Understanding and quantifying temperature acclimation of plant carbon exchange across multiple plant functional types

Background/Question/Methods

Photosynthesis and respiration on land are the two largest carbon fluxes between the atmosphere and Earth’s surface. The parameterization of these processes represent major uncertainties in the terrestrial component of the Earth System Models (ESMs) used to project future climate change. Research has shown that much of this uncertainty is due to the parameterization of the temperature responses of leaf photosynthesis and autotrophic respiration, which are typically based on short-term empirical responses. Previous work has shown that including longer-term responses to temperature, such as temperature acclimation, can help to reduce this uncertainty and improve model performance. This has been shown to lead to drastic changes in future land-atmosphere carbon feedbacks across multiple models. However, the contemporary formulations available for parameterizing temperature acclimation have many flaws, including an underrepresentation of many important global flora. Here, quantified the short- and long-term temperature responses of maximum Rubisco carboxylation (V_cmax), maximum rate of Ribulos-1,5-bisphosphate regeneration (J_max), and dark respiration (R_d) in multiple species representing each of the major plant functional types (PFTs) used in ESMs. Short-term temperature responses of each process were measured in individuals acclimated for 7 days at one of 5 temperatures (15-35°C). We then quantified variation associated with parameters defining the short-term response that could be account for by acclimation temperature (i.e., the long-term temperature response) as well as individual-specific traits such as leaf nitrogen content and leaf mass per area and, finally, species-speific traits such as leaf phenology (deciduous/evergreen), plant lifespan (annual/perennial), climate of origin (temperate/tropical), and photosynthetic pathway (C₃/C₄). 

Results/Conclusions

Our resulting dataset contained 22 species encompassing each of the major PFTs represented in Earth system models. Our analyses indicated the majority of the variation in the parameters associated with the short-term temperature responses of V_cmax, J_max, and R_d, including their basal rates, could be attributed to the interaction between acclimated temperature and individual- and species-specific traits, revealing that acclimation can influence individual trait relationships in a manner that differs between PFTs. These results suggest that models without acclimation or those using contemporary acclimation formulations (without PFT-specific parameters) are likely incorrectly simulating leaf carbon exchange responses to future warming. As such, we use these data to propose easily incorporable temperature response functions for V_cmax, J_max, and R_d with PFT-specific parameterizations that include acclimation. These functions should significantly improve the functioning of ESMs, resulting in more reliable projections of future carbon-clime feedbacks.