主要城市园林树种乐昌含笑光合特性研究

用Li-6400便携式光合作用测定系统对自然条件下城市园林树种乐昌含笑的光响应特性、CO2响应特性及光合作用日变化规律进行测定．结果表明：乐昌含笑的光补偿点为50μmol／m^2·s，光饱和点为1568μmol／m^2·s，表观量子效率为0．01；CO2补偿点为122．8μmol／mol，CO2饱和点为1761μmol／mol，羧化速率为0．03；光合作用日变化为单峰曲线，无光合“午休”现象，主要生理生态影响因子为光合有效辐射和气孔导度等．

Study on Photosynthetic Characteristics of Important Landscaping Tree Species Michelia chapensis in Changsha

The diurnal variation of photosynthesis, photosynthetic response and CO2 response of landscaping tree species Michelia chapensis were studied under natural urban condition by making use of Li-6400 portable photosynthesis system. The results showed that the light compensation point （LCP） of M. chapensis was 50μmol/m^2 ·s, the light saturation point （LSP） was 1 568 μmol/m^2 · s, and the apparent quantum efficiency was 0. 01. It was measured that the CO2 compensation point of the species was 122. 8 μmol/mol, CO2 saturation point was 1 761 μmol/mol, and the carboxylation efficiency was 0.03. It was demonstrated by the measurement that the diurnal variation of net photosynthetic rate （Pn） was an one-peak curve and there was no midday depression and the peak value appeared at 10：00 with 6. 31 μmol/m^2 · s. The main physio-ecological affecting factors were photosynthetically active radiation and stomatic conductance.