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

Peatlands contain 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.

泥炭地储存了全球三分之一的土壤碳（C），但目前学界对泥炭地生态系统响应长期增温的机制尚缺乏系统认知。本研究通过整合变化环境下云杉与泥炭地响应（SPRUCE）试验站点的长期增温观测数据，对过程导向模型——陆地生态系统（TECO）模型进行参数约束，以系统解析增温对泥炭地生态系统碳通量的影响效应。模型模拟结果表明，生态系统尺度的光合作用与自养呼吸存在显著的热适应（thermal acclimation）现象，其温度敏感性随增温程度呈线性下降趋势。采用经热适应调整的参数值开展模拟，得到的总初级生产力（Gross Primary Production, GPP）、净初级生产力（Net Primary Production, NPP）以及植物自养呼吸（plant autotrophic respiration, Ra）的模拟结果，均低于使用未考虑热适应的参数值得到的模拟结果。相较之下，采用热适应参数值模拟得到的生态系统呼吸（ecosystem respiration, ER）则高于未考虑热适应参数值的模拟结果。净生态系统CO₂交换（Net Ecosystem CO₂ Exchange, NEE）在采用增温处理组的观测数据约束模型参数后，模拟结果显著升高，碳释放速率达28.3 g C m⁻² yr⁻¹ °C⁻¹。本项数据-模型整合研究表明，泥炭地的碳释放量大概率高于此前的学界预估。若地球系统模型未纳入植物的生理热适应（physiological thermal acclimation）过程，则可能高估增温背景下泥炭地的碳固持能力。因此，在模型中纳入植物的长期生理热适应过程，对于更精准预测未来气候背景下的全球碳动态及其对气候变化的反馈效应，具有至关重要的意义。