Wheat respiratory O2 consumption falls with night warming alongside greater respiratory CO2 loss and reduced biomass

Abstract

<p><b>Warming nights are correlated with declining wheat growth and yield. As a key determinant of plant biomass, respiration consumes O₂ as it produces ATP and releases CO₂ and is typically reduced under warming to maintain metabolic efficiency. We compared the response of respiratory O₂ 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 O₂ consumption at a common temperature declined, and AOX pathway capacity increased. The uncoupling of CO₂ and O₂ exchange and enhanced AOX pathway capacity suggest a reduction in plant energy demand under warm nights (lower O₂ 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.</b></p>