Deciphering sample size effect on microbial biogeographic patterns and community assembly processes at centimeter scale

Abstract Revealing the effects of spatial heterogeneity on microorganisms is crucial for the further understanding of microbial diversity, turnover and ecological processes. However, microbial community assembly and the factors that shape it are still unknown at a centimeter scale. To address this gap, we conducted variation partitioning and null model analyses on the microbial community composition of a soil cube, divided into up to 64 sub-cubes, to investigate microbial biogeographic patterns and microbial assembly processes of three centimeter-scale sampling schemes. The results suggested that microbial community was more dispersed and distance decay relationships were more significant in sampling schemes of smaller sample size compared with those of larger sample size. We further investigated the relative importance of ecological processes and demonstrate that bacterial community assembly processes changed from variable selection to homogenous selection as the sample size increased. The importance of spatial distance and micro-environmental variables in shaping and maintaining microbial diversity was emphasized by the dynamics of spatial heterogeneity and environmental filtering. As microorganisms are spatially distributed in soil, this sampling scale dependent diversity and assembly suggests that microbial ecology questions need to be considered in more dimensions than they usually are.