Numerical simulation of new multiple layer plant canopy model: Application to the soil-plant-atmosphere system

In order to investigate the quantitative exchange of energy or vapor between soil and plants or between plants and the atmosphere for a plant community in a closed system, the multiple layer plant canopy model developed from NEO-SPAM (Kanda et al., 1990) was tested. The plant system was described as a dynamic model, which combined the time-dependent diffusion-type equation expressing water uptake through plants with the energy budget equation for the leaves. Similar to the multilayer energy budget model, the plant canopy was divided into layers and the converted difference equations were solved. Instead of leaf conductance, the water vapor diffusion coefficient (k(e)) was used to characterize the transpiration. The corresponding opening rate of stoma was described using a multiplicative environmental function model (Jarvis, 1976), while the atmosphere system was calculated according to the K-theory. k(e) decreased along a saturation-type curve as the air specific humidity difference (delta(e)) increased, independent of the other environmental factors. When the air temperature was increased while keeping other environmental factors constant, the transpiration rate through the plant canopy varied according to a 1-peak curve. The transpiration characteristic from the plant canopy against delta(e) and leaf temperature acted as a feedback response of the plant-atmosphere interaction. The calculated results regressed well with the measured transpiration rate from the water cultured plant community (Vinca rosea) set in the greenhouse.