Drought increases heat tolerance of leaf respiration in Eucalyptus globulus saplings grown under both ambient and elevated atmospheric [CO(2)] and temperature

Climate change is resulting in increasing atmospheric [CO(2)], rising growth temperature (T), and greater frequency/severity of drought, with each factor having the potential to alter the respiratory metabolism of leaves. Here, the effects of elevated atmospheric [CO(2)], sustained warming, and drought on leaf dark respiration (R (dark)), and the short-term T response of R (dark) were examined in Eucalyptus globulus. Comparisons were made using seedlings grown under different [CO(2)], T, and drought treatments. Using high resolution T–response curves of R (dark) measured over the 15–65 °C range, it was found that elevated [CO(2)], elevated growth T, and drought had little effect on rates of R (dark) measured at T <35 °C and that there was no interactive effect of [CO(2)], growth T, and drought on T response of R (dark). However, drought increased R (dark) at high leaf T typical of heatwave events (35–45 °C), and increased the measuring T at which maximal rates of R (dark) occurred (T (max)) by 8 °C (from 52 °C in well-watered plants to 60 °C in drought-treated plants). Leaf starch and soluble sugars decreased under drought and elevated growth T, respectively, but no effect was found under elevated [CO(2)]. Elevated [CO(2)] increased the Q (10) of R (dark) (i.e. proportional rise in R (dark) per 10 °C) over the 15–35 °C range, while drought increased Q (10) values between 35 °C and 45 °C. Collectively, the study highlights the dynamic nature of the T dependence of R (dark) in plants experiencing future climate change scenarios, particularly with respect to drought and elevated [CO(2)].