Temperature responses of leaf respiration in light and darkness are similar and modulated by leaf development

Abstract

In the context of global warming, temperature responses of leaf respiration (R) in light and darkness (RL and RDk) are essential to models of global carbon dynamics. Many models rely on constant thermal sensitivity (characterized by Q10) of leaf respiration. However, it remains unclear whether Q10 is similar for RL and RDk, given the differences in the rate and pathways of respiration between light and dark. Warm season growth causes thermal acclimation of R, and leaf development stage also affects R. It is uncertain if these factors influence the temperature response of R, which hinders the development of respiration models. Uncertainty in temperature responses of RL can also be associated with methodology. Recently, the Kok method has been improved by combining chlorophyll fluorescence and gas exchange to estimate RL. These advances have improved the accuracy of RL estimates. In this study, we developed a new method, the Kok-iterCc method. Using three methods (the Kok, Yin and Kok-iterCc methods), we measured the temperature response of RL and RDk in leaves of different leaf development stages (immature and mature) of two evergreen tree species (Castanopsis carlesii and Ormosia henryi) in two seasons (winter and summer). Q10 and basal respiration rate (R25) were then calculated. We found that, 1) When estimated by the Yin and Kok-iterCc methods, RL and RDk had similar Q10 (c. 2.5). The Kok method overestimated both Q10 and light inhibition of R. RL/RDk was not influenced by leaf temperature. 2) Acclimation of R in summer was associated with a decrease in R25 but not in Q10 in both species, which was related to changes in leaf nitrogen content between seasons. 3) Leaf development significantly affected R25 and Q10. Importantly, Q10 of RL and RDk was 40% higher in mature leaves than in immature leaves. The difference in contributions of growth and maintenance components of respiration are likely the main reason for the lower Q10 of growing leaves compared with mature leaves. Our results suggest that similar Q10 can be used to model RL and RDk, while leaf development related changes in Q10 require special consideration in future respiration models.