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

Abstract

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 (NO3¯, NH4+ and NO3– + NH4+) 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 (ψw) and osmotic potential (ψs) exhibited a marked decline under salinity stress. The application of the combined form (NO3¯ + NH4 +) 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 (PN), stomatal conductance (gs) 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 plant growth. The inhibition in photosynthesis was relatively greater in ammonium-fed (NH4+) than in nitrate-fed (NO3¯) plants, while the transpiration rate was relatively lower in nitrate-fed plants grown either with or without saline water irrigation. The nitrate form of nitrogen @ 120 kg ha–1 proved best in alleviating the adverse effect of salinity on photosynthesis and transpiration at both the growth stages.