Impacts of drought on leaf respiration in darkness and light in Eucalyptus saligna exposed to industrial-age atmospheric CO2 and growth temperature

P>Our study assessed the impact of a wide range of industrial-age climate scenarios on leaf respiration (R) in Eucalyptus saligna. Well-watered or sustained drought-treated plants were grown in glasshouses differing in atmospheric CO2 concentration ([CO2]) (280, 400 and 640 mu l l-1) and temperature (26 and 30 degrees C). Rates of R in darkness (R-dark) and light (R-light), photosynthesis (A) and related leaf traits (mass : area relationships, and nitrogen, phosphorus, starch and sugar concentrations) were measured. Light inhibited R in all cases (R-light < R-dark) (well-watered: 40%; drought-treated: 73%). Growth [CO2] and temperature had little impact on area-based rates of R-dark or R-light, with R-light exhibiting minimal thermal acclimation. By contrast, sustained drought resulted in reduced R-dark, R-light and A, with the inhibitory effect of drought on A and R-light (c. 50-70%) greater than that on R-dark (c. 15%). Drought effects were fully reversible after watering. Variability in R-light appeared to be dependent on the underlying rate of R-dark and associated Rubisco activity. Collectively, our data suggest that there is an asynchronous response of leaf carbon metabolism to drought, and a tighter coupling between R-light and A than between R-dark and A, under both past and future climate scenarios. These findings have important implications for ecosystem/global models seeking to predict carbon cycling.