Research On Photosynthesis Characteristics Of8-year’s Phoebe Bournei

This paper takes Mixed forests of eight years old Phoebe bournei and Schima superba in Jindong forest farm of Yongzhou City, Hunan Province as research object. By using LI-6400American portable photosynthesis measuring system, net photosynthesis of Phoebe bourneiplantations of photosynthetic rate, transpiration rate, water use efficiency, leaf temperature, leaf water deficit, intercellular CO2concentration, stomatal conductance, Photosynthetic Physiology ecological factors were measured. The light response curve was measured either. The main results are as follows:(1) Phoebe bournei grew more slowly in the first3years, after5years later, the growth gradually accelerated, volume growth was increased with the increase of tree age, show that Phoebe bournei is a longer fast-growing stage species.(2) In the spring, autumn and winter, diurnal variation of Pn type in upper and lower leaves of Minnan shows a single peak curve, while double peak curve in the summer, showing obvious "midday depression of photosynthesis". The average daily Pn type in different seasons ranks from big to small:Summer, Autumn, Spring Winter(3) In the spring, autumn and winter, diurnal variation of transpiration rate in upper and lower leaves of Minnan shows a single peak curve. In Summer, it is obviously double peak curve, showing midday depression phenomenon. The average daily Tr in different seasons ranks from big to small:Summer, Autumn, Spring, Winter.(4) In the spring, water use efficiency in upper and lower leaves of Phoebe bournei showed a downtrend. In Summer and Autumn, it shows double peak curve, and "three peak" curve in winter. The average daily WUE in different seasons ranks from big to small:Spring, Autumn, Winter, Summer.(5) Change trend of leaf temperature in different seasons shows single peak type, but peaks at different time. The upper and lower leaf temperature is very close at the same time in each season. Overall, the upper and lower leaf temperature ranks from high to low:summer, autumn winter, spring, which is in accord with the high and low temperature sequence.(6) The diurnal variation of Vpdl in unpper and lower leaf in different seasons shows "peak" curve. In the same season, the upper and lower leaf present the same trend. The average daily Vpdl in different seasons ranks from big to small:Summer, Spring, Autumn, Winter, which shows that Phoebe bournei photosynthetic capacity is in strong and vigorous growth period during spring and summer seasons.(7) The early morning of intercellular CO2concentration is relatively high in each season. In general, Phoebe bournei diurnal change of intercellular CO2concentration and photosynthetic rate diurnal variation in each season showed the opposite trend. In the spring,autumn and winter, changes of upper and lower leaf intercellular CO2concentration shows "U" curve,"double dip" curve in the summer---"noon break" phenomenon is obvious—hile diurnal variation of Ci is relatively slow in winter. The daily Ci sequence in different seasons ranks from high to low:Winter, Spring,Autumn,Summer. It is closely equal in Spring and Autumn.(8) In the spring,autumn and winter, stomatal conductance on the upper and lower leaf shows a single peak curve, and "double peak" curve in summer. Overall, the stomatal conductance of upper leaf is slightly higher than the lower leaf. The gap is larger in Summer and Autumn. The difference of stomatal conductance on upper and lower leaf in spring and winter is smaller. The sequence of Cond in different seasons is:Summer, Autumn, Spring, Winter.(9) The Pn value increases with the increase of PAR value. When the photosynthetic active radiation is0, the photosynthetic rate is negative in Spring, Summer and Autumn. In low light condition, Pn increases rapidly with the increase of light. As PAR continues to strengthen, the Pn is still rising, but the trend is obvious slow down. With the increase of the light intensity, the increasing range of photosynthetic rate becomes smaller and smaller, gradually stabilized, but the light inhibition is not obvious. However when the PAR exceeds a certain degree, Pn begins to show a downward trend.