| With field sampling, positioning measurement and laboratory analysis, the paper studies the photosynthetic and cold resistance characteristics of six-year-old Daphniphyllum macropodum of Dashan Forest Farm in Zongyang Country. The main results are as follows:(1) According to the light response curves of four different seasons, the sapling’s light-compensation point(LCP), light-saturation point(LSP) and the apparent quantum yield(AQY) are 18.25 μmol/(m2·s),1773μmol/(m2·s) and 0.0452,16.19μmol/(m2·s), 1405μmol/(m2·s) and 0.0337,17.63μmol/(m2·s),1655μmol/(m2·s) and 0.0406 and 21.03μmol/(m2·s),932μmol/(m2·s) and 0.0258 in spring, summer, autumn and winter respectively. In different reasons, the sapling has different light utilization characteristics.(2)In spring and winter, the diurnal variation of net photosynthetic rate shows a single peak curve, and the appearance time and value of peak values are 12:00,13.081μmol/ (m2·s) and 13:00,4.128μmol/(m2·s) respectively. And the curve present a double peak form in summer and autumn, besides, the "lunch break" exists. The variation rule of diurnal variation of net photosynthetic rate is spring (6.337 μmol·m-2·s-1)>autumn (5.408μmol·m-2·s-1)>summer (4.972μmol·m-2·s-1)>winter (2.128μmol·m-2·s-1). Meanwhile, the variation rule of solar energy use efficiency is spring (0.907×10×-2) >autumn (0.857×10-2)>summer (0.832×10-2)>winter (0.699×10-2).(3)Through path analysis and stepwise regression analysis, the result shows that in different season, the main ecological factors affecting the photosynthetic rate of Daphniphyllum macropodum are different. The photosynthetic rate in spring is in a significantly positive relation with photosynthetic active radiation (PAR), atmospheric temperature (Ta) and atmospheric relative humidity (RH,0.6826*～0.7271*), the photosynthetic rate in summer and autumn are in a significantly negative relation with PAR and Ta (-0.7428*～0.5381*), and a significantly positive relation with RH and in winter, it is in a positive relation with Ta and RH (0.8133*,0.4952*). This shows that all light, moist and warm are suitable for Daphniphyllum macropodum’s saplings in spring. Both summer and autumn, it favorite climate are cool and humid. Warm and humid are appropriate in winter.(4) Water use efficiency is directly affected with photosynthesis and transpiration.The trend of diurnal variations of WUE mean value in different seasons is spring (2.100 μmol·mmol-1)>autumn (1.482μmol·mmol-1)>summer (1.275μmol·mmol-1) >winter (1.039μmol·mmol-1);And the rule of diurnal variations of transpiration rate mean value is summer (2.933mmol·m-2·s-1)>autumn (1.762mmol·m-2·s-1)> spring (1.508 mmol·m-2·s-1)>winter (1.091mmol·m-2·s-1). The sapling grow with high transpiration rate and low WUE in summer. This shows that sprinkling water and other measures should be taken, especially in summer.(5) The daily change range of every chlorophyll fluorescence parameter in spring and autumn is small. The values of Fo(minimal fluorescence)and NPQ (non—photochemical quenching)from 8:00 to 18:00 in summer presents a ascending - descending trend and the highest value is at 12:00 and 14:00 respectively, but the values of Fm(maximal fluorescence), Fm’(actual maximal fluorescence), Fv(variable fluorescence),Fv/Fm(optimal/maximal photochemical efficiency of PS Ⅱ),Fm/Fo(electron transfer rate)and Fv/Fo(potential activity of PS Ⅱ) from 8:00 to 18:00 in summer obviously show a descending-ascending trend and the lowest value is at 12:00. The daily change of Fo in winter is small, but the values of Fm, Fm’,Fv, Fv/Fm, Fm/Fo and Fv/Fo from 8:00 to 16:00 in winter, however, is single peak and the highest value is between 12:00 and 14: 00. The daily change trend of NPQ in winter, however, is contrary to those parameters mention above and the lowest value is between 12:00 and 14:00. The fact that the values of Fv/Fm, Fm/Fo and Fv/Fo in spring and autumn are obviously higher than these in summer and winter showed that the maximal photochemical efficiency, the electron transfer rate and the potential activity of PS II in spring and autumn is more effective. On the contrary, the value of NPQ in winter and summer is obviously higher these in spring and autumn, indicating that higher proportion of light energy absorb in winter and summer is used to avoid the destruction of photosynthetic tissue through hot dissipation.(6)In specified seasons (January, February, March, October, November and December), the minimum value of semi-lethal temperature of Daphniphyllum macropodum appears in January (-15.62℃), the maximum is in October (-6.23℃), which shows that the cold resistance ability of Daphniphyllum macropodum sapling’s leaf is respectively stronger and weaker in January and October. In winter (January, February, November andDecember), the leaf’s soluble sugar content is in a significantly negative relation with its semi-lethal temperature. We can see that it is an important mechanism to improve cold resistance ability when increase its soluble sugar content. Meanwhile, the leaf’s MDA content is significantly higher than March and October, which shows the winter’s low temperature in test area is a significant threat to Daphniphyllum macropodum sapling’s leaf. |
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