Compare on Photosynthetic Characteristics Among 4-year-old Seedlings of Pinus yunnanensis Populations

The response characteristics curve and diurnal course of photosynthesis were compared for 4-year-old seedlings of Pinus yunnanensis populations to reveal the difference of photosynthetic characteristics and the major environment influencing factors of photosynthesis. The results showed that the imitative effect of the light response curve and CO₂ response curve were fitted by non-rectangle hyperbola model, and some response characteristic parameters were calculated. The net photosynthetic rate (P_n) increased with the increasing of the photosynthetically active radiation (PAR) and CO₂ concentrations among P.yunnanensis populations. The maximum net photosynthetic rate (P_max) increased by 44.50%-130.41% under CO₂ saturation when compared with light saturation. The diurnal change of P_n appeared a single-peak curve, and had no obvious photoinhibition phenomenon and ′midday depression′ phenomenon. The diurnal changes trend of stomatal conductance (G_s) and transpiration (T_r) were similar with that of P_n, but intercellular CO₂ concentration (C_i) was reverse. PAR, vapor pressure deficit (VPD), air humidity (RH) and air temperature (t_a) were the major environment factors influencing photosynthesis of P.yunnanensis on dry season.