用光合-蒸散耦合模型模拟冬小麦CO2通量的日变化

根据 SPAC理论建立了一个冬小麦光合和蒸散的耦合模型。冬小麦 CO2 通量包括冠层光合、呼吸和土壤呼吸。冠层光合采用了 Farquhar光合作用生化模型 ,并通过冠层阻力的参数化将光合作用与蒸腾作用耦合起来。用涡度相关方法观测了 CO2通量 ,对模型进行了验证 ,结果显示模型可以较好地模拟 CO2 通量日变化过程。对模型的敏感性分析发现日间 CO2 通量最敏感的参数是初始量子效率。其次 ,CO2 通量对光响应曲线凸度、CO2 补偿点、凋萎点和叶面积指数的变化也有着较强的敏感性 ;夜间 CO2 通量敏感的参数是最适温度下 Rubisco催化能力和暗呼吸参数

Modeling diurnal variations of CO2 flux over winter wheat with a coupled model of photosynthesis and evapotranspiration

A coupled photosynthesis-evapotranspiration model over winter wheat was developed according to the theory based on SPAC. The model consists of three submodels, i.e., a canopy evapotranspiration model, a canopy photosynthesis model and a model of water and heat transfer in soil. The canopy evapotranspiration model comprises a solar radiation transfer sub-model, a heat radiation sub-model, an energy balance sub-model and a canopy resistance sub-model. The canopy photosynthesis model comprises a leaf photosynthesis sub-model, a stomatal conductance sub-model and a leaf water potential sub-model. The water and heat transfer model in soil comprises a water movement in soil sub-model, a water absorption sub-model for root and a heat diffusion equation sub-model. The three models were coupled by calling the canopy photosynthesis model to calculate canopy resistance in the canopy evapotranspiration model, calling the evapotranspiration model to obtain soil temperature and canopy temperature to calculate photosynthesis rate, soil respiration etc. At the same time, the canopy evapotranspiration model combined with the water and the model of heat transfer in the soil to solve energy balance equation and calculate soil resistance. Modular structure is used in the model and every model could be substituted by more advanced module. The time step of the model is one hour at most.The biochemical model proposed by Farquhar was used to calculate canopy photosynthesis. The modeling of Photosynthesis and that of evapotranspiration are coupled in modeling by parameterization of canopy resistance.The performance of the model was evaluated with data measured by the eddy covariance method, the results showed that the model could simulate diurnal variations of CO_2 flux very well. The sensitivity of the model to changes in values of the main parameters was analyzed. In daytime the most sensitive parameter of CO_2 flux is found to be the initial quantum efficiency in daytime and CO_2 flux is sensitive to changes in the convexity of photosynthesis-light response curve, CO_2 compensation point, the wilting point and leaf area index. In the nighttime, parameters which photosynthesis was sensitive to were the Rubisco catalytic capacity at optimal temperature and the dark respiration parameter.