Rhizobial biogeography and inoculation application to soybean in four regions across China

Aims: The aim of the study was to survey rhizobial biogeography and to inoculate soybean with selected rhizobia in China to enhance symbiotic nitrogen fixation (SNF).

Methods and results: Biogeography, genetic diversity and phylogeny of soybean rhizobia were surveyed. Inocula were prepared and applied to soybean. Results showed that Bradyrhizobium elkanii and Ensifer fredii were widely distributed in acid and alkaline soils respectively. Available iron was detected as the first determinant for distribution of the two rhizobia and the soybean varieties did not greatly affect the rhizobial compatibility. Geographical latitude and precipitation in June were the main geographical and climatic factors affecting the rhizobial distribution. Inoculation with selected rhizobia increased the nodule number, fresh weight, occupation ratio, seed protein content and soybean yields.

Conclusions: Selection and application of effective soybean rhizobia across China according to biogeography were clarified to promote the SNF, thereby improving soybean yield.

Significance and impact of the study: Rhizobial diversity and biogeography were evaluated systematically in six sites across China. Available iron and soil pH are found to be the most important determinants for the distribution of soybean rhizobia. Inoculation to soybean enhances SNF, positively correlating to the increase in soybean yield and seed protein content.