The Annual And Diurnal Changes Of Photo Synthetic Characteristics And The Relationship With Ecological Factors In Endangered Plants Of Gaoligong Mountains

The author uses the Li-6400XT portable photosynthesis system to measure continuously the photosynthetic characteristics(including net photosynthetic rate,stomatal conductance,transpiration rate,diurnal variation of intercellular CO2 concentration,correlation analysis of net photosynthetic rate and environmental factors,net photosynthetic rate--light response,net photosynthetic rate—CO2 response)of the seedlings of the first-class protected plant Alcimandra cathcardii,as well as endangered plant Aidia shweliensis,and Helicia shweliensis in three different habitats(grassland,greenhouse and undergrowth)of southern Gaoligong Mountain in spring,summer and winter weather conditions,to understand the photosynthetic characteristics of three plants and offer reference for its scientific protection.The results show:(1)The diurnal variation curves of photosynthetically active radiation values in the three habitats of Alcimandra cathcardii seedlings grown in different seasons were all unimodal.There was no "noon break"phenomenon in the daily variation of net photosynthetic rate,transpiration rate and stomatal conductance of seedlings in spring and winter.However,in summer,the diurnal variation of the above-mentioned values showed"noon break".In all seasons,the variation trend of the CO2 concentration was opposite to that of other photosynthetic parameters.In spring and winter,in all habitats,the net photo synthetic rate of seedlings was the most affected by photosynthetically active radiation,while in summer,the effect of photosynthetically active radiation and relative air humidity was the same.The values of light saturation point,light compensation point and CO2 compensation point in grassland and undergrowth were decreased with the seasonal variation,where the values in greenhouse were basically unchanged.(2)The diurnal variation curves of photosynthetically active radiation values in the three habitats of Helicia shweliensis seedlings grown in different seasons were all unimodal.There was "noon break" phenomenon in the daily variation of net photosynthetic rate,transpiration rate and stomatal conductance of seedlings in spring and summer,with long "noon break" in summer.However,in winter,the diurnal variation of the above-mentioned values showed "noon break".In all seasons,the variation trend of the CO2 concentration was opposite to that of other photosynthetic parameters.In all seasons,in all habitats,the net photo synthetic rate of seedlings was the most affected by photosynthetically active radiation.In all seasons,the light response curve of the seedlings was similar to the CO2 response curve.The light saturation point values of the seedlings in all habitats were the highest in winter,and the light compensation points were basically unchanged in three seasons.In grassland and undergrowth,the seedlings' CO2 compensation point values in spring and winter were higher than those in summer,while in the greenhouse,the values of three seasons were basically the same.(3)The diurnal variation curves of photosynthetically active radiation values in the three habitats of Aidia shweliensis seedlings grown in different seasons were all unimodal.In spring,there was "noon break"phenomenon in the daily variation of net photosynthetic rate,transpiration rate and stomatal conductance of seedlings in grassland and greenhouse,with no "noon break" in undergrowth.In summer,the diurnal variation of the above-mentioned values showed "noon break" in all seasons in all habitats.In winter,there was no "noon break".In all season,the net photosynthetic rate of seedlings was the most affected by photosynthetically active radiation.In spring,the light compensation point value of the seedlings in undergrowth was higher than that of the grassland and the greenhouse seedlings.The light saturation point value and the CO2 compensation point value of the grassland and undergrowth seedlings were higher than that of the greenhouse seedlings.In summer and winter,the light compensation point was the lowest in the greenhouse,there was little difference in the light saturation point values in all habitats,and the CO2 compensation point was the lowest in the grassland.In winter,the CO2 compensation point of grassland and greenhouse seedlings was higher than that of undergrowth seedlings.