杏树冠层内光合有效辐射(PAR)分布规律及结构优化初探

以杏树为试材,为了解杏树冠层内透光率随树龄和叶面积指数的变化,采用LP-80型冠层分析仪测定了光合有效辐射PAR(Photosynthetically Active Radiation)在不同树龄杏树冠层三维空间上的分布情况,研究了杏树冠层内透光率随树龄(2~6 a)和叶面积指数的变化。结果表明,杏树冠层内部平均PAR的垂直分布具有随着向下累计叶面积指数的增加而递减的趋势,在冠层中上部,透光率较高,PAR递减很明显,冠层下部则维持较低水平,变化不大,在相同的天气和时间条件下不同树龄冠层内PAR同一相对高度的透光率有随树龄增加而递减的趋势,但在不同时刻不同天气条件下,即使同一棵树相同高度同一方位冠层内也具有不同的消光系数,影响杏树冠内光分布的因素是多样的,它们之间存在着复杂的关系;2~6年生杏树冠层中部的全天平均透光率分别为49.5%、30.0%、27.5%、13.4%和7.8%,冠层下部的平均透光率分别为29.1%、12.1%、10.9%、6.4%和5.9%;杏树冠层叶面积指数LAI(Leaf Area Index)与透光率呈极显著指数相关关系,其表达式为Y=131.39 e-0.896 3X(R2=0.907**);试验结果也可为果树冠层内PAR三维空间分布的模拟研究及冠层结构的优化提供试验方法和理论验证上的参考。

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.