Distribution Of Plant Communities Along Environmental Gradients And Changes Of Dominant Species Coverage At Alpine Tundra Of Northern Changbai Mountain

Under the influence of global climate change,the alpine and subalpine plant communities have undergone obvious changes.As a typical alpine tundra in China,the tundra of Changbai Mountain has also experienced herbaceous invasion in the past 30 years,especially in the west slope.Under the influence of the invading herbs represented by Calamagrostis angustifolia,some of the native shrubs in the tundra were degraded,and the vegetation showed a tendency of meadow.However,at alpine tundra of northern and southern Changbai Mountain,this kind of herb invasion is relatively moderate,what factors may limit herb invasion is unclear.In this study,tundra of northern Changbai Mountain was selected as the research area.Methods such as setting up fixed large plot to monitor vegetation dynamics and conducting field vegetation surveys were used to explore the influencing factors of herb expansion.By interpreting vegetation data from permanent plot taken by unmanned aerial vehicle(UVA)in 2017 and 2021,and obtains the spatial distribution and change data of the dominant species at alpine tundra of northern Changbai Mountain which including 10,000 1m × 1m grid.The surface topographic map of the plot was obtained directly by UAV aerial photography.Set soil sampling points every 10 m along the horizontal and vertical directions in the large plot to obtain soil physical and chemical properties at the sample point level,and generate a distribution map of soil physical and chemical properties through spatial interpolation.On this basis,we analyzed the distribution pattern of plant communities and its relationship with environmental factors at alpine tundra of northern Changbai Mountain.We analyzed,the environmental preferences of each dominant species,the changes of dominant species from 2017 to 2021,the effects of environmental factors on the expansion of Sanguisorba stipulata and C.angustifolia.The main conclusions are as follows:(1)Among the six dominant species in the permanent plot,four were shrubs and two were herbs,the native shrubs still occupy the dominant position at alpine tundra of northern Changbai Mountain.According to two-indicator species analysis(TWINSPAN)and field investigation,57 plots were divided into 6 plant communities at alpine tundra of northern Changbai Mountain.Different communities have different species diversity,the species diversity of the communities which have the two expanding herbaceous plants is lower.Through canonical correspondence analysis(CCA),it is found that soil factors were the main factors affecting the distribution of plant communities,and only slope has a significant impact on the distribution of plant communities among the topographic factors.(2)In terms of topography,the two kinds of spreading herbs,S.stipulata and C.angustifolia,were mainly distributed in non shady slope with large slope and roughness.Combined with the field survey found that these places correspond to the valley and other lowlying areas.Low-lying terrain can trap more runoff and soil nutrients,and its longer snow cover will increase soil nitrogen content,providing excellent environmental conditions for the expansion of two herbs.In terms of soil,two expanding herbs were distributed in areas with high soil nitrogen content,phosphorus content and organic carbon content,and low soil potassium content soil p H.Alpine tundra of Changbai Mountain is a typical poor area of nitrogen and phosphorus,lower soil nitrogen and phosphorus levels may limit further expansion of herb.(3)From 2017 to 2021,the percentage of landscape(PLAND),the number of patches(NP),the vegetation coverage and the distribution range of S.stipulata and C.angustifolia increased significantly,indicating that these two herbs are constantly expanding.The contribution of soil factors to the expansion of these two herbs was greater than that of topographic factors.The relative importance of various environmental factors to the expansion of the two herbs was further analyzed,the two factors that had the greatest influence on the expansion of S.stipulata and C.angustifolia were soil total nitrogen content and total phosphorus content.It shows that it has a clear correlation with the expansion of these two herbs.Our research results show that the two expanding herbs are distributed in areas with high total nitrogen and total phosphorus content in the soil,it is further verified that low nitrogen and low phosphorus conditions will limit the expansion of S.stipulata and C.angustifolia.The increase of external nitrogen deposition will alleviate the restriction of low nitrogen conditions at alpine tundra and promote the growth of herbaceous plants.However,soil phosphorus is mainly derived from mineralization of soil parent material,and it is rarely affected by environmental changes.Herbaceous plants are difficult to grow in low-phosphorus areas of the Changbai Mountain tundra,however,shrubs are well tolerant to low phosphorus conditions.Therefore,in the context of increased nitrogen deposition in the future,due to the limitation of phosphorus in soil,it is difficult for herbaceous plants to completely replace native shrubs at alpine tundra of northern Changbai Mountain in the future.