Soil microbiota play a critical role in soil biogeochemical processes and have a profound effect on soil functions. Recent studies have revealed microbial co-occurrence patterns in soil microbial communities, yet the geographic pattern of topological features in soil microbial co-occurrence networks at the continental scale are largely unknown. Here, we investigated the shifts of topological features in co-occurrence networks inferred from soil microbiota along a continental scale in eastern China. Integrating archaeal, bacterial and fungal community datasets, we inferred a meta-community co-occurrence network and analyzed node-level and network-level topological shifts associated with five climatic regions. Both node-level and network-level topological features revealed geographic patterns wherein microorganisms in the northern regions had closer relationships but had a lower interaction influence than those in the southern regions. We further identified topological differences associated with taxonomic groups and demonstrated that co-occurrence patterns were random for archaea and non-random for bacteria and fungi. Given that microbial interactions may contribute to soil functions more than species diversity, this geographic shift of topological features provides new insight into studying microbial biogeographic patterns, their organization and impacts on soil-associated function.

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Microorganisms play an important role in soil phosphorus (P) cycling and regulation of P availability in agroecosystems. However, the responses of the functional and ecological traits of P-transformation microorganisms to long-term nutrient inputs are largely unknown. This study used metagenomics to investigate changes in the relative abundance of microbial Ptransformation genes at four long-term experimental sites that received various inputs of N and P nutrients (up to 39 years). Long-term P input increased microbial P immobilization by decreasing the relative abundance of the P-starvation response gene (phoR) and increasing that of the low-affinity inorganic phosphate transporter gene (pit). This contrasts with previous findings that low-P conditions facilitate P immobilization in culturable microorganisms in short-term studies. In comparison, long-term nitrogen (N) input significantly decreased soil pH, and consequently decreased the relative abundances of total microbial P-solubilizing genes and the abundances of Actinobacteria, Gammaproteobacteria, and Alphaproteobacteria containing genes coding for alkaline phosphatase, and weakened the connection of relevant key genes. This challenges the concept that microbial P-solubilization capacity is mainly regulated by N:P stoichiometry. It is concluded that long-term N inputs decreased microbial P-solubilizing and mineralizing capacity while P inputs favored microbial immobilization via altering the microbial functional profiles, providing a novel insight into the regulation of P cycling in sustainable agroecosystems from a microbial perspective.

Background: Microbial interactions shape the structure and function of microbial communities; microbial co-occurrence networks in specific environments have been widely developed to explore these complex systems, but their interconnection pattern across microbiomes in various environments at the global scale remains unexplored. Here, we have inferred an Earth microbial co-occurrence network from a communal catalog with 23,595 samples and 12,646 exact sequence variants from 14 environments in the Earth Microbiome Project dataset. Results: This non-random scale-free Earth microbial co-occurrence network consisted of 8 taxonomy distinct modules linked with different environments, which featured environment specific microbial co-occurrence relationships. Different topological features of subnetworks inferred from datasets trimmed into uniform size indicate distinct co-occurrence patterns in the microbiomes of various environments. The high number of specialist edges highlights that environmental specific co-occurrence relationships are essential features across microbiomes. The microbiomes of various environments were clustered into two groups, which were mainly bridged by the microbiomes of plant and animal surface. Acidobacteria Gp2 and Nisaea were identified as hubs in most of subnetworks. Negative edges proportions ranged from 1.9% in the soil subnetwork to 48.9% the non-saline surface subnetwork, suggesting various environments experience distinct intensities of competition or niche differentiation. Conclusion: This investigation highlights the interconnection patterns across microbiomes in various environments and emphasizes the importance of understanding co-occurrence feature of microbiomes from a network perspective.

One of the proposed mechanisms through which plant growth-promoting rhizobacteria (PGPR) enhance plant growth is the production of plant growth regulators, especially cytokinin. However, little information is available regarding cytokinin-producing PGPR inoculation on growth and water stress consistence of forest container seedlings under drought condition. This study determined the effects of Bacillus subtilis on hormone concentration, drought resistance, and plant growth under water-stressed conditions. Although no significant difference was observed under well-watered conditions, leaves of inoculated Platycladus orientalis (oriental thuja) seedlings under drought stress had higher relative water content and leaf water potential compared with those of noninoculated ones. Regardless of water supply levels, the root exudates, namely sugars, amino acids and organic acids, significantly increased because of B. subtilis inoculation. Water stress reduced shoot cytokinins by 39.14 %. However, inoculation decreased this deficit to only 10.22 %. The elevated levels of cytokinins in P. orientalis shoot were associated with higher concentration of abscisic acid (ABA). Stomatal conductance was significantly increased by B. subtilis inoculation in well-watered seedlings. However, the promoting effect of cytokinins on stomatal conductance was hampered, possibly by the combined action of elevated cytokinins and ABA. B. subtilis inoculation increased the shoot dry weight of well-watered and drought seedlings by 34.85 and 19.23 %, as well as the root by 15.445 and 13.99 %, respectively. Consequently, the root/shoot ratio significantly decreased, indicative of the greater benefits of PGPR on shoot growth than root. Thus, inoculation of cytokinin-producing PGPR in container seedlings can alleviate the drought stress and interfere with the suppression of shoot growth, showing a real potential to perform as a drought stress inhibitor in arid environments.

Understanding biogeographic patterns is a precursor to improving our knowledge of the function of microbiomes and to predicting ecosystem responses to environmental change. Using natural forest soil samples from 110 locations, this study is one of the largest attempts to comprehensively understand the different patterns of soil archaeal, bacterial, and fungal biogeography at the continental scale in eastern China. These patterns in natural forest sites could ascertain reliable soil microbial biogeographic patterns by eliminating anthropogenic influences. This information provides guidelines for monitoring the belowground ecosystem’s decline and restoration. Meanwhile, the deviations in the soil microbial communities from corresponding natural forest states indicate the extent of degradation of the soil ecosystem. Moreover, given the association between vegetation type and the microbial community, this information could be used to predict the long-term response of the underground ecosystem to the vegetation distribution caused by global climate change.

Understanding the impact of grazing patterns on grassland production is of fundamental importance for grassland conservation and management. The objective of this study is to obtain an understanding of the trade‐offs between aboveground biomass and belowground biomass, which are influenced by environmental factors in free grazing (FG) and grazing exclusion (GE) alpine grasslands on the Tibetan Plateau. We explored the relationships between the trade‐off and environmental factors using correlation analysis, a generalized additive model and a structural equation model, and then found that the key factors that determine trade‐off showed differences in FG and GE grasslands and that the final structural equation modeling result explained that 96% (path coefficient = 0.96) and 65% (path coefficient = 0.65) of the variations in the trade‐off were due to FG or GE classifications, respectively. The results demonstrated that soil organic carbon, soil carbon/soil nitrogen, and soil available nitrogen affect the trade‐off between aboveground and belowground biomass in FG grasslands more obviously than in GE grasslands. However, the effects of growing season temperature on the trade‐off were insignificant, −0.218 and −0.181 in FG and GE grasslands, respectively. FG increased the soil bulk density, which resulted in an alteration in the soil pore size distribution and a greater resistance to root penetration. In addition, FG affected the level of soil nutrition, which will affect the nitrogen mineralization of decomposition and absorption, as well as the root biomass. Consequently, this study can provide guidance to improve the quality of grassland.