China-UK joint Red Soil Critical Zone Project. soil metagenome

Most studies on soil microbial distribution tend to focus on topsoil and frequently ignore the microbial communities and their assembly processes in the subsoil and saprolite. Here we examined how the composition, diversity and assembly processes of bacterial communities change with depth through five cores down to a depth of about 4 m located in Red Soil Critical Zone Observatory, Jiangxi province, China. Bacterial richness and phylogenetic diversity significantly decreased at the shallow zone (0-90 cm) and became constant at the deeper zone (90-420 cm), strongly and positively correlating with variations in contemporary factors including dissolved organic carbon (DOC), total nitrogen (TN), total organic carbon (TC) and pH. Bacterial community structure was significantly different between the shallow and the deeper zones, which was shaped by pH, DOC, dissolved total nitrogen (DTN), dissolved organic nitrogen (DON), TN and TC. The distinct bacterial community through soil profiles may also be controlled by historical factors in pedogenic processes. Stochastic and deterministic processes had comparative contributions in controlling community dynamics at the shallow zone whereas the roles of deterministic processes increased and were more important at the deeper zone. These results indicate that distinct bacterial communities and assembly processes exist through deep soil profiles, which could be predicted by contemporary and historical factors during pedogenic processes.