Dynamic responses of gas exchange and photochemistry to heat interference during drought in wheat and sorghum

Drought and heat stress significantly affect crop growth and productivity worldwide. It is unknown how heat interference during drought affects physiological processes dynamically in crops. Here we focussed on gas exchange and photochemistry in wheat and sorghum in response to simulated heat interference via +15°C of temperature during ~2 week drought and re-watering. Results showed that drought decreased net photosynthesis (Anet), stomatal conductance (gs), maximum velocity of ribulose-1, 5-bisphosphate carboxylase/oxygenase carboxylation (Vcmax) and electron transport rate (J) in both wheat and sorghum. Heat interference did not further reduce Anet or gs. Drought increased non-photochemical quenching (Φnpq), whereas heat interference decreased Φnpq. The δ13C of leaf, stem and roots was higher in drought-treated wheat but lower in drought-treated sorghum. The results suggest that (1) even under drought conditions wheat and sorghum increased or maintained gs for transpirational cooling to alleviate negative effects by heat interference; (2) non-photochemical quenching responded differently to drought and heat stress; (3) wheat and sorghum responded in opposing patterns in δ13C. These findings point to the importance of stomatal regulation under heat crossed with drought stress and could provide useful information on development of better strategies to secure crop production for future climate change.