Heat wave delays the drought recovery of leaf physiology in Solanum lycopersicum seedlings

Background/Question/Methods Heat waves in combination with drought are predicted to occur more frequently with climate warming, yet their interactive effects on crop carbon and water balance are still poorly understood. In particular, how photosynthesis and water relations would recover from the combined stress remains largely uncertain. Improved understandings on the capacity of crops to cope with the combined heat-drought stress will provide insights into more accurately predicting crop survival and yield under future climate change. Here, we investigated the impacts of heat wave and drought on cherry tomato seedlings (Solanum lycopersicum L.) grown in growth chambers as well as the subsequent recovery from the combined stress. Seedlings were exposed to well watered and drought treatments under ambient temperature (i.e. 26 °C), until half of them were imposed by a 7-day 42 °C heat wave. The droughted seedlings were then rehydrated upon the relief of the heat wave treatment. Leaf gas exchange, plant growth, leaf water relations and chlorophyll content were measured during the experimental period.

Results/Conclusions The 7-day heat wave reduced leaf gas exchange rates, plant growth and chlorophyll content, while it had no impacts on leaf water relations. By contrast, drought stress led to greater reductions in leaf gas exchange rates, growth and water relations than heat wave. More interestingly, the growth and chlorophyll content were lower in the combined heat-drought stress than single drought stress, indicating that the negative impacts of drought on plants were exacerbated by heat wave. After rehydration, leaf water potentials exhibited rapid recovery, while the recovery of leaf gas exchange from drought was largely lagged, to a greater extent in the heat-drought combination than single drought stress treatment. Our results show that heat wave in combination with drought stress will impose greater negative impacts on cherry tomato seedlings than single stress factor. Heat wave treatment can significantly delay plant recovery from drought stress. Thus, our study highlights that the interactive effects of drought and heat wave need to be fully considered in the crop management under future climates.