Physiological and biochemical responses of Dalbergia sissoo to environmental stressors: Implications for tree mortality and health

Dalbergia sissoo (Sheesham), a nitrogen-fixing tree essential to agroforestry systems, enhances soil fertility through leaf litter decomposition and offers notable antimicrobial and antioxidant benefits. However, widespread mortality in northern India—largely due to fungal pathogens and abiotic stresses like drought, waterlogging and nutrient imbalances—poses a serious threat to its sustainability. The physiological and biochemical mechanisms driving this decline remain poorly understood. This study investigates stress responses in declining D. sissoo trees by analyzing oxidative stress markers, antioxidant levels, hormonal shifts and elemental accumulation. Gas chromatography–mass spectrometry (GC-MS) was employed to identify key stress-related metabolites. Results revealed a 29.7 % decrease in ascorbic acid, a 45 % increase in membrane damage and significant hormonal reductions—23.42 % in indole-3-acetic acid and 24.2 % in gibberellic acid. Calcium levels increased by 550 %, along with elevated iron, zinc and nickel, suggesting altered nutrient uptake under stress. Secondary metabolites such as phenolics and flavonoids rose by 36 % and 54 %, respectively, indicating enhanced defense responses, while protein levels declined by 4 %, pointing to impaired primary metabolism. Additionally, soil enzyme activities crucial for nutrient cycling were significantly reduced in affected rhizospheres. These biochemical alterations suggest a shift from growth to defense in response to stress and may serve as early indicators of decline. Understanding these changes can inform better management strategies to enhance tree resilience and support sustainable agroforestry practices.