Phosphorus Mobilization from Native Soil P-Pool upon Inoculation with Phytate-Mineralizing and Phosphate-Solubilizing Bacillus aryabhattai Isolates for Improved P-Acquisition and Growth of Soybean and Wheat Crops in Microcosm Conditions

Microbial transformation of both inorganic and organic forms of soil phosphorus to plant available P is an important trait contributing to plant P-nutrition and growth promotion. The present study was undertaken to evaluate phytate-mineralizing and phosphate-solubilizing Bacillus aryabhattai isolates on plant growth promotion, rhizosphere properties, P-mobilization from native P-pool of soil and acquisition by soybean and wheat crops in Vertisols of central India. Under microcosm conditions, a significant increase in plant growth parameters and plant P content of soybean (R-5 stage) and wheat (panicle initiation stage) crops as a result of inoculation was recorded over un-inoculated control. Similarly, rhizosphere soil properties like activities of fluorescein diacetate, acid and alkaline phosphatase, phytase and microbial biomass-P were also increased with inoculation. These properties were found to be higher with inoculation of isolate MDSR14 followed by MDSR7. At maturity, inoculation with isolates MDSR7 and MDSR14 significantly increased shoot and seed weight, P content and decreased Phytic-P expressed as a percentage of total P content. There was a concomitant depletion in native organic P and acid extractable-P and increase in inorganic P in rhizosphere soil over un-inoculated control indicating mobilization of native unavailable organic P and inorganic insoluble P-pool of soil to available P. Moreover, inoculation also decreased the level of Phytic-P expressed as a percentage of total P content in seeds in soybean and wheat crops as compared to un-inoculated control. The decrease in Phytic-P results in better digestibility and increased feed efficiency and has implication in availability of minerals to human being and animals. The results suggest that B. aryabhattai isolates (MDSR14 and MDSR7) have potential to mobilize native soil P-pool and improve growth, yield and P-assimilation by soybean and wheat crops.