| With field sampling,positioning measurement and laboratory analysis,the photosynthetic and cold resistance characteristics of Seedlings of Ilex latifolia in Dashan Forest Farm in Zongyang County was studied.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 17.75?mol/?m2·s?,1769?mol/?m2·s?and 0.0384,16.21?mol/?m2·s?,1387?mol/?m2·s?and 0.0402,17.58?mol/?m2·s?,1678?mol/?m2·s?and 0.0411 and 20.88?mol/?m2·s?,945?mol/?m2·s?and 0.0267 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 12:00,13.081?mol/?m2·s?and 13:00,4.231?mol/?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(6.278?mol·m-2·s-1)>autumn(5.3915.408?mol·m-2·s-1)>summer(4.983?mol·m-2·s-1)>winter(2.013?mol·m-2·s-1).Meanwhile,the variation rule of solar energy use efficiency is spring(0.911×10-2)>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 Ilex latifolia 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,0.7318*0.8012*?,the photosynthetic rate in summer and autumn are in a significantly negative relation with PAR and Ta?-0.7904*-0.7111*?,and a significantly positive relation with RH and in winter,it is in a positive relation with Ta and RH?0.8221*?0.7438*?.This shows that all light,moist and warm are suitable for Ilex latifolia'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(2.217?mol·mmol-1)>autumn(1.512?mol·mmol-1)>summer(1.322?mol·mmol-1)>winter(1.101?mol·mmol-1);And the rule of diurnal variations of transpiration rate mean value is summer(2.954mmol·m-2·s-1)>autumn(1.771mmol·m-2·s-1)> spring(1.499 mmol·m-2·s-1)>winter(1.112mmol·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?Measured by a few green fluorescence parameters in the spring and autumn day small amplitude.Fm,Fm ',Fv,Fv/Fm,Fm/F0,Fv/F0 present obvious after the first drop in summer 8:00 18:00 litres of law,its lowest level in around 14:00,while NPQ rendering first,lowered after its peak appeared at about 12:00.Fm,Fm ',Fv,Fv/Fm,Fm/F0,Fv/F0 changes in one day in winter is first single-peak curve,lowered after its peak appeared around 14:00,and NPQ at the changes in the situation is the opposite of the day,its lowest level in around 14:00.Winter and summer seasons of Fv/Fm,Fm/F0 and Fv/F0 significantly lower than in the spring and autumn season,showed Ilex latifolia winter and summer seasons leaf PS ?electron transfer reaction center efficiency and potential activity was significantly lower than in the spring and autumn season.NPQ parameters were significantly higher in winter and summer in the spring and autumn season,showed Ilex latifolia in winter and summer have a larger proportion for absorption of light energy dissipation and protect their photosynthetic mechanism.Correlation analysis showed that the NPQ instead of air relative humidity in spring,summer and fall,has negative correlation with the temperature and light were significantly positive correlation,while in winter and its temperature has significant negative correlation.Summer Fm/F0,Fv/F0,Fv/Fm and its temperature and illumination,has negative correlation with atmospheric relative humidity has significant positive correlation.?6?In specified seasons?January,February,March,October,November and December?,the minimum value of semi-lethal temperature of Ilex latifolia appears in January(-15.78?),the maximum is in October?-5.98??,which shows that the cold resistance ability of Ilex latifolia sapling's leaf is respectively stronger and weaker in January and October.In winter?January,February,November and December?,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 Ilex latifolia sapling's leaf. |
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