Nighttime transpiration represents a negligible part of water loss and does not increase the risk of water stress in grapevine

Abstract

Nighttime transpiration has been previously reported as a significant source of water loss in many species; however, there is a need to determine if this trait plays a key role in the response to drought. This study aimed to determine the magnitude, regulation and relative contribution to whole plant water-use, of nighttime stomatal conductance (g_night ) and transpiration (E_night ) in grapevine (Vitis vinifera L.). Our results showed that nighttime water loss was relatively low compared to daytime transpiration, and that decreases in soil and plant water potentials were mainly explained by daytime stomatal conductance (g_day ) and transpiration (E_day ). Contrary to E_day , E_night did not respond to VPD and possible effects of an innate circadian regulation were observed. Plants with higher g_night also exhibited higher daytime transpiration and carbon assimilation at midday, and total leaf area, suggesting that increased g_night may be linked with daytime behaviors that promote productivity. Modeling simulations indicated that g_night was not a significant factor in reaching critical hydraulic thresholds under scenarios of either extreme drought, or time to 20% of soil relative water content. Overall, this study suggests that g_night is not significant in exacerbating the risk of water stress and hydraulic failure in grapevine.

Keywords: circadian regulation; grapevine; nighttime transpiration; stomata; stomatal conductance; water loss.