Tree species mixture inhibits soil organic carbon mineralization accompanied by decreased r-selected bacteria

Abstract

Mixed-tree species plantations demonstrate higher productivity, soil carbon sequestration capacity, and various soil nutrient contents relative to single-species plantations. Despite the critical role of soil microbes in mediating soil various biogeochemical processes, the effects of tree species mixtures on bacterial community structure and ecological function remain unclear. High-throughput 16S rRNA gene sequencing was used to examine the composition of soil bacterial communities in five single-species plantations and three corresponding mixed plantations. The plantations were established on the same initial substrate, and sampling was conducted in 68 relatively spatially-independent sites. Our results showed tree species mixture significantly altered the soil bacterial community composition and structure, compared with single-species plantations. Especially, Tree species mixture increased the relative abundance of K-strategists (Acidobacteria) and decreased the relative abundance of r-strategists (Proteobacteria and Bacteroidetes). The changes on soil bacterial community composition were largely explained by low molecular weight (LMW; < 250 Da) compounds of dissolved organic C (DOC). Tree species mixture significantly decreased soil C mineralization rates, and there was a negative relationship between soil C mineralization rates and the abundance of K-strategists and a positive relationship for r-strategists. Our results provide preliminary evidence that tree species mixture can significantly alter soil bacterial community composition and their implications on soil organic matter mineralization. This study represents an important step forward in understanding the underlying mechanisms by which plant-microbe interactions influence functions of belowground ecosystems.