黑石顶森林群落光能的时空变化与利用效率

The Variation of PAR and Its Effects on NPR of Plants in Heishiding Lower Subtropical Forest

分析了黑石顶森林群落各高度层光合有效辐射（ＰＡＲ）的季节变化、昼夜变化、垂直空间方面的变化规律及其对植物光合作用的影响．研究表明，光量子通量密度（ＰＦＤ）从群落第一层至第四层呈指数形式减少，群落第四层常小于１．０ｍｏｌ·ｍ－２·ｄ－１．群落中植物叶片净光合作用速率（ＮＰＲ）是：第一层＞第二层＞第三层＞第四层，同一高度层植物叶片ＮＰＲ比较接近，但也存在物种间的差异．ＰＦＤ是影响植物光合作用的最主要因子，第一层植物接受充足的ＰＦＤ，能进行有效的光合作用，群落内部各层的ＰＦＤ不能满足植物光合作用的需要，叶片随ＰＦＤ的增加而同步增加．冬季ＰＦＤ较小时第四层植物的净光合作用时常为负值．群落中叶面积指数为５～７，并随季节的变化而变化．群落的光量子利用效率以第四层植物最高，第一层植物最低。

Photosynthetically active radiation (PAR) and net photosynhetic rate (NPR) of plants have been measured with a 90￣120 minute interval from sunrise to sunset for 9 species selected in Heishiding lower subtropical forest from May ,1992 to May, 1993. The forest was investigated at four height levels: layer 1 (16￣21 m),layer 2 (10￣16 m), layer 3 (3￣10 m) and layer 4 (0￣3 m). The daily accumulated photon flux density (PFD) were 7 242 3￣30 501 2 mol·m -2 ·d -1 in the layer 1 from winter to autumn, the relative photon flux density were 100%,12%,6%,3% in layer 1,2,3 and 4, respectively. Total daily PFD in layer 4 is often below 1 0 mol·m -2 ·d -1 and measurement as lowest as 0 3 mol -2 ·m -2 ·d -1 has been recorded .Light environments and NPR of plants in four layers of the forest have been compared. The mean NPR of plants were about 2 0￣4 0 μmol·m -2 ·s -1 in layer 1,1 0￣2 0 μmol·m -2 ·s -1 in layer 2 and 3, below 1 0 μmol·m -2 ·s -1 in layer 4. The quantum efficiency of species from layer 1 to layer 4 were 0 01￣0 02, 0 02￣0 03,0 02￣0 03,0 3￣0 05. High quantum efficiency was recorded in plants in low light environment.