Thermal acclimation of plant photosynthesis and autotrophic respiration in a northern peatland

Abstract

Peatland contains one-third of global soil carbon (C), but the responses of peatland ecosystems to long-term warming are not well understood. Here, we pursue an emergent understanding of warming effects on ecosystem C fluxes at peatlands by constraining a process-oriented model, the Terrestrial ECOsystem (TECO) model, with observational data from a long-term warming experiment at the Spruce and Peatland Responses Under Changing Environments (SPRUCE) site. Model-based assessments show that ecosystem-level photosynthesis and autotrophic respiration exhibited significant thermal acclimation, with temperature sensitivities being linearly decreased with warming. Using the thermal-acclimated parameter values, simulated gross primary production (GPP), net primary production (NPP), and plant autotrophic respiration (Ra), were all lower than those simulated with non-thermal acclimated parameter values. In contrast, ecosystem respiration (ER) simulated with thermal acclimated parameter values was higher than that simulated with non-thermal acclimated parameter values. Net ecosystem CO2 exchange (NEE) was much higher after constraining model parameters with observational data from the warming treatments, releasing C at a rate of 28.3 g C m-2 yr-1 °C-1. Our data-model integration study suggests that peatlands are likely to release more C than previously estimated. Earth system models may overestimate C uptake by peatlands under warming if physiological thermal acclimation of plants is not incorporated. Thus, it is critical to consider the long-term physiological thermal acclimation of plants in the models to better predict global C dynamics under future climate and their feedback to climate change.