Re-watering: An effective measure to recover growth and photosynthetic characteristics in salt-stressed Brassica napus L.

Salinity is one of major environmental problem which is limiting the agricultural production. This research was conducted to evaluate the effect of re-watering on Brassica napus L., and determination of an appropriate regime for dilution of salted water by studying photosynthetic and growth response of B. napus to salt stress and subsequent re-watering. Plants were treated with NaCl (Nc(1): 2.5, Nc(2): 5, Nc(3): 10; g L-1); Na2SO4 (Ns(1): 2.5, Ns(2): 5, Ns(3): 10; g L-1) and mixed salts treatments (M-1: Nc(1)+ Ns(3); M-2: Nc(3)+ Ns(1); M-3: Nc(2)+ Ns(2); g L-1) and 0 as control, followed by re-watering. In salt stress phase, maximum reduction in net photosynthetic rate (P-N) was noted 79.54%, 80.72%, 84.54%, and 74.84% for Nc(3), Ns(3), M-1 and M-2, respectively, under high concentration levels. To maintain P-N, carbonic anhydrase (CA) activity was stimulated and kept water status stable under low (Nc(1) and Ns(1)) to medium concentration levels (Nc(2), Ns(2) and M-3), and the decreases in P-N under Nc(2), Ns(2) and M-3 were 48.28%, 55.58% and 58.69%, respectively. However, during rewatering phase, growth and physiological parameters were recovered well due to regulation of CA activity under low to medium concentration levels. Relatively as compare to other stress levels more recovery in PN was found after re-watering under medium concentration levels, which were 44.94%, 53.45% and 63.04%, respectively. Though aimed at consideration of high production in B. napus, the best re-watering time was found to be when plants undergo medium concentration levels. Therefore, this study provides a new method for dilution of saline irrigation based on plant physiology.