Short-Term Temperature Response of Leaf Respiration in Different Subtropical Urban Tree Species

Abstract

Plant leaf respiration is one of the critical components of the carbon cycle in terrestrial ecosystems. To predict changes of carbon emissions from leaves to the atmosphere under a warming climate, it is, therefore, important to understand the thermodynamics of the temperature response of leaf respiration. In this study, we measured the short-term temperature response of leaf respiration from five different urban tree species in a subtropical region of southern China. We applied two models, including an empirical model (the Kavanau model) and a mechanistic model (Macromolecular Rate Theory, MMRT), to investigate the thermodynamic properties in different plant species. Both models are equivalent in fitting measurements of the temperature response of leaf respiration with no significant difference (p = 0.67) in model efficiency, while MMRT provides an easy way to determine the thermodynamic properties, i.e., enthalpy, entropy, and Gibbs free energy of activation, for plant respiration. We found a conserved temperature response in the five studied plant species, showing no difference in thermodynamic properties and the relative temperature sensitivity for different species at low temperatures (<42°C). However, divergent temperature response among species happened at high temperatures over 42°C, showing more than two-fold differences in relative respiration rate compared to that below 42°C, although the causes of the divergent temperature response remain unclear. Notably, the convergent temperature response at low temperatures could provide useful information for land surface models to improve predictions of climate change effects on plant respiration.

Keywords: Gibbs free energy of activation; Leaf respiration; enthalpy; entropy; macromolecular rate theory; temperature response; temperature sensitivity.

FIGURE 1

Temperature response of leaf respiration under different scales of x-axis. (A) The non-linearity of the Arrhenius plot using the logarithm of leaf respiration rate (lnR) of F. virens (black circles) plotted against 1/T with temperature expressed in Kelvins. The black and red lines show model fits to the measurements using the Kavanau model and MMRT, respectively. (B) The linearisation of the temperature response curve using the same data from panel (A), but the x-axis was changed from 1/T to 1/(T-T₀), where T₀ = 268.8 K.

FIGURE 2

Temperature response measurements (black circles) of leaf respiration over five different urban tree species, including F. virens (circles, A–D), F. altissima (squares, E–I), M. alba (triangles, J–N), E. apiculatus (diamonds, O–S), and C. burmannii (pentagrams, T–W). Each curve (23 curves in total) was fitted by the Kavanau model (black line) and MMRT (red line). The last panel gives a comparison of Nash and Sutcliffe model efficiency (NSE) between the Kavanau model and MMRT for 23 the individual temperature response curves.

FIGURE 3

Temperature dependence of thermodynamic properties (ΔH^‡, ΔS^‡, and ΔG^‡) of leaf respiration from F. virens. (A) The temperature dependences of ΔG^‡ that is determined by the absolute rate function Eq. 2 based on the measurements. Both the Kavanau (black line) and MMRT (red lin e) can predict the change of ΔG^‡. (B) Temperature dependence of ΔH^‡ and ΔS^‡ from MMRT, assuming the temperature independence of ΔCp^‡ as a constant.

FIGURE 4

Temperature response of leaf respiration of five urban tree species. (A) Demonstrated the mean short-term temperature response measurements on a linear scale. (B) Demonstrated the normalized temperature response curves for five different species. The rates were normalized to the rates at 25°C of each species. (C) Showed the normalized rates at a log-scale. The mean respiration rates were calculated where at least two measurements (two replicates) were available at each temperature for each species.