Thermal acclimation impacts on global carbon dynamics

Background/Question/Methods

To simulate the climate feedbacks among the terrestrial ecosystems and atmosphere, modelers have dedicated to incorporate as many biogeochemical or biophysical processes into models as what can be exacted from the empirical or theoretical evidences. Some major components of an ecosystem model, such as, photosynthesis and respiration processes, are determinant to the model structure and critical for simulating ecosystem dynamics; therefore any potential misinterpretation of these processes would inevitably result in misunderstandings in model simulations and projections. Recently observed empirical evidences of “delayed” plant/ ecosystem responses to climate warming posed a risk to credibility of ecosystem estimations using models, either at regional or global scale, without considering the “plasticity” of model coupled processes. The phenomenon of delayed responses is intrinsically caused by the ecosystem “thermal acclimation”, which mainly occurred in the photosynthesis (PT), autotrophic respiration (RA) and heterotrophic respiration (RH) processes. To assess potential impacts of thermal acclimation on carbon dynamics, we applied a process-based biogeochemical model, the Terrestrial Ecosystem Model (TEM) to global scale terrestrial ecosystems. TEM was modified and incorporated recently designed dynamic algorithms to simulate corresponding thermal acclimation of PT, RA and RH.

Results/Conclusions

Carbon fluxes of gross primary production (GPP), net primary production (NPP) and net ecosystem production (NEP) were simulated and examined for 12 plant function types at a monthly time step, under both historical (1900-2000) and future (2001-2100) climate scenarios. Generally, under historical climate conditions, NPP and NEP were not significantly affected by thermal acclimation of either processes; GPP was slightly higher when accounting for RA process. Under future warming climate without including thermal acclimation, TEM predicted abrupt increase before 2050 and fast decline after 2050 for both GPP and NPP; NEP was projected to decrease continuously in the 21 century, to about -10 Pg C in the 2090s. From the perspective of global carbon dynamics, by incorporating the thermal acclimation into TEM, GPP would keep increasing in the whole 21 century, only with lower rate after 2050, approach about 130 Pg C in the 2090s; NPP, however would first increase and then decrease after 2050, but at a much lower rate than original TEM predicted; NEP would decrease due to increased ecosystem respiration under warmer climate, but at a low rate, and reach about -1 Pg C in the 2090s. Thermal acclimation should be cautiously incorporated in ecosystem models to simulate carbon dynamics under warming climate.