Shifts in microbial communities with increasing soil fertility across a chronosequence of paddy cultivation in subtropical China

An understanding of microbial community assembly and succession are keys to uncovering mechanisms underlying soil fertility development. The dynamics of microbial communities during a paddy soil chronosequence were investigated by phospholipid fatty acid profiling and amplicon high throughput sequencing. The upper 20 cm were sampled from soils after 5, 15, 30 and 100 years of paddy use and from adjacent barren land. Enzyme activities and contents of soil organic carbon, nitrogen and phosphorus of paddy fields strongly increased compared to barren land, and continued to increase at least up to 100 years of paddy cultivation. The increasing soil trophic status favored bacteria over fungi, and fast-growing copiotrophic bacteria gradually replaced slow-growing oligotrophic bacteria. The genus Ignavibacterium with versatile metabolism was identified as an indicator of the bacterial community in year 30 and 100. The variations of bacterial alpha-diversity tended to stabilize, but species richness continued to increase after 30 years of paddy use. The beta-diversity indicated that bacterial community structure in paddy fields differed from that in barren land. The soils of 5 and 15 years of paddy cultivation clustered into one group separated from the group formed from the year 30 and 100. Redundancy analysis indicated that two stoichiometric ratios: C/N and C/P were the major factors affecting microbial community succession. We conclude that long-term paddy cultivation resulted in changes in biochemical properties and variations in trophic pattern of microbial communities, corresponding to increasing soil fertility.