Long-term afforestation enhances stochastic processes of bacterial community assembly in a temperate grassland

Abstract

Afforestation of grassland is being promoted as a measure to mitigate climate change. While grassland afforestation influences the soil bacterial community structure and composition, the mechanisms involved and impacts of different tree species are poorly understood. In this study, we characterized the soil bacterial community to determine the phylogenetic group assembly after 19 years afforestation of unfertilized grazed grassland with radiata pine (Pinus radiata) and eucalyptus (Eucalyptus nitens). The soil bacterial community was more divergent between grassland and forest, while no differences were observed between P. radiata and E. nitens. Dominant roles of homogeneous selection and drift in soil bacterial community assembly were revealed, and comparable community assembly patterns were observed under both tree species. Afforestation increased the relative contribution of stochasticity (particularly drift) by an average of 22 % compared with grassland, and this was primarily associated with Serratia spp. (Gammaproteobacteria). In addition, the relative abundance of drift was significantly correlated with concentrations of plant-available phosphorus and sulfur in soil. These findings advanced understanding of the impact of land-use change on soil bacterial community composition and assembly.