Characterization and application of highly effective rhizobia isolated from Medicago ruthenica in alpine grassland

Background

The symbiotic relationship between legume forages and their rhizobia is highly specific, and the effectiveness of rhizobial inoculants is often limited by local soil and climatic conditions. Therefore, identifying rhizobial strains that are well-adapted to specific environments is crucial for improving nitrogen fixation efficiency.

Methods

Four rhizobial strains were isolated from Medicago ruthenica (L.) Trautv and evaluated for their symbiotic performance with the same host plant. The most effective strain was identified based on key physiological parameters following inoculation. Response surface methodology was then applied to optimize the growth medium for the selected strain, GBXD30.

Results

Inoculation with strain GBXD30 increased plant biomass by 12%, enhanced the number of effective nodules by 3.5-fold, and boosted nitrogenase activity by 0.8-fold, compared to the reference strain USDA1844. Optimization of the fermentation medium via response surface analysis further demonstrated the potential of GBXD30 as a highly effective rhizobial inoculant suitable for alpine grassland conditions.

Conclusions

The targeted selection and application of effective rhizobial strains, such as GBXD30, are critical for maximizing nitrogen fixation in alpine legume forages. These findings offer valuable insights for developing rhizobial inoculants tailored to alpine ecosystems.