Drought exerts a greater influence than growth temperature on the temperature response of leaf day respiration in wheat (Triticum aestivum)

We assessed how the temperature response of leaf day respiration (Rd) in wheat responded to contrasting water regimes and growth temperatures. In Experiment 1, well-watered and drought-stressed conditions were imposed on two genotypes; in Experiment 2, the two water regimes combined with high (HT), medium (MT) and low (LT) growth temperatures were imposed on one of the genotypes. Rd was estimated from simultaneous gas exchange and chlorophyll fluorescence measurements at six leaf temperatures (Tleaf) for each treatment, using the Yin method for non-photorespiratory conditions and the non-rectangular hyperbolic fitting method for photorespiratory conditions. The two genotypes responded similarly to growth and measurement conditions. Estimates of Rd for non-photorespiratory conditions were generally higher than those for photorespiratory conditions but their responses to Tleaf were similar. Under well-watered conditions, Rd and its sensitivity to Tleaf slightly acclimated to LT but did not acclimate to HT. Temperature sensitivities of Rd were considerably suppressed by drought, and the suppression varied among growth temperatures. Thus, it is necessary to quantify interactions between drought and growth temperature for reliably modelling Rd under climate change. Our study also demonstrated that the Kok method, a currently popular method for estimating Rd, underestimated Rd significantly and should be abandoned. HighlightLeaf day respiration (Rd) acclimated little to growth temperature, but significantly to drought by reducing its thermal sensitivity. The Kok method underestimates Rd and should no longer be used.