Changes in Bacterial Community Structure and Nitrogen Cycling Gene Abundance During the Fallow Recovery Phase of Shifting Cultivation in North-East India

We have a good understanding of the recovery of vegetation during secondary succession of the fallow phase of shifting cultivation, but much less knowledge on how this process influences important soil micro-organisms. This study examined changes in the bacterial community (Illumina sequencing) and gene function (qPCR) in fallows of 1–15 years of age in Mizoram, North-east India, and compared them to a natural forest. We found that there was little change in the bacterial community during the first 10 years of fallow recovery but that bacteria in fallows of 15 years of age were more similar to natural forests. In terms of individual phyla, Cyanobacteria were most abundant at the early stages of succession whilst Proteobacteria were positively correlated, and Firmicutes were negatively correlated with soil carbon. There was no change in the abundance of amoA and nosZ genes during succession. Our results indicate that 15 years of fallow regrowth may be sufficient for bacterial communities to recover their community structure as long as this is accompanied by increases in soil carbon and nutrients.