Stochastic and deterministic assembly processes of bacterial communities in different soil aggregates

Abstract

Soil bacterial community assembly determined by both the niche-based deterministic and the stochastic process. However, at aggregate scale, the contribution and limitation of those theories in soil bacterial community assembly process still unknown. In this study, different aggregate fractions with a water-controllable unit were performed to build a simple system, aiming to (i) exhibit a contrasting bacterial community assembly pattern of aggregate fractions after incubation under different water content, (ii) quantify the variations of bacterial community during incubation caused by niches or deterministic factors of physic-chemical characteristics, and (iii) assess the pore water driven immigration rates of neutral or stochastic processes caused by different aggregate fractions on bacterial community assembly by neutral community model (NCM). We found a significantly time-decay of bacteria community of different soil aggregate fractions during the incubation period. Despite of the decrease of the total OTU amounts, the proportion of the unique OTUs in the aggregates of <0.25 mm and shared OTUs in three soil aggregate fractions increased under both saturated and unsaturated conditions. Microbial communities in aggregates of <0.25 mm were more distinctive enriched the core microbiota of Firmicutes and Proteobacteria than other aggregates, which might relate to the higher availability N and pH value. Under water saturated situation, bacterial migration rate of 0.25–1 mm at the early-stage was higher than others indicated the ineligible role of water-driven bacterial dispersal on bacterial community assembly process. Those results revealed the deterministic and stochastic mechanism of soil bacterial community assembly at aggregate scale, which helps to unravel the mysterious soil habitat.