Legumes under Drought Stress: Plant Responses, Adaptive Mechanisms, and Management Strategies in Relation to Nitrogen Fixation

It is well recognized that the use of chemical fertilizer, particularly N (nitrogen), increases agricultural productivity globally to meet the food demand of the growing population. However, imbalance in use of chemical-N leads to several soil and environmental problems including lost soil organic matter, soil structure, biological activities and fertility, reduced N recovery, N use efficiency, increased soil acidification, greenhouse gas emissions, and the incidence of pest and diseases resulting in diminished crop yield and productivity. To maintain the sustainable agricultural production system and reduce environmental pollution, an alternate source of N is, therefore, a convenient option. Since researchers across the globe are engaged to develop new technologies for the production of more food for an increasing population through sustaining agriculture, therefore, biological nitrogen fixation (BNF) is an excellent solution that can harvest atmospheric N and convert N for plants in naturally available forms. Crops under the Leguminosae family establish root nodules symbiosis with nitrogen-fixing soil bacteria (rhizobia) to fix N through biological nitrogen fixation process. However, drought stress is one of the major abiotic stresses affecting nitrogen fixation in legumes which decreases N accumulation through symbiotic nitrogen fixation (SNF). Despite the significant role of legumes in BNF, the impact of DS on nodule development, stability, and SNF at the physio-biochemical level remains poorly addressed and understood. Therefore, the present chapter focuses on the morphological, physiological, and biochemical responses and tolerance mechanisms of legumes to DS in relation to BNF. The chapter also highlighted the possible breeding and management strategies to enhance drought stress for maximizing yield and nitrogen fixation.