【摘要】 在雨水充足的森林生态系统中光合有效辐射（PAR）是植物初级生产力的主要控制因子,同时也会对森林的垂直结构、群落组成和系统演替等产生重要的影响.为了研究秦岭典型地带性植被群落天然次生油松林近成熟龄阶段林内不同层次光合有效辐射（PARs）的时空分布特征及相互关系,在陕西宁陕县秦岭森林生态系统国家野外科学观测研究站油松林内4个层次（第1层:灌木层,PAR₁;第Ⅱ层:林冠下层,PAR₂;第Ⅲ层:林冠中层,PAR₃;第Ⅳ层:林冠顶层,PAR₄）对其PARs进行长期定位观测.本研究对2007和2008连续两年的实测数据进行分析研究结果表明:林冠结构对PARs影响显著,PARs从林冠顶层到灌木层垂直衰减十分明显.2007和2008年油松林PAR₄、PAR₃、PAR₂和PAR₁的年总量分别为7604.68和7939.77mol·m^-2、1436.70和1389.98mol·m^-2、1503.42和1392.12mol·m^-2、1000.68和917.11mol·m^-2;全年相对光量子通量密度RPFD₃、RPFD₂、RPFD₁分别为18.89%和17.51%、19.77%和17.53%、13.16%和11.55%.PARs时间变化上表明,PARs月均值曲线2007年呈多峰变化,2008年呈单峰变化.PARs月均值均在5月份达到最高,最低值分别出现在12月份（2007）和1月份（2008）.2007和2008年备层PARs全年日总量平均值间相差较小,春、夏生长季PARs日最高值和日平均值均明显高于秋、冬非生长季.更多还原

【Abstract】 Photosynthetically active radiation（PAR） is the primary control of plant primary productivity in humid ecosystem,and its temporal dynamics and vertical attenuation shape forest vertical structure,community assembly,and succession trajectory of forest ecosystem.The objective of this study is to improve our understanding of temporal and spatial distribution of photosynthetically active radiation（PARs） at different canopy layers in a secondary P.tabulaeformis forest approaching maturity in Qinling National Forest Ecosystem Research Station,Ningshan County,Shaanxi.We continuously measured PARs at four canopy layers（PAR₁:shrub;PAR₂:understory;PAR₃:middle canopy;PAR₄:1.5m above canopy boundary layer） in a long-term meteorological observation project.In this study,we analyzed data from2007 and 2008.Canopy structure resulted in a strong vertical attenuation of PAR values from the canopy boundary layer to forest floor.The annual values of PAR₄,PAR₃,PAR₂,and PAR₁ of2007 and 2008 were 7604.68 and 7939.77mol·m^-2,1436.70 and 1389.98mol·m^-2,1503.42 and 1392.12mol·m^-2,1000.68 and 917.11mol·m^-2,respectively.The RPFD₃（relative photosynthesis photon flux density）,RPFD₂ and RPFD₁ of 2007 and 2008 were18.89%and 17.51%,19.77 and 17.53%,13.16%and 11.55%,respectively.The temporal evolution of PARs was evidenced.Multiple peaks in monthly mean PARs were observed in2007,but only a single peak occurred in 2008.The maximum of monthly PARs mean values appeared in May for both years and the minimum of monthly PARs mean values occurred in December during 2007 and in January during 2008.Little differences were observed in the annual mean daily PARs values in 2007 and 2008.The maximum and mean of daily PARs values in growing season（spring and summer） was significantly higher than that in non-growing season（autumn and winter）.更多还原