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 50 μmol/m2·s,the light saturation point(LSP) was 1 568 μmol/m2·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/m2·s.The main physio-ecological affecting factors were photosynthetically active radiation and stomatic conductance.