A Comparative Study on Rapeseed Sprayed with Film Antitranspirant Under Two Contrasting Rates of Soil Water Depletion

Rapeseed (Brassica napus L.), as one of the most important oil crops around the world, has been affected by drought considerably, particularly at flowering when crops are most sensitive to water stress. It has been shown that film antitranspirant (AT) can effectively reduce the yield loss of droughted crops if applied at the critical stage. However, the mechanism remains unclear by which AT mitigates drought damage to plants under different rates of water depletion. Two experiments in randomised complete block designs were conducted on spring rapeseed with two levels of irrigation, well-watered (WW) and water-stressed (WS), where slow and fast soil water depletion were imposed during the flowering stage in mesocosms (Expt 1_SD) and pots (Expt 2_FD), respectively, and different concentrations of AT, 0, 0.25%, 0.5%, and 1% and 0, 0.5%, and 1%, were applied. Leaf physiological traits, seed yield, and yield components were determined. The results showed that compared to WW, water stress reduced leaf relative water content (RWC) by 2% and 6% in Expt 1_SD and Expt 2_FD, respectively, and had detrimental effects on stomatal conductance, CO2 assimilation rate, and intrinsic water use efficiency. Following AT application, a positive linear relationship was observed in leaf RWC against AT concentrations, albeit with large variations. In Expt 1_SD, seed dry weight and aboveground biomass increased significantly with increasing AT concentrations, while no yield responses were observed in Expt 2_FD, indicating that soil water status may play an important role in rapeseed responses to AT application regardless of concentrations. Therefore, the timing of AT application needs to consider soil water conditions in addition to the growth development of rapeseed plants.