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 Rlight . We investigated whether responses of Rlight to short- and long-term changes in leaf temperature depend on the technique used to estimate Rlight . We grew Eucalyptus tereticornis in whole-tree chambers under ambient temperature (AT) or AT + 3°C (elevated temperature, ET). We assessed dark respiration Rdark and light respiration with the Kok (RKok ) and Laisk (RLaisk ) 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 Rdark , RKok or RLaisk . Although the thermal sensitivities of RKok or RLaisk were similar, RKok was higher than RLaisk . We found negative values of RLaisk at the lowest measurement temperatures, indicating positive net CO2 uptake, which we propose may be related to phosphoenolpyruvate carboxylase activity. Light suppression of Rdark 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 Rlight or light suppression of Rdark between 20 and 35°C. Negative rates of RLaisk imply that this method may become less reliable at low temperatures.