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Soil microorganisms are vital components of the karst terrestrial ecosystem. However, their responses to the vegetation succession on karst mountain peaks remain unclear as to whether soil microbial diversity and community compositions change with vegetation succession. We investigated the diversity and community compositions of soil bacteria and fungi and associated environmental factors along a vegetation succession from moss crusts (MC) to moss crusts with sparse grasses (MCG) to sparse grasses (G) on karst mountain peaks. The results indicated that soil organic carbon and total nitrogen generally increased, and soil pH changed in the range of 8.19–8.44 and slightly declined with vegetation succession. Overall, there was an increase in microbial biomass along the vegetation succession, with the dominant phyla of bacteria, including Proteobacteria, Acidobacteria, Actinobacteria, Choroflexi, Gemmatiomnadates, Bacteroidetes, and Planctomycetes, and the dominated phyla of fungi, including Basidiomycota and Ascomycota. Notably, both the bacterial and fungal community compositions were different among the three successional stages. Spearman's correction analysis showed that soil organic carbon and total nitrogen had stronger and more significant influences on the soil microbial community compositions compared to soil water content, pH, and C:N ratio. Overall, our results provide evidence for the changes and influencing factors of the microbial community with the succession vegetation on karst mountain peaks. [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]

[Display omitted] • Agricultural residues increase ecosystem multifunctionality. • Agricultural residues increase soil microbe-nematode network complexity. • Soil microbial biomass is positively correlated with ecosystem multifunctionality. • Integrated crop-livestock system obtained the highest economic benefit. The negative environmental impacts of chemical fertilizers have been recognized for a long time, and the returning of agricultural residues to the soil is considered a sustainable agricultural practice. However, few studies have focused on the ecological and economic benefits of returning agricultural residues to the soil simultaneously. Using a 16-year field experiment, we integrally evaluated and compared the ecological and economic benefits of six fertilization practices. The treatments included a no-fertilizer control, conventional chemical NPK fertilization, and partial substitutions of the NPK in chemical fertilizers with a low (30%) or high (60%) level of agricultural residues (straw or cattle manure). The amount of N, P and K inputs remained constant across all fertilization treatments, but the source of N, P and K differed. Ecological benefits were assessed through a study of ecosystem multifunctionality and through a co-occurrence network analysis of the soil micro-food web. Our results showed that applications of agricultural residues increased soil microbial biomass and diversity, soil co-occurrence network complexity, and ecosystem multifunctionality compared with the chemical fertilization alone. The high-level straw substitution treatment supported the greatest ecosystem multifunctionality and soil network complexity. Random Forest regression analysis revealed that soil microbial biomass and fungal diversity were important biological traits associated with ecosystem multifunctionality. The economic benefit was highest when cattle manure was returned to the soil, lowest when crop straw was returned to the soil, and intermediate with chemical fertilization alone. Therefore, the return of cattle manure to the soil provided comprehensive ecosystem services. Our findings increase the understanding of the relationships between economic and ecological effects of returning agricultural residues to the soil. [ABSTRACT FROM AUTHOR]

Soil depth plays a crucial role in shaping the interactions between soil microbes and nutrient availability. However, there is limited understanding of how bacterial, fungal, and protistan communities respond to different soil depths, particularly in the unique geological context and soil properties of karst regions. Organic matter, total nitrogen, and phosphorus, ammonium, nitrate, and plant root biomass, as well as bacterial and fungal abundances, bacterial and protistan diversity were higher in the 0–20 cm soil layer than those in the 20–40 cm and soil-rock mixing layers. In contrast, soil pH was higher in the 20–40 cm and soil-rock mixing layers than that in the 0–20 cm soil layer. The soil exchange of calcium, nitrate, and root biomass were identified as the primary factors regulating microbial assemblages across the depth transect. Moreover, co-occurrence network analysis revealed a greater degree of connectivity between protistan taxa and fungal taxa in the 0–20 cm soil layer than those in the 20–40 cm and soil-rock mixing layers. In contrast, the number of association links between protist-bacteria and bacteria-bacteria was higher in the soil-rock mixing layers compared to the 0–20 cm soil layer. Actinobacteria, Ascomycota, and unclassified protistan taxa were identified as keystones, displaying the highest number of connections with other microbial taxa. Collectively, these results suggested that the increased plant root biomass, coupled with sufficient available nutrient inputs in the upper 0–20 cm soil layer, facilitates strong interactions among fungal and protistan taxa, which play crucial roles in the topsoil. However, as nutrients become less available with increasing depth, competition among bacterial taxa and the predation between bacterial and protistan taxa intensify. Therefore, these findings indicate the interactions among keystone taxa at different soil depths has the potential to generate ecological implications during vegetation restoration in fragile ecosystems. [Display omitted] • Fungal abundance decreased faster than bacterial abundance with soil depth. • Strengthened interactions among fungal and protistan taxa in the 0–20 cm soil layer. • The link numbers between protist-bacteria were increased in the deep soil layer. • Interaction among microbial taxa was regulated by root biomass and soil nutrient. [ABSTRACT FROM AUTHOR]