中文摘要：

利用长白山红松针阔叶混交林连续3年的光合有效辐射（PAR）观测数据，与林冠上方PAR值相对比，分析了林冠下5个不同水平位置探头的PAR时空特征．结果表明：林木冠层上方的PAR日总量年变化呈双峰甚至多峰趋势，主要受降水和云雾等天气状况的影响；林下PAR日总量年变化表现为非生长季与冠层上方变化趋势一致，在生长季数值较小且趋于稳定．典型晴天时林下5个探头的PAR值在时间和大小分布上有较大差异．在空间变化上，非生长季林下PAR变异系数较小，约为0．15；生长季的变异系数较大，在0．22以上，最高值在8月．生长季典型晴天太阳高度角为38°-48°区间（9：00—19：00和13：00—14：00）时，林下以尺空间变化较大．

英文摘要：

Based on the data of three years successive automatic measurement with five horizontal quantum PAR sensors, this paper studied the spatiotemporal characteristics of photosynthetically active radiation （PAR） in the understory of Korean pine and broadleaved mixed forest in Changbai Mountains, in contrast with above-canopy PAR. It was found that the annual dynamics of abovecanopy PAR showed two or more peaks, which was mainly affected by the weather conditions such as cloudy, foggy and rainy events. The annual dynamics of understory PAR followed the same trend of above-canopy PAR in non-growth season, but was steady and lower in numerical value in growth season. On clear days, larger differences were observed in the diurnal variation and frequency distribution of the understory PAR. As for the spatial variation of the understory PAR, the coefficient of variation （CV） was smaller in non-growth season （about 0. 15 ） than in growth season （ 〉0. 22）, with the greatest in August. On the clear days in growth season, the understory PAR had a greater spatial variation when the solar elevation angle was between 38°and 48° （ at 9：00-10：00 or 13：00 -14：00）.