中文摘要：

为了探讨西双版纳热带植物园引种植物主要定植区近地层的光合有效辐射特征及其变化规律,利用2008—2009年不同季节的小气候观测资料,分析了西双版纳热带植物园引种植物主要定植区近地层的光合有效辐射的季节和日变化特征。结果表明：西双版纳热带植物园区域的光合有效辐射具有明显的日变化和季节差异,雨季最强,旷地的光合有效辐射日总量可达406.6mol·m^-2·d^-1,雾凉季最弱,旷地光合有效辐射日总量为236.0mol·m^-2·d^-1;由于受高大树木遮蔽的影响,在沟谷林、龙脑香林和树木园的光合有效辐射数值较低;受太阳高度角变化和林冠林隙的影响,在雨季近地层光合有效辐射会出现＂突跃＂现象。各引种植物定植区近地层的光合有效辐射的数值也不同,存在地域差异和季节差异。在具有高大树木、遮蔽较大的定植区,近地层光合有效辐射的数值较小;而遮蔽较小的定植区,情况则反之,近地层光合有效辐射的季节差异与旷地相似,雨季较大,雾凉季较小。在具有高大树木、遮蔽较大的定植区,近地层光合有效辐射与旷地的比值较小,不足旷地的10%,其中在具有多层多种森林群落结构的沟谷林,其最小比值（雾凉季）仅为1.6%;而遮蔽较小的定植区比值较大（〉55%）在干热季其数值甚至与旷地相当,比值达98.7%。结果表明,西双版纳热带植物园不同引种植物定植区近地层光合有效辐射存在明显的时空异质性,这势必对引种植物,特别是栽培在林下的引种植物生长起到重要的作用。

英文摘要：

Based on the micro-climate observation data from 2008 to 2009,the diurnal and seasonal variations of photosynthetically active radiation （PAR） in the near surface layer of four introduced plant sites in Xishuangbanna Tropical Botanical Garden were analyzed. All the plant sites showed obvious diurnal and seasonal variations in PAR. The highest PAR appeared in rainy season,which reached 406.6 mol·m^-2·d^-1n open field,while the lowest one appeared in fog cool season,which was 236.0 mol·m^-2·d^-1n open field. In the sites with tall trees,including the Rain Forest Valley,Dipterocarp Garden,and Arboretum,the PAR was relatively lower. with the effects of solar elevation angle and canopy gap,there was a ＂jump up＂ for the PAR in rainy season. Spatially,the PAR appeared to be higher in the sites with tall trees. Temporally,rainy season had a higher PAR than other seasons. The PAR in the sites with tall trees and large shelters was less than 10% of that in open field,and the PAR ratio was only 1.6% in the Rain Forest Valley compared with the open field in fog cool season,which was the lowest among all the sites. However,this ratio reached 98.7% in dry hot season in the Tropical Fruits Garden,which had little shading. Generally,the temporal and spatial heterogeneities of PAR existed in different plant sites,which could definitely affect the rhythm of the introduced plant species in Xishuangbanna Tropical Botanical Garden.