Investigations on diurnal photosynthesis variation of Pinus massoniana Lamb. with different growth vigor

The experimental materials were hybrid clones(H5,with high growth vigor),(L1,with low growth vigor) and(C,mean growth vigor) of Pinus massoniana Lamb.,the diurnal dynamics of net photosynthetic rate(Pn),transpiration rate(Tr),intercellular CO2concentration(Ci) and stomatal conductance(Gs) of canopy leave of P. massoniana were measured in situ by using a Li-6400 portable photosynthesis system. The corresponding tree height(H) and diameter(D) were also recorded. The relationships between Pn,Tr,Ci,Gsand tree growth were investigated. The results show that the diurnal changes of Pn of H5,L1 and C all displayed double peak curve at a.m. 10:00 and p.m. 16:00 respectively,the average daily value of Pn of H5 far higher than that of L1 and C; The diurnal changes of Tr of H5,L1 and C all showed double peak curve at a.m.8:00 and p.m.13:00 respectively,no significant difference between the average daily value of Tr of H5 and L1; The diurnal changes of Gs of H5,L1 and C also exhibited double peak curve,the average daily value of Gs of L1 was the largest among H5,L1 and C; The diurnal changes of Ci of H5,L1 and C showed "V-shape" curve,the average daily value of Ci of L1 reached the highest,and there was significant difference with H5. The plant height,basal diameter were highly-significantly correlated with Pn. The clone with high growth vigor had greater Pn and relatively smaller respiration consumption,which was conducive to dry matter synthesis in tree.