Correlation of Bacterial Diversity with Fallow periods and rhizosphere niches, RI, BS
The key aspect in the assessment of the microbial growth in the soil ecosystem is soil quality. It has already been reported that the dominant phyla in the soil are Proteobacteria ,Actinobacteria , Acidobacteria , Bacteroidetes ,Firmicutes, and Planctomycetes , but their relative abundance may vary from study site (13, 41, 42). In this study, the microbial diversity is varied with respect to the duration of the fallow periods (Fig 2a, c, 3a). Interestingly, the phylum Proteobacteriaand Bacteroides , common in the nutrient-rich environment (43), were found in the long-term fallow periods. This attribute leads to the genus Pseudomonas (Phylum: Proteobacteria ) showing a negative correlation with other genera in short fallow periods (Fig 4a). Many Proteobacteria genera are responsible for fixing nitrogen and polycyclic aromatic hydrocarbons in the soil (13). Considering the nutrient-rich soil in the long fallow periods, Bacteroides are also dominating phylum in SARS. Acidobacteria is favored in soil with low pH (44). We have observed that the short fallow periods have a lower pH than the long fallow periods (Fig. 8 c-e), which correlated with a decrease in the abundance of Acidobacteria (Fig 4 a, b, c). We have seen a similar pattern for the phylum Actinobacteria,which are mostly gram-positive bacteria that decompose the organic matter in the soil (45). Some of the genera of this phylum form a symbiotic association with the plant’s root and help in nitrogen fixation, phosphate solubilization, and siderophore production (46). The abundance of Actinobacteria in short fallow periods might help the plant roots for taking up nutrients in stress conditions as the soil ecosystems are unstable and less fertile. The condition of short fallow periods is also exploited by the phyla Verrucomicrobia that are oligotrophs and help in methanol oxidation by transferring organic carbon from surface litter layers to mineral soils (47). An insight into the rich microbial diversity in short fallow periods suggest interplay among different bacterial phyla to established dominance and thereby determines the niches of SARS and inside the plant roots as compare to LARS and bulk soil. Among the rhizospheric niches, LARS show a greater bacterial abundance than the SARS, BS, and RI as plants select the specific microbial community in the rhizosphere based on the functional traits beneficial to their performance (40)(Fig 2b,d, 3b). Long fallow periods of more than 10 years have conserved soil health as reported (48, 49) which may be a result of rhizospheric niches near the plant roots formed by the microbial diversity in the short fallow periods which was seen the time series analysis (Fig 6). In general, our result shows that the microbial ecology in the short fallow period’sjhum field plays a significant role in meeting the demand for plant growth.