Discussion:
The results demonstrate the bacterial community dynamics under intensive shifting cultivation, based on culture-dependent and culture-independent approaches. Our data indicate the bacterial diversity in BS, LARS, SARS, and root interior and its successional trend in crop fields of 5, 8, and 20 years fallow cycle.
Culture dependent approach suggests that SARS had the most abundant bacterial population among the rhizosphere niches (Fig.1d). It is also observed that among all the niches, the BS contained the least number of isolates (Fig 1e). The lack of any common isolates may be attributed to undetectably low bacterial isolates in BS compared to the other niches.
In the culture-independent approach for the bacterial abundance based on the OTUs, LARS has greater numbers than other rhizospheric niches (Fig 2d). Though the bacterial phyla were similar in the LARS and BS (Fig 5a, b), the bacterial abundance was more in LARS than BS in both culture-dependent and independent approaches (Fig 2b, 3b). Since the BS samples do not influence the plant’s root, it harbors less bacterial diversity than LARS. While in the case of SARS, root exudates profoundly affect the microbial community. This leads to the selection of a particular bacterial community (40) having greater abundance but less richness than LARS. SARS is the most selective zone for the microbes present in the soil through which they penetrate the plant roots. When we observe the root interior, only a selective bacterial phylum (Proteobacteria ) dominates this niche, which is now called endophytes.