The daily changes of chlorophyll fluorescence parameters of Machilus leptophylla in different seasons were studied. Results showed that the amplitude of daily change in chlorophyll fluorescence parameters was small in spring and autumn. The values of minimal fluorescence ( Fo) , maximal fluorescence ( Fm), actual maximum fluorescence (Fm) , variable fluorescence (F,), optimal/maximum photochemical efficiency of PS II ( F,/Fa) , electron transfer rate (Fm/F0) and potential activity of PS II (Ft/F0) exhibited a descending trend at first, and then turned into an ascending trend from 8 :00 to 18:00 in summer, and the lowest value was at 12:00. However, the value of non-photochemical quenching (NPQ) presented an ascending trend at first, and then turned into a descending trend from 8;00 to 18:00 in summer, and the highest value was at 14:00. The daily change of Fo, Fm, F'·, Fv, F/ m, Fm/F0 and F/Fo in winter could be described by a unimodal curve, and the highest value occurred between 12;00 and 14:00. The daily change of NPQ in winter, however, was contrary to those parameters mentioned above, and the lowest value occurred between 12:00 and 14:00. The Fy Fo value in winter was obviously lower than that in other seasons. The Fm/ Fo value in spring and autumn was obviously higher than that in summer and winter, indicating that the electron transfer rate of PS II in spring and autumn was more effective. The obviously higher Fy Fo value in spring and autumn also indicated that the potential activity of PS II in these seasons was higher. On the contrary, the NPQ value in winter and summer was obviously higher than that in spring and autumn, indicating that a higher proportion of light energy absorbed in winter and summer was used to avoid the destruction of photosynthetic tissue through hot dissipation.%对不同季节华东楠叶片主要叶绿素荧光参数的日变化进行了测定.结果表明,华东楠叶绿素荧光参数在春季和秋季的日变化幅度较小.夏季8:00-18:00,F0、Fm、F'm、Fv、Fv／Fm、Fm/F0、Fv/F0呈现先降后升的规律,12:00左右出现最低值,而非光化学猝灭系数(NPQ)则呈现先升后降的规律,最高值出现在14:00左右.F0、Fm、F'm、Fv、Fv/Fm、Fm/F0、Fv/F0在冬季一天中的变化呈单峰曲线,最大值出现在12:00-14:00;而NPQ在一天中的变化情况则正好相反,最小值出现在12:00-14:00.冬季的Fv/Fm显著低于春、夏、秋三季.春季和秋季的Fm/F0极显著高于夏季和冬季,表明华东楠在夏季和冬季叶片PSⅡ反应中心电子传递效率显著低于春季和秋季.春季和秋季的Fv/F0极显著高于夏季和冬季,表明春季和秋季华东楠叶片PSⅡ的潜在活性高于夏季和冬季.华东楠冬季和夏季的NPQ显著高于春季和秋季,表明华东楠在冬季和夏季吸收的光能有较大比例用于耗散而保护自身的光合机构.
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