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.