cycling in terrestrial ecosystems. However, it remains unclear whether forestry management regimes alter the energetic structure of soil food webs and thereby reshape the patterns of soil CO 2 emissions in planted forest. Here, we tested the effects of legume (Cassia alata) addition, understory removal, understory removal with legume addition and all plants removal on energy fluxes through soil food webs and soil CO 2 flux in the wet and dry seasons. We show that soil heterotrophic respiration contributed 36.9–57.8% of total CO 2 flux in the soil. In the dry season, C. alata addition increased soil heterotrophic respiration by 24.6% and 57.3%, respectively, when compared with the control and understory removal treatment. Compared with the understory removal treatment, the total energy flux across the whole food web increased with legume addition (i.e., C. alata addition and understory removal with C. alata addition). Legume addition supported a high proportion of energy flux through herbivorous nematodes, whereas understory vegetation removal supported a high proportion of energy flux through microbivorous nematodes. Less energy fluxes were transferred from basal resources to fungivorous mites and collembolans compared with microbivorous and herbivorous nematodes. The total soil CO 2 flux was positively correlated with metabolic rates of herbivorous and omnivorous-predatory nematodes, and energy fluxes through multitrophic groups. Taken together, legume addition and understory vegetation removal modify the patterns of soil CO 2 emissions via changing nematode metabolic rates and re-shaping the energetic structure of soil food webs. • Nematodes played an essential role in driving energy fluxes through soil food webs. • Legume addition supported a high proportion of energy flux through herbivorous nematodes. • Understory removal supported a high proportion of energy flux through microbivorous nematodes. • Soil CO 2 flux was positively related to energy fluxes through multitrophic groups. [ABSTRACT FROM AUTHOR]

Microbes play important roles in regulating soil phosphorus (P) cycling in agroecosystems. However, little is known about how P-cycling microbes respond to organic and inorganic agricultural managements in terms of their functional and phylogenetic traits. Here, metagenomics was used to determine effects of P-cycling functional genes and taxa on soil P availability in a forage (Broussonetia papyrifera) monoculture ecosystem under organic (inoculating arbuscular mycohrrizal fungi (AMF) and intercropping legume (Medicago sativa)) and inorganic (adding chemical nitrogen (N) and P fertilizers) managements. The results showed that soil available P (AP) in plots with both legume and AMF addition was increased by 54.3 % compared with the control and was1.6–2.4 times higher than in plots with N or P fertilization. The abundance of ppa involved in inorganic-P solubilization was significantly increased after adding both legume and AMF compared with P-addition treatment. Soil alkaline phosphatase activity increased with P fertilizer addition and was positively correlated with soil AP. The abundances of phoA and phnI involved in organic-P mineralization were significantly higher under P fertilization treatment than under N fertilization treatment. Soil total N and AP were the key drivers on interactions among P-transportation genes, organic-P mineralization genes and taxa related to P-transportation. Overall, organic agricultural management increases soil P availability by increasing the potential of inorganic-P solubilization, while inorganic agricultural management regulates P availability via altering the potential of organic-P mineralization. These findings could provide a better understanding of the mechanisms that drive soil P availability under organic and inorganic agricultural managements. • Legume and AMF interactions increased soil P availability by enhancing the potential of inorganic-P solubilization. • Chemical N and P fertilizers addition increased soil P availability by enhancing the potential of organic-P mineralization. • Soil available P and total N drove interactions between functional taxa and genes involved in P-transportation. [ABSTRACT FROM AUTHOR]

• Soil nematode richness is relatively low on inshore islands. • Large island maintains high soil nematode abundance and diversity. • Edaphic and climatic-geographical factors drive variations in soil nematode compositions. Factors that influence the composition and diversity of soil nematode communities on oceanic islands are poorly understood. In this study, we evaluated the soil nematode communities and associated biotic and abiotic factors on five oceanic islands in the north of the South China Sea. We detected 38 nematode genera and found that bacterivores and fungivores were the dominant trophic groups, representing 54.2–70.4% and 15.1–35.3%, respectively, of total soil nematode abundance. The abundances of total soil nematodes and of all trophic groups, maturity, structure indices and nematode diversity were positively correlated with island latitude and area, and were negatively correlated with soil total K and annual temperature. In addition, the abundances of total soil nematodes, bacterivores, herbivores and nematode dominance index were positively associated with soil available K. The abundances of total soil nematodes, fungivores, herbivores, predators and omnivores, maturity, structure, Shannon diversity indices were positively related to soil moisture. Variation partitioning analysis showed that the combination of soil properties and climatic-geographical factors explained more of the variation (26.8–61.5%). The results suggest that larger island can maintain greater nematode diversity than smaller islands due to the greater diversity of habitats on larger island. The key climatic-geographical and edaphic factors affecting soil nematode communities were latitude, annual temperature, soil moisture and total K, respectively [ABSTRACT FROM AUTHOR]

Soil micro-food webs play an important role in ecosystem functions through energy flow; they are strongly influenced by land use types. Previous studies have typically utilized the space-for-time substitution or single-time sampling method to reflect the land-use change effects by comparing differences among existing land-use types. These methods would increase random error. Research on how synchronized land-use change (starting at the same time and place) influences soil ecological processes and functions is urgently needed. Based on a controlled field experiment and seven years of observations, this study explored the effects of land-use change from natural shrubland to cropland (maize), forage land (tall-grass forage), and economic forest land (walnut plantation) on the community structure and energy dynamics of the soil micro-food webs. Cropland simplified the complexity of the soil food webs compared to the other three land-uses. Forage grassland maintained the highest biomasses of soil total microbes, fungi, and arbuscular mycorrhizal fungi. In addition, economic forest land improved the flow uniformity of the micro-food web by increasing energy transfer from resources to bacterivores, fungivores, and herbivores while decreasing herbivore energy flow to omnivores-predators. Omnivore abundance and nematode diversity were important predictors of total energy flux and flow uniformity of the soil micro-food webs, respectively. In addition, omnivores maintained the complexity of soil micro-food webs by promoting interactions among trophic groups through top-down control. Soil organisms are sensitive to the response of agricultural management and planting time, and it may take several years or more to reach a dynamic equilibrium. Different types and levels of ecosystem disturbance (e.g., tillage and no-tillage, fertilizer rates, aboveground biomass removal intensity) may be the major drivers of soil community during land use change. Our findings highlight the importance of conservation agriculture in maintaining soil food web structure and energy flow for future sustainable land uses, and that promoting omnivore abundance is essential for food web complexity and stability. • High level of disturbance in maize cropland suppressed the soil biota and food web energy flow. • Omnivores enhance the soil micro-food web complexity by strengthening the interactions between trophic groups. • Omnivore abundance is good predictor of total energy flux through soil food webs. • Nematode diversity is good indicator of flow uniformity of soil food webs. • Conservation agriculture maintains soil biota and food web energy flow and is a sustainable land use type. [ABSTRACT FROM AUTHOR]