Contrusting Physiological Properties Of Shaded And Sunlit Leaves, And Applying A Photosynthesis Model For Cotton

The energy exchange, evapotranspiration, and carbon exchange by plant canopies depend on leaf stomatal control. The treatment of this control has been required by land components of climate and carbon models. Physiological models can be used to simulate the responses of stomatal conductance to changes in atmospheric and soil environments. Big-leaf models that treat a canopy as a single leaf tend to overestimate fluxes of CO₂ and water vapor. Models that differentiate between sunlit and shaded leaves largely overcome these problems.To prove this, a multi-layered, two-leaf model based on observed data of cotton for photosynthesis, stomatal conductance, transpiration, and energy fluxes is presented in this paper. It includes: (1) Under different radiation environment, physiological properties of sunlit and shaded leaves, such as photosynthesis, stomatal conductance, transpiration, and radiation absorption are contrasted. We also give the spatio-temporal change of these properties to visually testify the necessity of treating sunlit and shaded leaves separately. (2) a photosynthesis-stomatal conductance model for sunlit and shaded leaves separately, and it scales up from leaf to canopy. The calculation of photosynthesis shows the value of big-leaf model is totally 13% higher than that of two-leaf model. So, the contribution of carbon sink is magnified in estimating photosynthesis by big-leaf model in carbon exchanges between the biosphere and atmosphere.