Alleviation of salinity stress effects on photosynthesis, nitrogen metabolism and yield of indian mustard by nitrogen fertilization

A study was undertaken to explore the possible alleviation of detrimental effects of salinity on growth, photosynthesis and nitrogen metabolism of Indian mustard through nitrogen fertilization. Experimental plants grown at two levels of nitrogen (0 and 60 kg ha -1 ) were irrigated with waters having 0.2, 5 and 10 dS m -1 EC at weekly intervals from 20 DAS till maturity. Nitrogen application led to significant increase in the concentrations of N, P and K and a decrease in Na concentration in the shoot tissue, under varying salinity levels, both at vegetative and flowering stages. Observations on contents of total chlorophyll, soluble protein, free amino acids, starch, total soluble sugars, nitrate reductase activity and net photosynthetic rates at vegetative and flowering stages revealed adverse effects of salinity on photosynthesis and leaf nitrogen metabolism. However, nitrogen fertilized plants displayed higher photosynthesis and more efficient N metabolism under all levels of salinity at both the growth stages. This led to significant improvement in leaf area development, plant growth and seed yield under salt stress. It was found that seed yield of N fertilized plants even under highest salinity level was comparable with that of non-saline control plants grown without N application. Results indicated that improvement of soil nitrogen status through N application favorably modulated photosynthetic efficiency and carbohydrate metabolism of salt stressed plants besides positive effects on N metabolism which contributed to better performance of plants both under control and salinity stress.