杨树无性系幼苗光合作用的光抑制

为更多地了解自然条件下活体叶片的光抑制，以LI－6200便携式光合系统测定了杨树无性系幼苗叶片叶的净光合速率（Pn）、表观量子产量（AQY）等，比色法测定了超氧化物歧化酶（SOD）活性。结果表明，中午Pn降低，出现光合“午休”现象，此时Pn受非气孔因素限制，Pn的降低与气孔关闭关系不大。低湿、高温、强光条件下杨树无性系幼苗叶片AQY降低，发生了明显的光抑制。SOD对光合作用具有保护作用，SOD抑制剂使光抑制加剧，抗氧化剂使光抑制得到缓解，表明光抑制的发生了可能与活性氧的积累有关。

PHOTOINHIBITION OF PHOTOSYNTHESIS OF ATTACHED LEAVES IN POPLAR CLONE SEEDLINGS

Net photosynthetic rate(Pn) and apparent quantum yield(AQY) were measured with Li-6200 portable photosynthesis system in parallel with superoxide dismutase(SOD) activity determined with UV-754 ultraviolet spectrophotometer in attached leaves of poplar clone seedlings. It was found that Pn decreased,and photosynthesis depression phenomenon occurred at noon. At this conditions Pn was limited by non-stomatal factors,and the decline of Pn had no relations with the closure of stomata. AQY in attached leaves of poplar clone seedlings decreased and photoinhibition of photosynthesis occurred evidently under stressful conditions. SOD could protect photosynthesis. The inhibitor of SOD could intensified, while antioxidant could alleviated, photoinhibition of photosynthesis. The conclusion was that photoinhibition of photosynthesis in attached leaves of poplar clone seedlings had intrinsic relations with the accumulation of reactive oxygen species.