Preliminary Studies on Distribution Law of Photosynthetically Active Radiation in Apricot Canopy and Its Structural Optimization

The 3D PAR(Photosynthetically Active Radiation) distribution in apricot canopies with different ages(2-6 a) were measured to research the variance of Tr(transmittence)with the LAI(Leaf Area Index) by LP-80 AccuPAR.The results showed that the average PAR at different depths in canopy was decreased with the increase of accumulated LAI(Leaf Area Index) by exponential law.In the upper canopy,the Tr(transmittence) was more than the underneath,the decrease of PAR was obvious;In the under-part,the Tr(transmittence) kept slightly lower and without obvious variation.Trend existed in the Tr(transmittence) decreases with the increasing trend of tree ages at same time and weather.But the extinction coefficient varied evidently in different weather and different sunshine angle even in the same canopy.Factors influenced PAR distribution in apricot canopy were various.Complicated correlations also existed among them.Citing an instance of 2-6 a apricot trees,the Tr(transmittence) in middle of the canopy were 49.5%,30.0%,27.5%,13.4% and 7.8% respectively,the Tr(transmittence) under the canopy were29.1%,12.1%,10.9%,6.4% and 5.9% respectively.The correlation between the LAI(Leaf Area Index) and Tr(transmittence)was significant and the regression equation was Y=131.39 e-0.896 3 X(R2=0.907**).This study might provide some references for the simulation of 3D light distribution and experiment design of light measurement in other fruittrees' canopy structure optimization.