2004 Volume 17 Issue 3 Pages 274-294
Impacts of the change of LAI on transpiration and net photosynthesis of a single leaf and evapotranspiration (ET), net photosynthesis (CER) and water use efficiency (WUEET=CER ⁄ ET) of a whole canopy were evaluated at four growing stages of rice in a paddy field by the multilayer model. LAI was changed by multiplying the present vertical profile of leaf area density by 0.0 to 2.2, which coincides with LAI of 0 to 10 approximately. As the increase of LAI, ET and CER increased asymptotically, reached their maximum and decreased for more excessive LAI. This is because, as the increase of LAI, transpiration and net photosynthesis in the upper canopy layers increased asymptotically and decreased in the middle and lower layers and evaporation from water or soil beneath the canopy decreased asymptotically. These changes of ET and CER caused WUEET to increase asymptotically and reach its maximum. The maximum of ET, CER and WUEET or the optimum LAI for CER and WUEET tended to occur more easily at earlier or later hours in the daytime or under lower light condition. This is because solar radiation and PAR in the lower canopy layers decreased to less level by more mutual shading as LAI increased in these conditions. The optimum LAI for CER and WUEET on the four days were in the range of 5.0 to 10.0 and 5.8 to 10.0 respectively, which were different for crop stage, time and meteorological conditions. The optimum LAI for CER was little higher than those of other researches owing mainly to weather condition of higher solar radiation on the four days.
