Responses of endophytic bacterial communities in rice roots to phosphorus deficiency at the seedling stages

Endophytic bacteria play important roles in plant growth and development. However, little is known about the regulation of soil phosphorus (P) nutrition on plant endophytic bacterial communities and their possible functions in relation to plant growth and development. In this study, a phosphorus deficient paddy soil was used for a pot experiment with different levels of P amendments, and high-throughput sequencing of 16S rRNA gene was employed to characterize the endophytic bacterial communities in rice roots. The results showed that at day 7 after transplantation when the seedlings were in the growth resuming period, the rice roots in the P deficiency treatments (P0 and Plow) hosted significantly more endophytic bacteria belonging to Proteobacteria with putative plant growth-promoting functions compared to the Phigh treatment. However, when the seedlings grew for 21 days under P deficiency conditions, the seedling growth was severely restricted, and Firmicutes became the predominant root endophytic bacteria while Proteobacteria became the minority. The putative functions of the abundant Firmicutes were related to detoxification, such as Fe2+ oxidation, NH4+ assimilation and thiosulfate reduction. It was also revealed that the cooperations of the endophytic bacterial communities were clearly strengthened under P deficiency stress at both day 7 and day 21 after transplantation. Thus, when the rice plant is subjected to different levels of P deficiency, as a response, the rice roots might selectively recruit endophytic bacteria to serve the plant growth according to their demand.