Bacterial succession along a long-term chronosequence of paddy soil in the Yangtze River Delta, China

Abstract

Conversion of tidal wetlands into paddy soils is an ancient and prevalent agricultural practice to meet increasing demand of food in the Yangtze River Delta of China, a coastal region where paddy soils originated. However, the impacts of tidal wetland reclamation and continuous rice cultivation at long time scales on soil bacterial communities remains poorly understood. In this study, we investigated temporal dynamics of bacterial communities using 16S rRNA gene pyrosequencing to delineate the patterns and drivers of soil bacterial succession along a long-term (2000 years) chronosequence of paddy field since reclamation from tidal wetlands. The results exhibited orderly changes in soil physicochemical characteristics and bacterial community composition with increasing rice cultivation time, indicating the occurrence of paddy soil development and bacterial succession since reclamation from tidal wetlands. Soil bacterial diversity significantly increased after reclamation of tidal wetlands. Succession of bacterial community composition was primarily linked with significant decrease in the relative abundances of Gammaproteobacteria and Planctomycetes and increase in those of Alphaproteobacteria and Firmicutes. Further analysis showed that long-term rice cultivation led to the enrichment of certain populations such as Rhodospirillaceae (within the class Alphaproteobacteria) and Clostridiaceae (within the phylum Firmicutes), which are potentially beneficial to higher rice yields. Canonical correspondence analysis indicated that at the time scale of millennia, the shift of bacterial community structure was mainly driven by the changes of soil physicochemical properties, especially cation exchange capacity and pH during paddy soil development. Overall, we demonstrate an orderly shift of soil bacterial communities towards higher productivity along with a 2000-year development of paddy soils after the tidal wetland reclamation, which was primarily associated with soil physicochemical alterations with time, and suggest that such chronosequence of paddy soils can serve as a test bed to delineate the relationship between microbial community and soil functions, particularly crop productivity.