Transpiration and photosynthesis are two closely related and intercoupled processes that dominate the physiological activities and yield of crops. Therefore, there is a need to study water-carbon coupling modeling at various scales to increase water use efficiency (WUE). Using a summer maize field in North China as an example, the variations in leaf and canopy photosynthesis and transpiration (or evapotranspiration) were analyzed. The synthetic model of photosynthesis-transpiration based on stomatal behavior (SMPT-SB) was then calibrated and validated at the two scales. The leaf photosynthesis and transpiration, as well as the canopy photosynthesis and evapotranspiration, have a consistent diurnal trend. However, the canopy evapotranspiration is affected more by topsoil moisture content. The regression coefficient between leaf photosynthesis, transpiration, and WUE estimated by the SMPT-SB and the measured values was found to approach 1, with a coefficient of determination of more than 0.74. The relative error between the two sets of values is less than 11%. Therefore, the SMPT-SB could express fairly well leaf photosynthesis, transpiration, and WUE. The estimated canopy-scale photosynthesis by the SMPT-SB is also in good agreement with the measured values. However, this model underestimates the canopy evapotranspiration when the topsoil has high moisture content and therefore overestimates, to a certain extent, the canopy WUE.
Canopy resistance estimation model based on the scaling-up leaf stomatal resistance is the focus of evapotrantion research, as there is a need to select the proper scaling-up model for winter wheat in typical areas of North China. Two years of field experimental data are used for the Leuning-Ball and Jarvis stomatal model calibration and validation, canopy resistance estimation models are established based on Leuning-Ball and Jarvis stomatal models, their application effects are compared and verified. Results show that daily variation of stomatal resistance of winter wheat is higher than that of canopy resistance, and there exists scale differences between leaf and canopy scale; Leuning-Ball stomatal model can be better explicated by the response of stomatal conductance towards environmental factors; Leuning-Ball canopy resistance estimation models turn out to be an effective canopy resistance simulation, and thus can be applied to research on the scaling-up of vapor transmission resistance of winter wheat in typical areas of North China.
