Is there a universal temperature dependence of plant metabolism?

Abstract:

Metabolic theory (MT) hypothesizes that the kinetics of plant metabolism, from cells to ecosystems, are characterized by an exponential Arrhenius relationship with an activation energy E = 0.32 eV corresponding to net photosynthesis. This estimate of E was obtained using the Farquhar-von Caemmerer-Berry (FvCB) model for Rubisco-limited C₃ photosynthesis, parameterized for a single species of transgenic tobacco. While the numeric value has become canon, and even suggested to be a 'universal temperature dependence' of plant metabolism, it has surprisingly never been evaluated for photosynthesis in diverse taxa. Additionally, most estimates of E at higher levels of organization (individuals, communities, and ecosystems) have varied significantly from 0.32 eV. Here we assess whether 0.32 eV characterizes a universal temperature dependence of plant metabolism. We use new and published assimilation-temperature (A-T) curves, which is the largest such data set compiled to date. Our A-T data comprise two types. First, we parameterized the FvCB model using V_cmax and J_max kinetics data to produce 604 modelled A-T curves for 83 species. Second, we use 484 empirical A-T curves for 123 species. For both types of data, activation energies were estimated using Sharpe-Schoolfield model fits to A-T data. Results showed that mean, median, and global abundance-weighted estimates of E were all significantly greater than the canonical 0.32 eV. These new estimates of E did not differ significantly from 0.65 eV, an approximate average for biochemical reactions of respiration that is widely applied in MT. Additionally, new estimates of E varied widely across taxa. Thus, while the new estimate of E for photosynthesis is significantly greater than 0.32, there is wide variation around the new estimate, so it should be viewed as only a general (and not universal) temperature dependence within MT.