The Alleviation of Photosynthetic Damage in Tomato under Drought and Cold Stress by High CO2 and Melatonin
Rong Zhou, Hongjian Wan, Fangling Jiang, Xiangnan Li, Xiaqing Yu, Eva Rosenqvist, Carl‐Otto Ottosen
Abstract
The atmospheric CO2 concentration (a[CO2]) is increasing at an unprecedented pace. Exogenous melatonin plays positive roles in the response of plants to abiotic stresses, including drought and cold. The effect of elevated CO2 concentration (e[CO2]) accompanied by exogenous melatonin on plants under drought and cold stresses remains unknown. Here, tomato plants were grown under a[CO2] and e[CO2], with half of the plants pre-treated with melatonin. The plants were subsequently treated with drought stress followed by cold stress. The results showed that a decreased net photosynthetic rate (PN) was aggravated by a prolonged water deficit. The PN was partially restored after recovery from drought but stayed low under a successive cold stress. Starch content was downregulated by drought but upregulated by cold. The e[CO2] enhanced PN of the plants under non-stressed conditions, and moderate drought and recovery but not severe drought. Stomatal conductance (gs) and the transpiration rate (E) was less inhibited by drought under e[CO2] than under a[CO2]. Tomato grown under e[CO2] had better leaf cooling than under a[CO2] when subjected to drought. Moreover, melatonin enhanced PN during recovery from drought and cold stress, and enhanced biomass accumulation in tomato under e[CO2]. The chlorophyll a content in plants treated with melatonin was higher than in non-treated plants under e[CO2] during cold stress. Our findings will improve the knowledge on plant responses to abiotic stresses in a future [CO2]-rich environment accompanied by exogenous melatonin.