Nano-biochar regulates soil enzymatic activities and nitric oxide signaling to improve photosynthesis and nutrient balance in Brassica napus under salt stress: Implications for precision agriculture

Salinity stress is a critical abiotic constraint that impairs crop productivity across both irrigated and rainfed agroecosystems. In recent years, nanotechnology has gained considerable attention in agriculture due to its potential to enhance plant tolerance to abiotic stresses. Although nano-biochar (nano-BC) has been widely investigated for improving soil fertility, limited information is available regarding its effects on Brassica napus L. (rapeseed) under salinity stress. The present study evaluated the impact of nano-BC on rapeseed growth, photosynthetic performance, antioxidant defense, osmolyte accumulation, soil enzymatic activities, and soil physicochemical properties under saline conditions. At the flowering stage, plants were treated with two levels of nano-BC (75 g and 150 g plant -1 ). Salinity stress markedly impaired plant performance, as indicated by a 53% increase in hydrogen peroxide (H 2 O 2 ) and a 68% increase in malondialdehyde (MDA), reflecting enhanced oxidative damage and lipid peroxidation. Application of nano-BC significantly mitigated these adverse effects by enhancing antioxidant enzyme activities, including superoxide dismutase (SOD) (71%), peroxidase (POX) (69%), and catalase (CAT) (81%), along with improved flavonoids (16% and 21%), anthocyanins (23% and 31%), and protein content (14% and 19%) respectively over their controls. Moreover, nano-BC application substantially increased soil enzymatic activities and improved key soil physicochemical properties, thereby enhancing nutrient availability and overall soil fertility. Overall, the findings demonstrate that nano-BC effectively alleviates salinity-induced stress by improving plant physiological performance, strengthening antioxidant defense systems, promoting osmoprotectants accumulation, and enhancing soil health. These findings underscore the potential of nano-BC as an effective and sustainable approach for enhancing rapeseed productivity under saline conditions.