Assessing the use of native rhizobia to improve nitrogen fixation under abiotic stress

Abstract Biological nitrogen fixation by rhizobia bacteria plays a pivotal role in sustainable agriculture by converting atmospheric nitrogen into a form that plants can assimilate, thereby reducing the need for synthetic fertilizers. This process can be dramatically reduced by various abiotic stressors. Native rhizobia strains, which are naturally occurring, may be better adapted to the local soil and climatic conditions, making them more resilient to stress factors such as drought, salinity, temperature extremes, and pH variations compared to commercial strains that may have been developed in and for different environments. This study aimed to compare the efficacy of native rhizobia species with a commercial inoculant and uninoculated controls in maintaining nitrogen fixation under induced stress by delayed planting in field peas over two growing seasons (2021 and 2022) in central South Dakota. Our findings indicate that native rhizobia, while not outperforming the commercial inoculant, demonstrated competitive nitrogen fixation capacities. Overall, total nitrogen fixation was not statistically different between a commercial inoculant and native rhizobia formulations. Planting date emerged as a significant factor influencing nitrogen fixation, with later planting substantially reducing overall effectiveness. These results highlight the potential of native rhizobia as an alternative to commercial inoculants and underscore the need for increased screening throughput and improved methods to assess rhizobia efficacy and nodule competition in field settings.