Nitrogen mitigates effect of salinity on plant water relations and photosynthesis in indian mustard ( Brassica juncea )

The interaction between salinity (8 and 12 dS m −1 ) and three levels (40, 80 and 120 kg ha −1 ) of different forms of nitrogen (NO 3 − , NH 4 + and NO 3 − + NH 4 + ) were studied in Brassica juncea cv. RH-30. The plants were salinized with 8 and 12 dS m −1 at 35 and 55 days after sowing. The relative water content (RWC), water potential (Ψ w ) and osmotic potential (Ψ s ) exhibited a marked decline under salinity stress. The application of the combined form (NO 3 − + NH 4 + ) of nitrogen (120 kg ha −1 ) considerably improved the water status and mitigated the adverse effect of salinity on growth. The salinity-induced osmotic effect led to stomatal closure and caused a substantial reduction in net photosynthetic rate (P N ), stomatal conductance (g s ) and transpiration rate (E) at the pre-flowering and flowering stages (45 and 65 DAS). Salinity effects were considerably moderated by additional nitrogen supply, which varied with the source of nitrogen, the level of salinity/fertilizer and the stage of pla...