Inconsistent Response of Abundant and Rare Bacterial Communities to the Developmental Chronosequence of Pinus massoniana

Abstract

There are differences in the environmental adaptability and regulation of nutrient cycling between abundant and rare bacterial communities during the development of planted forest ecosystems. In this study, we aimed to elucidate the relationships between the soil characteristics and the composition and diversity of abundant and rare bacteria across a chronosequence (i.e., 13-yr, 25-yr, 38-yr, 58-yr-old stands) of Pinus massoniana. Abundant bacterial OTUs, richness, and Shannon index showed a different variation with stand age compared with the rare taxa bacterial community. Both abundant and rare bacterial communities showed significant differences between the 13-yr and 25-yr-old stands, but were similar in the 38-yr and 58-yr-old stands. The dominant phyla were Acidobacteria, Proteobacteria, Chloroflexi, Actinobacteria, and Planctomycetes in both abundant and rare taxa. However, the same phylum of abundant and rare taxa was inconsistent across the four forest ages. Network analysis further demonstrated that rare taxa had a greater network scale and complexity than abundant taxa, which may contribute to buffering the environmental stress. The Mantel test showed that soil pH, nitrogen pool (i.e., MBN, NH4+, NAlkali), and enzyme activities were the key factors that were associated with the changes in abundant bacterial diversity and structure during the development of P. massoniana. However, more soil variables (i.e., pH, SW, MBN, NH4+, NAlkali, AP, nitrite reductase, and sucrase) regulated the rare bacterial communities. Our results indicate that rare taxa are important contributors to soil bacterial community diversity, and their community dynamics responded to changes in soil physicochemical properties significantly distinct from the abundant taxa. We suggest that future studies should focus more on the response of different taxa subcommunities, rather than on the community as a whole, when studying the changes in microbial community dynamics.