Study on the Photosynthesis Diurnal Variations of the Nematodiasis-resistant Clones of Pinus massoniana in Summer

The net photosynthetic rate(Pn) of the needles of the nematodiasis-resistant clones of Pinus massoniana were measured with Li-6400XT Portable Photosynthesis Analyzer to study the relationship between the diurnal variations of the Pn in summer and the physio-ecological factors.The following are the results.1.The diurnal variation trend of the Pn of the nematodiasis-resistant Pinus massoniana clones showed a double-peak curve with the peaks at 10:00 and 15:00 and had an obvious phenomenon of midday depression.The phenomenon was caused not by shortage of CO2 among mesophyll cells arising from the decrease of stomatal conductance,but mainly by non-stomatal restrictions.2.The Pn had significant correlation with the intercellular CO2 concentration(Ci),transpiration rate(Tr),air temperature(Tair),leaf temperature(Tleaf) and photosynthetically active radiation(PAR),and path analysis showed that the PAR was the main factor influencing the diurnal variations of the Pn.