Role of canopy temperature depression in rice

Abstract

Canopy temperature depression (CTD), the difference between canopy temperature (CT) and air temperature, is induced by evaporative cooling of the plants when stomata open and transpiration takes place. This review describes that CTD in rice is closely associated with stomatal conductance, and they are both affected by the environmental condition and show similar genotypic variation. It then discusses the importance of lowering CT for high yield under heat stress and different water availability conditions. Canopy temperature declines below air temperature with open stomata, and CTD increases (i.e. larger negative value), linearly with increased vapour pressure deficit of the air, with large CTD of −3.0 to −5.0 ​°C not uncommon under drier conditions. While panicle temperature is often 1.0 to 2.0 ​°C higher than leaf temperature, there is sufficient cooling effect that reduces panicle temperature well below air temperature to improve spikelet fertility under hot dry conditions. Large genotypic variation in CTD is commonly found in most studies undertaken, and there are cases where larger CTD has contributed to genotypic heat resistance. The capacity of a genotype to lower CT and to maintain higher stomatal conductance is often associated with the genotype producing higher yield under both well-watered flooded and water deficit conditions. There appears to be good prospect for utilising genotypes with the capacity for large CTD under different growing conditions, and this review concludes with suggestions for ways to hasten rice improvement using CTD as a tool for different growing conditions.