Thermodynamic insights into thermal acclimation of leaf dark respiration in two subtropical species: comparative analysis of MMRT and GTD models

Background Leaf dark respiration (Rd) responds to short-term temperatures and acclimates to changes in long-term temperatures. Although accurate Rd-temperature (Rd-T) models are crucial for carbon flux prediction in forest ecosystems, two thermodynamically grounded frameworks—the macromolecular rate theory (MMRT) and the general temperature dependence (GTD) model—have not been compared. Moreover, these models can uniquely link molecular processes to leaf-scale Rd, providing mechanistic interpretations of thermal acclimation that empirical models cannot achieve. Methods Here, we grew two common subtropical species, Cyclobalanopsis glauc and Schima superba, in artificial climatic chambers under three temperature treatments (daytime/nighttime = 30/25°C, 25/20°C, and 20/15°C). After 15 days of temperature treatment, Rd-T response curves were measured at night. Key Results Despite both models showed equivalent predictive power (R², AICc, RMSE), MMRT was prioritized for its detailed mechanistic interpretation, which links the molecular conformation to temperature-dependent leaf Rd via temperature-dependent changes in heat capacity (ΔC). Although both species employ type II thermal acclimation, the thermal acclimation strategies differ: for C. glauca, the increase in ΔC under warming suggests a shift toward enhanced enzyme conformational flexibility, achieving partial homeostasis. In contrast, S. superba exhibited overcompensation without changes in ΔC or activation enthalpy (ΔH), indicating a strategy governed by factors independent of these thermodynamic parameters. Conclusions In our study, the MMRT model is recommended to fit Rd-T response curves, and ΔC serves as a bridge between thermodynamic principles and species-specific thermal acclimation mechanisms, successfully distinguishing the strategy of C. glauca (associated with changing enzyme thermodynamics) from that of S. superba (independent of such thermodynamic adjustments).