阔叶红松林林冠空隙光强异质性对红松幼树生长的影响

Effects of light intensity heterogeneity in gaps of broadleaved Korean pine forest in Changbai Mountains on Pinus koraiensis seedlings growth

利用Li-6400光合测定系统,研究了长白山阔叶红松林4个不同尺度林窗内光照强度的异质性,分析红松幼树在林窗内9个方位的光合作用日变化特征.结果表明：林窗内9个方位出现光合有效辐射（PAR）峰值顺序为：西实际林窗、北扩展林窗、林窗中心〉南实际林窗、南扩展林窗、东扩展林窗、东实际林窗〉西扩展林窗、北实际林窗,光照呈东-西、南-北不对称分布,光照梯度在西、北方向变化较大,但各方向距中心不同距离的日均PAR无显著差异.林窗Ⅰ~Ⅳ日均PAR分别为21.85、45.57、66.02和23.48μmol.m-2.s-1,相互之间均达显著差异水平（P〈0.05）.PAR与净光合速率（Pn）呈显著正相关,且相关系数随PAR增大而增大.随林窗面积的增大,PAR和Pn均先增大后减小;当林窗面积为267 m2时,二者同时达到最大值.

By using a Li-6400 portable photosynthesis system, this paper studied the heterogeneity of light intensity in four different size gaps of a broadleaved Korean pine forest in Changbai Mountains, and analyzed the diurnal change of the photosynthesis of Pinus koraiensis saplings in the gaps. In the nine orientations within the gaps, the peak value of the photosynthetically active radiation （PAR） varied in the sequence of west of actual gap, north of extended gap, gap center 〉 south of actual gap, south of extended gap, east of extended gap, east of actual gap 〉 west of extended gap, north of actual gap. Light distribution was dissymmetry in the orientations of east-west and south-north, with the variation in west and north being more significant than that in other orientations. There was no significant difference in the average PAR among the positions within specific orientations. The average PAR of the four gaps from I to IV was 21.85, 45.57, 66.02, and 23.48 umol · m^-2 · s^-1, respectively, and the difference was statistically significant （P 〈0. 05）. PAR had a significant positive correlation with net photosynthetic rate （P,）, and the correlation coefficient increased with increasing PAR. With the increase of gap size, both the PAR and the P,, of P. koraiensis saplings increased first and decreased then, with the maximum values appeared at 267 m2 of gap size.