Structural And Functional Changes In Soil Microbes By Foliar Drift Spray of Seaweed Extract As Revealed By Metagenomics

Abstract Kappaphycus alvarezii seaweed extract (KSWE) is known to enhance crop productivity and impart stress tolerance and our preliminary studies showed their biostimulatory effect on soil bacteria also. Close to one quarter of the foliar spray carried out on maize falls on soil either as drift or from leaf as drip. Hence it was hypothesized, it would profoundly influence soil microbes under stress. An experiment was conducted with five treatments, with or without KSWE application at critical stages of maize under soil moisture stress and compared with an irrigated control. Illumina platform was employed for analysis of V3-V4 region of 16S rRNA gene from the soil metagenome. Total of 345,552 operational taxonomic units were generated which were classified into 55 phyla, 152 classes, 240 orders, 305 families and 593 genera. Shannon’s index and Shannon’s equitability indicated increased soil bacterial diversity by multiple KSWE applications under duress. The abundance of Steroidobacter, Balneimonas, Rubrobacter, Bacillus, Alicyclobacillus, Anaerolinea and Nitrospira genera decreased (49-79%) in drought imposed at V5,10, and 15 stages of maize over the irrigated control, while it significantly improved when followed by KSWE application under drought. Nitrosomonas, Nitrosovibrio, Rubrobacter, Flavobacterium genera and several other taxa which are important for plant growth promotion and nutrient cycling were found to be enriched by KSWE application under drought. Treatments having enriched microbial abundance due to KSWE application under stress recorded higher soil enzymatic activities and cob yield, suggesting the contribution of altered soil ecology mediated by KSWE as one of the reasons for yield improvement.