Soil pore size distribution shaped not only compositions but also networks of the soil microbial community

Abstract

Soil pore size and arrangement control the heterogeneous distribution of nutrients, water, and air and, therefore, are likely a superimposed and integrated factor dictating the soil microbial community structure. It is known that soil with more large pores can potentially harbor more diverse microbes under low hydraulic connectivity. Still, there is scant information on how soil pore size distribution (PSD) governs the composition and association of the microbial community. This work examined PSD effects on microbial community compositions and networks via marker gene high-throughput sequencing of both DNA and cDNA. Three soils with a large variation in silt content (~11–73%) and their combinations at different mass ratios were used to enhance the continuity in silt content and thus PSD. Investigations were made under different levels of total pore volume and pore hydraulic connectivity by incubating soils at varied bulk densities and moisture contents for 50 days. The total of six soils was dichotomized into two PSD groups based on soil water retention curves, with PSD-1 of more macro- and mesopores (>30 μm) and PSD-2 of more micropores (<30 μm). Effects of moisture treatments on both fungal and bacterial evenness and Shannon diversity index were pore size group specific, supporting the importance of pore hydraulic connectivity in regulating microbial diversity. PSD-1 soils promoted the proliferation of Betaproteobacteria, Bacteroidetes, and Eurotiales, whereas PSD-2 soils favored Alphaproteobacteria, Sordariomycetes, and Chaetothyriales. Pore hydraulic connectivity slightly and yet significantly affected the microbial relative abundance of PSD-2 soils, with Actinobacteria being more abundant under drier conditions. There were less intra- and interkingdom associations in PSD-2 than PSD-1 soils, and such differences were little affected by pore volume and pore hydraulic connectivity. Our work highlighted PSD-dependent soil microbial distributions and associations, but ecological consequences need to be further examined.