Maintaining nitrogen balance under salt stress through enhanced nodule function and antioxidative defense in chickpea

Salinity is a major environmental stress that adversely affects plant growth, nodulation and nitrogen (N) metabolism. This study investigated the physiological and biochemical responses of chickpea (Cicer arietinum L.) genotypes under saline conditions, with a focus on nodule performance, antioxidant enzyme activity and N-fixation efficiency. Ten genotypes, including the salt-tolerant CSG 8962, were evaluated for water relations, ion homeostasis, oxidative stress markers and nitrogen assimilation parameters. Tolerant genotypes maintained higher water potential (Ψw), osmotic potential (Ψs) and relative water content (RWC) in nodules compared to sensitive ones. Salinity-induced oxidative stress, but increased activities of antioxidative enzymes-such as superoxide dismutase, catalase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase, peroxidase and glutathione-S-transferase-contributed to scavenging reactive oxygen species in tolerant genotypes, resulting in lower hydrogen peroxide and malondialdehyde levels and improved membrane stability. Most genotypes (except DCP 92 -3, BG 256 and ICC 4463) maintained the Na⁺/K⁺ ratio below one, a threshold essential for cellular viability. Leghaemoglobin content decreased significantly under salinity, especially in sensitive genotypes. Although nitrate reductase (NR) activity increased with salinity, correlation analysis revealed that N accumulation in shoots was primarily due to biological nitrogen fixation rather than NR-mediated assimilation. These findings suggest that enhanced antioxidant defenses and maintenance of functional nodules are crucial for sustaining N balance in chickpeas under saline conditions.