Azoarcus sp. strain KH32C affects rice plant growth and the root-associated soil bacterial community in low nitrogen input paddy fields

摘要

Excessive input of nitrogen fertilizer causes nitrogen pollution in aquatic environments. Utilizing microbial inoculants seems to be effective in decreasing the extent of nitrogen fertilizer application. Genome sequencing analysis of Azoarcus sp. strain KH32C, which was isolated from a paddy-upland rotation paddy field in Japan, showed that the strain may interact with plants. In this study, we examined the effect of inoculation of rice seeds with strain KH32C as a bacterial inoculant in paddy fields without nitrogen fertilization. Rice of three cultivars inoculated with strain KH32C were cultivated in paddy fields with different soil carbon and nitrogen levels. We investigated the growth rate of rice plants and the elemental composition of brown rice. In addition, the bacterial community structures in the rice root-associated soil were examined using molecular genetic analysis. KH32C inoculation resulted in an increase in the rice plant growth rate in the early growth phase with cultivar Nipponbare. Elemental composition analysis showed that the zinc concentration in brown rice of Nipponbare was increased by KH32C inoculation. KH32C inoculation affected the bacterial community in Nipponbare root-associated soil. The community of potential plant growth-promoting bacteria, the majority of which were in the class Alphaproteobacteria, had relatively high abundance in the early growth stage after KH32C inoculation. Our results indicated that strain KH32C can be utilized as a bacterial inoculant with the effect of promoting rice growth and enhancing the zinc content of rice grains in low nitrogen input paddy fields.