毛竹气体交换特征

 为了探讨毛竹Phyllostachys pubescens叶片光合作用的时空动态变化规律，运用Li-6400便携式光合作用测定仪测定了毛竹叶片的气体交换日变化及林冠不同层次叶片对光照强度的响应。结果表明：①毛竹叶片的净光合速率日变化规律表现为不是特别明显的双峰型曲线，但具有“光合午休”现象，上午的峰值明显大于下午的峰值；②蒸腾速率的日变化规律呈单峰曲线，而水分利用效率日变化规律呈双峰型曲线，且与净光合速率的日变化趋势相似；③毛竹林冠上、下层次叶片的净光合速率日变化规律一致，但在相同的光照强度下，上层的净光合速率高于下层，毛竹林冠上层的叶片较下层的叶片具有更强的适应强光的能力。图6参22

Gas exchange with Phyllostachys pubescens on Mount Tianmu，Zhejiang Province

Moso bamboo（Phyllostachys pubescens） is a fast growing bamboo species with important economic and ecological value. The objective is to grasp of the spatio-temporal dynamics of photosynthesis in moso bamboo leaf. In autumn 2006，a Li-6400 portable photosynthesis system was set up in natural field conditions to determine diurnal variation of gas exchange and response of photosynthesis to light intensities in different layers of the bamboo canopy （1st－7th branches from low to up was upper layer，8th - 14th was middle layer，and≥15th was upper layer）. Results showed that for diurnal changes in autumn，the net photosynthetic rate（Pn） had a double-peaked curve with peaks at about 09:00（am） and about 15:00 （pm） and a “midday depression” from 11:00 －14:00，which was due to the absence of irradiance and closure of some stomata. Also，the diurnal transpiration rate was a single-peaked curve，while the diurnal water use efficiency（WUE） was a double-peaked curve. Additionally，light response in the upper and lower layers of the bamboo stand showed that with the same photosynthetic photon flux density，Pn was greater in the upper layer. Adaptations of leaves in the two layers may have caused the difference light intensities with leaves in the upper layer better adapted to the stronger light. ［Ch，6 fig. 22 ref.］