Photosynthetic Characteristics Of Dominant Plants In Changbai Mountain Tundra And Their Responses To Nitrogen Deposition And Herbaceous Invasion

Primary shrub vegetation in the tundra of Changbai Mountain is degenerating.The photosynthetic characteristics and leaf characteristics of the western slope lobule and Rhododendron of Changbai Mountain tundra were studied under the effect of nitrogen deposition,herbaceous invasion and the superposition of nitrogen settlement and herbaceous invasion under the effect of photosynthesis.The main dominant plants of the Changbai Mountain tundra,including Deyeuxia angustifolia and Rhododendron aureum,were selected for the study of nitrogen deposition and photosynthetic characteristics of plants for two consecutive years.The study revealed the physiological mechanism of the invasion of the tundra with herbaceous plants and provided information for the study of the trend of changes in nitrogen deposition in the tundra Rhododendron clumps.The main results are as follows:Types of nitrogen can significantly affect the chlorophyll content of Rhododendron aureum,the chlorophyll content of Rhododendron aureum was increased under the application of ammonium nitrate NH₄NO₃.Under ammonium nitrate NH₄NO₃ and potassium nitrate KNO₃,photosynthetic rate increased significantly,while ammonium sulfates?NH₄?₂SO₄ did not significantly increase photosynthetic rate.The leaf thickness of Rhododendron aureum was thinner and the leaf area increased with the increase of the coverage of Deyeuxia angustifolia.It shows that with the increase of Deyeuxia angustifolia coverage,the leaves of Rhododendron aureum tend to grow larger and thinner in order to get more sunlight.From the perspective of leaf characteristics,high concentration of nitrogen could significantly increase the leaf thickness of Rhododendron aureum,and the aggravation of herbaceous invasion significantly reduced the chlorophyll content and leaf area of the leaves of Rhododendron aureum.Nitrogen application could significantly increase leaf area of Deyeuxia angustifolia and increase leaf thickness and chlorophyll to a certain extent,while herbaceous invasion had no significant effect on leaf characteristics.From the perspective of photosynthetic parameters,the photosynthetic rate of Rhododendron aureum increased significantly with the increase of nitrogen concentration,and decreased with the increase of the invasion degree,and Gs decreased with the aggravation of the degree of invasion.Nitrogen concentration was the main factor affecting photosynthetic parameters of Deyeuxia angustifolia.The invasion degree of herbaceous plants had no significant effect on photosynthetic parameters.With the increase of nitrogen concentration,A and Gs of Deyeuxia angustifolia increased significantly.According to the photosynthetic response curve,the photosynthetic capacity of Rhododendron aureum is the highest among several plants.The light saturation point and the light compensation point of Deyeuxia angustifolia are the lowest in several plants,and there are obvious light suppression when the light intensity is more than1000 mol m^-2s^-1,which may be due to Deyeuxia angustifolia is a kind of undergrowth plant.From the monthly change of plant photosynthesis,the maximum net photosynthetic rate of Rhododendron aureum is not higher than that of several other plants,but the duration of photosynthesis is the longest.The activities of photosynthetic activities of Rhododendron aureum are throughout the growing season,and even in the snow covered season.In August,the physiological activity of Rhododendron aureum was most vigorous,and the net photosynthetic rate reached about 11?mol m^-2s^-1.The net photosynthetic rate of Deyeuxia angustifolia reaches14?mol m^-2s^-1 in July and August.Ligularia jamesii was mainly active in late June,and the net photosynthetic rate could reach 12.85?mol m^-2s^-1.Veratrum oxysepalum was mainly active in early July,and its net photosynthetic rate reached 13.68?mol m^-2s^-1.The active period of Sanguisorba stipulate is relatively longer.From late June to early July,the net photosynthetic rate can reach 10.42-12.15?mol m^-2s^-1.