School of Science, The University of Waikato, Hamilton, New Zealand.
Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, ACT, Australia.
Glob Chang Biol. 2018 Apr;24(4):1538-1547. doi: 10.1111/gcb.13936. Epub 2017 Nov 14.
Temperature is a crucial factor in determining the rates of ecosystem processes, for example, leaf respiration (R) - the flux of plant respired CO from leaves to the atmosphere. Generally, R increases exponentially with temperature and formulations such as the Arrhenius equation are widely used in earth system models. However, experimental observations have shown a consequential and consistent departure from an exponential increase in R. What are the principles that underlie these observed patterns? Here, we demonstrate that macromolecular rate theory (MMRT), based on transition state theory (TST) for enzyme-catalyzed kinetics, provides a thermodynamic explanation for the observed departure and the convergent temperature response of R using a global database. Three meaningful parameters emerge from MMRT analysis: the temperature at which the rate of respiration would theoretically reach a maximum (the optimum temperature, T ), the temperature at which the respiration rate is most sensitive to changes in temperature (the inflection temperature, T ) and the overall curvature of the log(rate) versus temperature plot (the change in heat capacity for the system, ΔCP‡). On average, the highest potential enzyme-catalyzed rates of respiratory enzymes for R are predicted to occur at 67.0 ± 1.2°C and the maximum temperature sensitivity at 41.4 ± 0.7°C from MMRT. The average curvature (average negative ΔCP‡) was -1.2 ± 0.1 kJ mol K . Interestingly, T , T and ΔCP‡ appear insignificantly different across biomes and plant functional types, suggesting that thermal response of respiratory enzymes in leaves could be conserved. The derived parameters from MMRT can serve as thermal traits for plant leaves that represent the collective temperature response of metabolic respiratory enzymes and could be useful to understand regulations of R under a warmer climate. MMRT extends the classic TST to enzyme-catalyzed reactions and provides an accurate and mechanistic model for the short-term temperature response of R around the globe.
温度是决定生态系统过程速率的关键因素，例如，叶呼吸（R）——植物从叶片向大气释放的 CO 的通量。一般来说，R 随温度呈指数增长，阿伦尼乌斯方程等公式广泛应用于地球系统模型中。然而，实验观察表明，R 的增长与指数增长存在显著且一致的偏离。这些观察到的模式背后的原理是什么？在这里，我们利用全球数据库证明，基于酶促动力学的过渡态理论（TST）的大分子速率理论（MMRT），为观察到的偏离以及 R 的收敛温度响应提供了热力学解释。MMRT 分析产生了三个有意义的参数：呼吸理论上达到最大速率的温度（最适温度 T）、呼吸速率对温度变化最敏感的温度（转折温度 T）以及 log（速率）与温度关系图的整体曲率（系统的热容变化，ΔCP‡）。平均而言，MMRT 预测 R 的呼吸酶的最高潜在酶促速率预计在 67.0±1.2°C 发生，最大温度敏感性在 41.4±0.7°C 发生。平均曲率（平均负 ΔCP‡）为-1.2±0.1 kJ mol K。有趣的是，T、T 和 ΔCP‡在生物群区和植物功能类型之间没有明显差异，这表明叶片呼吸酶的热响应可能是保守的。MMRT 从衍生的参数可以作为叶片的热特性，代表代谢呼吸酶的集体温度响应，对于了解在温暖气候下 R 的调控可能是有用的。MMRT 将经典的 TST 扩展到酶促反应，并为全球范围内 R 的短期温度响应提供了准确和机制模型。
