Effects of controlled release potassium chloride application on rhizosphere bacterial community and metabolites under reduced irrigation volume

Though controlled-release potassium chloride (CRK) has been widely used, its effects on the response of microbial community to soil deficit irrigation remain unclear. Here, a three-year greenhouse pot experiment was conducted from 2018 to 2020 to investigate the effects of CRK application under different irrigation levels (conventional irrigation (90 %-100 % field capacity) and 40 % irrigation reduction) on rhizosphere bacterial community and metabolites. The results showed that rhizosphere bacterial richness, diversity, and Alphaproteobacteria, Saccharimonadaceae, Rhizobiaceae, Sphingomonas, Sphingomonadales and Sphingomonadaceae relative abundance was increased by CRK application compared with potassium chloride (KCl) application. Especially under drought conditions, the application of CRK significantly increased bacterial 16S rDNA gene copy number, Chao1 index and Shannon index by 14.1 %, 5.5 % and 0.4 % compared with potassium chloride (KCl) application. Compared with conventional irrigation plus KCl, deficit irrigation plus KCl leads to the dominance of Firmicutes and Actinobacteria. The effects of CRK plus deficit irrigation resulted in a declined relative abundance of the three phyla, e.g., Gemmatimonadales, Frankiales, Nocardioidaceaeand and enrichment of other bacterial phyla, e.g., Proteobacteria, Sphingomonadales, Sphingomonadaceae, Burkholderiaceae, and Alphaproteobacteria compared with deficit irrigation plus KCl. Metabolomic analysis showed that compared with KCl application, CRK application altered soil metabolites. The significantly changed metabolites were those involved in N-glycan biosynthesis, atrazine degradation, retinol metabolism, cutin, suberine and wax biosynthesis, and sphingolipid metabolism. This unique study provides new insights into the mechanism of rhizosphere bacteria adapting to deficit irrigation by the application of CRK.