Soil property determines the ability of rhizobial inoculation to enhance nitrogen fixation and phosphorus acquisition in soybean

Soil property impacts the efficacy of rhizobial inoculation and rhizosphere processes. However, very few comparative studies have been done to analyze the effects of rhizobial inoculants on plant nitrogen (N) and phosphorus (P) in different soils. The aim of the present study was, therefore, to evaluate N fixation and P acquisition of inoculated soybean (Glycine max) plants in acid and calcareous soils in the field as well as in a pot culture. Our results demonstrate that soil pH determined the effectiveness of rhizobial inoculation. Rhizobial inoculation resulted in greater effects on nodule traits and plant N content in calcareous soil than in acid soil compared with those in non-inoculated plants. A low P availability significantly decreased nodule number and dry weight in both soils relative to P-application treatments. Rhizobial inoculation did not affect root morphological traits and arbuscular mycorrhizal colonization, but strongly increased the amount of carboxylates in the rhizosheath and plant P content. It also increased plant dry weight and yield in calcareous soil. In conclusion, the beneficial effects of rhizobial inoculation on N and P content and soybean growth were particularly pronounced in calcareous soil. The mining strategy of P acquisition was responsible for increases in P content in inoculated soybean plants compared with non-inoculated controls.