Study On Impacting Process Of Veratrum Oxysepalum Invasion On Leaf Characteristics And Photosynthetic Characteristics Of Rhododendron Aureum

At present,the tundra vegetation in Changbai Mountain has undergone obvious changes,and the basic manifestation is that herbaceous plants invaded shrub tundra.Veratrum oxysepalum,an early spring herbaceous plant,used to grow only in low-altitude areas under tundra.In recent years,the temperature in Changbai Mountain has increased significantly in spring,which provides a thermal basis for the establishment of Veratrum oxysepalum in the tundra.And in the early spring,the niche is not saturated.With its strong growth advantages,Veratrum oxysepalum quickly established in the tundra,resulting in the degradation of native shrubs,and eventually the exotic species of herbs occupied the niche of native shrub vegetation.Therefore,this study takes the impact of herb invasion on the photosynthesis of tundra native shrubs as an entry point to study the degradation of photosynthetic ability of Rhododendron aureum which is the dominant species in the tundra caused by Veratrum oxysepalum invasion.In this study,the tundra on the western slope of Changbai Mountain where the herbaceous plants invasion was prominent was selected as a field experiment area.To exploring the dynamic change process of Veratrum oxysepalum invading Rhododendron aureum community,studying on the impact of Veratrum oxysepalum invasion on leaf characteristics and photosynthetic characteristics of Rhododendron aureum which is the dominant species in the tundra of Changbai Mountain,this study set up two experiments about Veratrum oxysepalum invasion process and it's effect on the photosynthetic characteristics of Rhododendron aureum,revealing the photosynthetic physiological mechanism of the degradation of Rhododendron aureum in the tundra zone of Changbai Mountain under the influence of Veratrum oxysepalum invasion.The main results are as follows:Veratrum oxysepalum has moderately invaded Rhododendron aureum community in only 3 years.In the community of Rhododendron aureum-Veratrum oxysepalum,with the degree of invasion increasing,the coverage and number of Rhododendron aureum decreased significantly,while the species and number of herbaceous plants showed an increasing trend,and the coverage and number of Veratrum oxysepalum increased significantly.All the results indicated that Veratrum oxysepalum has strong invasiveness,and can also promote the invasion of other herbs.Invasion degrees of Veratrum oxysepalum significantly affected the leaf area,specific leaf area,leaf dry weight,leaf thickness and total nitrogen content of Rhododendron aureum.With the degree of invasion increasing,the leaf area of Rhododendron aureum showed a significant downward trend during most of the growing season;leaf dry weight and specific leaf area showed a significant decrease trend in the middle and late growing season;leaf thickness showed a significant increase trend in the middle growing season,and total nitrogen content showed a significant downward trend during Mid-season.Veratrum oxysepalum invasion had no significant effect on the changes of leaf characteristics of Rhododendron aureum with time,but among the three indexes of leaf thickness,total carbon content and total nitrogen content of Rhododendron aureum,it showed that With the degree of invasion increasing,the volatility that changes with time tends to increase.The degree of Veratrum oxysepalum invasion strongly affected assimilation rate,internal CO2,stomatal conductance and water use efficiency of Rhododendron aureum.With the degree of invasion increasing,assimilation rate showed a decrease trend during the growing season;internal CO2 and stomatal conductance showed a downward trend in the middle and late growing season;and water use efficiency of showed an increase trend in the middle and late growing season.Besides,the significant effect of Veratrum oxysepalum invasion on the photosynthetic characteristics of Rhododendron aureum with time is reflected in the limiting effect of internal CO2 and stomatal conductance at the end of the growing season.It showed that the invasion of Veratrum oxysepalum reduced the resource availability of Rhododendron aureum in its competitive growth with Veratrum oxysepalum,and made Rhododendron aureum at a competitive disadvantage in photosynthesis.Invasion degrees of Veratrum oxysepalum significantly affected ETR q P at the end of the growing season,and significantly affected NPQ in the middle and late growing season.With the degree of invasion increasing,the ETR and q P showed significant decrease trends,while NPQ showed an increasing trend;and the degree of invasion has no significant effect on other indicators.The significant effect of Veratrum oxysepalum invasion on the changes of photosynthetic characteristics of Rhododendron aureum with time is reflected in the limiting effect of ETR at the end of the growing season.Therefore,from the perspective of chlorophyll fluorescence parameters,the invasion of Veratrum oxysepalum also has a certain inhibitory effect on the photosynthesis of Rhododendron aureum.From the perspective of photosynthesis,Veratrum oxysepalum invading Rhododendron aureum community has certain advantages.The warming of spring makes Veratrum oxysepalum as an early spring plant that can survive on the tundra.Because seeds germinating earlier,it has a certain niche advantage compared with other invasive herbs.And with the growth of Veratrum oxysepalum,it significantly affected the photosynthetic physiological activities of the surrounding Rhododendron aureum during the growing season,degraded the photosynthetic ability of Rhododendron aureum and eventually replaced it.