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 (day/night 30/25, 25/20 and 20/15 °C). After 15 d of temperature treatment, Rd-T response curves were measured at night. KEY RESULTS: Despite both models showing 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, their 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: 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).