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

In the context of global warming, temperature responses of leaf respiration (R) in light and darkness (R_L and R_Dk) 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 R_L and R_Dk, 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 R_L can also be associated with methodology. Recently, the Kok method has been improved by combining chlorophyll fluorescence and gas exchange to estimate R_L. These advances have improved the accuracy of R_L estimates.

In this study, we developed a new method, the Kok-iterC_c method. Using three methods (the Kok, Yin and Kok-iterC_c methods), we measured the temperature response of R_L and R_Dk 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, R_L and R_Dk had similar Q₁₀ (c. 2.5). The Kok method overestimated both Q₁₀ and light inhibition of R. R_L/R_Dk 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 R_L and R_Dk 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 R_L and R_Dk, while leaf development related changes in Q₁₀ require special consideration in future respiration models.