Adaptation strategies of three legumes to soil phosphorus availability in steppes of Inner Mongolia

Aims

Different legumes are distributed across low phosphorus (P) steppe of Inner Mongolia from west to east, this study aimed to investigate the adaptation strategies of different legumes to soil P availability in steppe regions.

Methods

Three legumes (Caragana microphylla, Melissitus ruthenica and Medicago falcata) were grown in pots with soil P additions ranging from 0 to 300 mg P kg⁻¹ soil. Nitrogen (N) and P uptake, growth, rhizosphere processes, and N fixation were determined at harvest.

Results

C. microphylla and M. falcata exhibited increased biomass in response to P addition, with M. falcata demonstrating a more pronounced effect. M. ruthenica responded positively to P addition at 25 mg P kg⁻¹ soil, but P levels above 50 mg P kg⁻¹ soil significantly suppressed its growth and resulted in lower P utilization efficiency compared to M. falcata and C. microphylla. C. microphylla had higher acid phosphatase activity (APase) than the other species, and highest P absorption rate at P addition below 150 mg P kg⁻¹ soil. Low P enhanced succinate exudation in M. ruthenica but not in the other species. P addition promoted P uptake of M. falcata by increasing root length, area and rhizosphere acidification. Low-P deficiency reduced nodulation and N fixation of three legumes in treatments without P addition.

Conclusions

C. microphylla’s higher P absorption rate and APase activity are main adaptive traits for tolerating and adapting to low-P desert steppe soils. Due to M. ruthenica tolerating low-P with high P utilization efficiency traits, it exhibits a fast relative growth rate. M. falcata thrives in high available P soils with accelerated growth. These findings highlight each species’ distinct strategies for nutrient acquisition and adaptation to varying soil P levels, providing scientific insights for sustainable grassland management.