Increased ammonification, nitrogenase, soil respiration and microbial biomass N in the rhizosphere of rice plants inoculated with rhizobacteria
Junhua Zhang, Jing Huang, Sajid Hussain, Lianfeng Zhu, Xiaochuang Cao, Chunquan Zhu, Qianyu Jin, Hui Zhang
Abstract
Azospirillum brasilense and Pseudomonas fluoresceins are well-known plant growth promoting rhizobacteria. However, the effects of A. brasilense and P. fluoresceins on the N cycles in the paddy field and rice plant growth are little known. This study investigated whether and how A. brasilense and P. fluoresceins contribute to the N transformations and N supply capacities in the rhizosphere, and clarified the effects of A. brasilense and P. fluoresceins on the N application rate in rice cultivation. Inoculations with A. brasilense and P. fluoresceins coupled with N application rate trials were conducted in the paddy field in 2016 and 2017. The inoculations of rice seedlings included four treatments: sterile saline solution (M0), A. brasilense (Mb), P. fluoresceins (Mp), and co-inoculation with a mixture of A. brasilense and P. fluoresceins (Mbp). The N application rate included four levels: 0 kg N ha–1 (N0), 90 kg N ha–1 (N90), 180 kg N ha–1 (N180), and 270 kg N ha–1 (N270). The results indicated that the Mbp and Mp treatments significantly enhanced the ammonification activities in the rhizosphere compared with the M0 treatment, especially for higher N applications, while the Mbp and Mb treatments greatly enhanced the nitrogenase activities in the rhizosphere compared with the M0 treatments, especially for lower N applications. Azospirillum brasilense and P. fluoresceins did not participate in the nitrification processes or the denitrification processes in the soil. The soil respiration rate and microbial biomass N were greatly affected by the interactions between the rhizobacteria inoculations and the N fertilizer applications. In the Mbp treatment, N supply capacities and rice grain yields showed no significant differences among the N90, N180, and N270 applications. The N application rate in the study region can be reduced to 90 kg N ha–1 for rice seedlings co-inoculated with a mixture of A. brasilense and P. fluoresceins.