Effects Of Nitrogen Deposition On Ecophysiological Characteristics Of Competing Plants In The Tundra Of Changbai Mountains

In this paper,a two-year artificial nitrogen deposition experiment was carried out in the tundra zone of the west slope of Changbai Mountain,and the dominant species of Rhododendron aureum and Deyeuxia angustifolia in this area were studied.By comparing the changes of ecophysiological characteristics between the two plants,the effects of the increase of nitrogen deposition on the growth and interspecific relationship of native plants and invasive plants are discussed,which is of great significance to reveal the impact of invasive plants on the native plant community and the adaptation and diffusion mechanism of invasive plants under the background of the increase of global nitrogen deposition.The main conclusions of this paper are as follows:(1)Nitrogen addition can change the morphological characteristics of plant growth,which can not only promote plant growth,but also inhibit.With the increase of nitrogen application,the promoting effect was weakened and the inhibiting effect was strengthened.The effect of nitrogen addition was different between rhododendron aureum and deyeuxia angustifolia.As a perennial evergreen shrub,rhododendron aureum grows slowly and has a strong tolerance to environmental mutation.The effect of nitrogen addition on rhododendron cowhide was weak.The growth rate of deyeuxia angustifolia was fast and sensitive to nitrogen addition.A small amount of nitrogen addition promoted the growth of deyeuxia angustifolia.With the increase of nitrogen addition,the inhibition of deyeuxia angustifolia was stronger.(2)Nitrogen addition changed the physiological process of plants.The nitrogen content in the stems of rhododendron aureum and deyeuxia angustifolia increased rapidly,but in the leaves it did not change significantly.It can be seen that when the nitrogen element is limited,rhododendron aureum and deyeuxia angustifolia give priority to the supply of leaves;and the increase of nitrogen content in stems will also affect the absorption of other nutrients by plants: More photosynthetic products were fixed in rhododendron aureum,so the carbon content increased.However,the carbon content in deyeuxia angustifolia was not affected.The lower addition of nitrogen can promote the absorption of phosphorus,while the higher addition of nitrogen can inhibit it.Nitrogen addition did not obviously affect the soluble sugar content of leaves,but the soluble sugar content of stems decreased significantly,which can be seen that it affected the transport process of soluble sugar from leaves to roots.The phosphorus content of deyeuxia angustifolia decreased significantly with high concentration of nitrogen,but there was no obvious change in rhododendron aureum.(3)There is an obvious competitive relationship between Rhododendron aureum and Deyeuxia angustifolia.Herbal invasion significantly inhibited the growth of Rhododendron aureum,which was the primary dominant shrub species in the tundra of Changbai Mountain.The more serious the invasion,the more obvious the inhibition effect on rhododendron aureum.However,it has little effect on itself,beyond a certain density range may inhibit its growth.Nitrogen addition improved the original nutrient conditions,and a small amount of nitrogen addition promoted the growth of deyeuxia angustifolia obviously.Especially in the case of severe invasion,the addition of nitrogen can get rid of the limitation of nitrogen,and it is obviously in a dominant position in the competition with rhododendron aureum.(4)The interaction between nitrogen application and herbal invasion was more obvious than that of single nitrogen application or invasion,and herbal invasion alleviated the negative effect of high concentration of nitrogen addition on Deyeuxia angustifolia.(5)Thus,on the premise that the nitrogen deposition level continues to increase without mutation,nitrogen deposition increases the competitive advantage of invasive plant deyeuxia angustifolia by changing the growth morphological characteristics and physiological processes of rhododendron aureum and deyeuxia angustifolia.Besides,with the increase of chrysanthemum ratio,the competitive advantage of chrysanthemum was strengthened.Changbai Mountain shrub tundra is bound to meadow eventually.Even if the level of nitrogen deposition increases significantly in the future,the growth of deyeuxia angustifolia is inhibited,but the inhibition effect is limited in the areas with high microphylla density.