Wheat respiratory O-2 consumption falls with night warming alongside greater respiratory CO2 loss and reduced biomass

Warming nights are correlated with declining wheat growth and yield. As a key determinant of plant biomass, respiration consumes O-2 as it produces ATP and releases CO2 and is typically reduced under warming to maintain metabolic efficiency. We compared the response of respiratory O-2 and CO2 flux to multiple night and day warming treatments in wheat leaves and roots, using one commercial (Mace) and one breeding cultivar grown in controlled environments. We also examined the effect of night warming and a day heatwave on the capacity of the ATP-uncoupled alternative oxidase (AOX) pathway. Under warm nights, plant biomass fell, respiratory CO2 release measured at a common temperature was unchanged (indicating higher rates of CO2 release at prevailing growth temperature), respiratory O-2 consumption at a common temperature declined, and AOX pathway capacity increased. The uncoupling of CO2 and O-2 exchange and enhanced AOX pathway capacity suggest a reduction in plant energy demand under warm nights (lower O-2 consumption), alongside higher rates of CO2 release under prevailing growth temperature (due to a lack of down-regulation of respiratory CO2 release). Less efficient ATP synthesis, teamed with sustained CO2 flux, could thus be driving observed biomass declines under warm nights. Elevated night growth temperature drove acclimation of wheat respiratory O(2)consumption, but not respiratory CO(2)release. Night warming also reduced biomass and enhanced the capacity of the alternative oxidase pathway.