| The diurnal changes of photosynthesis of 1-year and 2-year needles for individuals of Pinus taiwanensis, growing at different ages and in different site conditions at 1400m altitude in Huangshan Mountains, were measured in field in different seasons using Li-6400 photosynthetic system. The contents of chlorophyll and nitrogen and the chlorophyll fluorescence changes for the needles were determined as well. The age classes for the pine trees measured were separated as Juvenile (<5years), young to middle age (15~20 years) and middle age (50~60 years). The growing conditions were classified as two categories: deep and fertile soil, shallow and infertile soil. Furthermore, the effects of physiological factors (stomatal conduction, CO2 concentration in cell clearance, etc.) and ecological factors (photosynthetic available radiation, temperature, relative humidity, etc.) on photosynthetic rate were analyzed in the paper. The results showed as following:⑴The light compensation point and saturated point of P.taiwanensis were about 110 and 1099μmol photons m-2 s-1 respectively, while the apparent quantum efficiency was 0.017; which showed that the P.taiwanensis is heliophilous plant, and has high adaptability to higher light intensity.⑵For all the individuals measured, their 1-year and 2-year needles have obvious diurnal changes in photosynthetic rate, the curves of diurnal changes in photosynthetic rate showed double-peaked at midday in spring, summer and autumn; while single-peaked in winner. Generally, the value of first peak in the curve was higher than that of second one. The values of both the first peak and the valley in the curve appeared to increase with the increasing of age for individuals measured. The seasonal change of photosynthesis indicated that the photosynthesis rate for both values of peak and valley in the diurnal variation curve was highest in summer, then autumn, spring, winter successively.⑶P.taiwanensis had photosynthetic depression at midday in spring, summer and autumn; while not in winner. The characteristic of photosynthesis showed that the photosynthetic rate had significant relationship with tree age and needle age, but insignificant with site conditions. That showed the characteristic of barren-resistant of P.taiwanensis.⑷Regress analysis showed that the most significant factors affecting photosynthetic diurnal changes were CO2 concentration in cell clearance (Ci) and stomatal conduction (Cond), followed by ecological factors such as photosynthetic active radiance, relative humidity etc. A multivariable regulation was built in the paper to describe the interrelation between the photosynthesis rate and the affecting factor, which just for 1-year needles of whole measured individuals and for summer season only.⑸In early growth days, chlorophyll contents were not the factors mostly affected photosynthetic rate. Tree age, needle age and site conditions were also not the factors mostly affect chlorophyll contents. But in metaphase and telophase of growth, chlorophyll contents and photosynthetic rate had significant correlativity, and had a little relationship with needle age and tree age, but insignificant with site conditions.⑹The nitrogen contents of 1-year needles were higher than 2-year needles. And in the same age, the trees growing in rich and deep soil had higher nitrogen contents than in shallow and infertile soil. While chlorophyll, the nitrogen contents had the tendency of increasing with the age of individuals measured.⑺Although the seedlings of P.taiwanensis had photoinhibition, the photochemical efficiency of PSⅡwere uninfluenced. When photoinhibition occurred at 13:00, NPQ sudden increased to dissipate excrescent irradiance to protect plants. |
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