Responses of respiration in the light to warming in field-grown trees: a comparison of the thermal sensitivity of the Kok and Laisk methods

The Kok and Laisk techniques can both be used to estimate light respiration R _light . We investigated whether responses of R _light to short- and long-term changes in leaf temperature depend on the technique used to estimate R _light . We grew Eucalyptus tereticornis in whole-tree chambers under ambient temperature (AT) or AT + 3°C (elevated temperature, ET). We assessed dark respiration R _dark and light respiration with the Kok (R _Kok ) and Laisk (R _Laisk ) methods at four temperatures to determine the degree of light suppression of respiration using both methods in AT and ET trees. The ET treatment had little impact on R _dark , R _Kok or R _Laisk . Although the thermal sensitivities of R _Kok or R _Laisk were similar, R _Kok was higher than R _Laisk . We found negative values of R _Laisk at the lowest measurement temperatures, indicating positive net CO ₂ uptake, which we propose may be related to phosphoenolpyruvate carboxylase activity. Light suppression of R _dark decreased with increasing leaf temperature, but the degree of suppression depended on the method used. The Kok and Laisk methods do not generate the same estimates of R _light or light suppression of R _dark between 20 and 35°C. Negative rates of R _Laisk imply that this method may become less reliable at low temperatures.