The Dynamic Simulation of Photosynthesis in Apple Tree Canopy

Coupled model of canopy photosynthesis (Pn) and stomatal conductance (Gs) was presented. This model could simulate the response of Pn to microclimatic factors and the diurnal courses of Pn. The influences of the microclimatic factors on photosynthesis were different. There were strong interactions among the various microclimatic factors. The results showed that photosynthesis was mainly driven by the net radiation and CO2 concentration. Since CO2 concentration in the existing environment remained relatively stable, the net radiation became the major driving factor of photosynthesis. From this model, we can see that only one peak appeared in the diurnal courses of photosynthesis, and this photosynthetic peak reached at midday. These established models were tested by the observation data in an apple (Malus pumila Mill. 'Fuji') orchard (latitude 40°13' north, longitude 116°13'east, altitude 79 m). On the basis of this model, we predicted that during a whole day an apple tree with leaf area of 37.95 m2 would fix 420-560 g of CO2 on clear days, and fix 120-200 g of CO2 on cloudy days. There was a satisfactory correspondence between measured and simulated values of Pn with observation data in the apple orchard.