The Correlationship Between Permafrost Microenvironment And Vegetation Succession In Upper Reaches Of Heihe

Permafrost is an important part of the cryosphere and a key element to better understand global climate change.The micro-topography of permafrost regions is complex and diverse.The upper reaches of Heihe river,the northeast edge of the Qinghai-Tibet plateau,are characterized by taliks and slump,and the main types of geomorphic types are frozen and expanded grassy hills,shallow pit marshes and hot melt settlement.The changeful micro-topography features result in the environmental differentiation law,which affects the soil water thermal distribution state,physical and chemical characteristics and energy balance in the permafrost regions.The fragmentation of the habitat and the distinct features of this region resulted in the high spatial heterogeneity of vegetation phenological time,community characteristics and functional traits,which was affected by the distribution of permafrost.Therefore,this study analyzed the relationship between the permafrost distribution and phenological characteristics,its trends and factors in the upstream of Heihe.In this study,we observed the effect of slump on the soil environment and recorded the changes of vegetation community in different sliding process,which clarified the influences of slump on carbon flux and the vegetation diversity and the direction of the vegetation succession.The effects of frost heave on vegetation community and functional characters were also analyzed.The main conclusions are as follows:1 The influence of phenology and permafrost distribution in the upper reaches of Heihe river.From 2001 to 2014,if the initial day of engineering soil freezing and biological soil freezing was postponed for one day,the decline period delaies by 0.19 day and 0.32 day,respectively.The growth season is increased by 0.19 days for one day increase in the unfreezing period of the engineering soil.There was an increase of 0.17 day in the growth season for one day increase in the non-freezing period of biological soil.The last frozen day advances for one day for engineering soil freezing and biological soil freezing,while the period of seeding has 0.05 day and 0.09 day ahead.The characteristics of temporal and spatial change in phenology in the upper reaches of Heihe river indicated that the overall period of seeding is in advance,and the overall decline period is also in advance,and the overall growth season is shortened.Analysis of the correlation between plant litters and soil freezing first days displayed that the initial day of soil freezing should use the definition of biological soil freezing,which is best.When we analyze the link between growth season and the soil freezing-thawing index,it showed that the two kinds of calculation results are similar and feasible by using both the biological algorithm and the engineering algorithm.The selection of two algorithms for soil freezing and thawing day need further verified to identify the period of seeding.Terrain is a complex process for vegetation phenology,which is the interaction between the altitude,slope,aspect and vegetation.Topography will influence the local climate,thus,affecting vegetation green period,litter fall period,and phenological period.It is found that the soil freezing-thawing index is more scientific and reasonable in terms of the biological soil freezing in the two regions.The vegetation phenology in the seasonal frozen ground region is more obvious,but the difference of vegetation in two regions is less than 0.3.2 the relationship between slump and micro-environmental vegetation.In the permafrost regions,the thermal slump could affect the redistribution of soil temperature and moisture and change the physicochemical properties of soil.Soil SOC in native vegetation,slump active stage and in stable sliding stage are 5.14 + /-0.48 kg/m3,5.05 + /-0.77 kg/m3 and 4.25 + /-0.63 kg/m3.Compared with the native vegetation stage,slump disturbed soil leading to the SOC reduction(20%).The results show that the thermal slump has a strong influence on SOC loss.In the original vegetation,the TN was about 0.66 or 0.07 kg/m3,and the TN was 0.65 + 0.06 kg/m3 in the active stage of the slump and the stable stage was 0.63 + 0.07 kg/m3.The loss of soil TN affected by the slump was not significant.Compared with species richness,evenness and ecological dominance index,slump will cause succession community,which successes from alpine swamp meadow grassland to alpine grassland.The dominant species in the community changed from cyperaceae and gramineous to gramineous weeds.We studied the correlation between the carbon flux and biodiversity indices through different profiles of permafrost collapse.The result signed that,in the undisturbed samples,the community diversity(HI),the evenness index(EI),and the species richness index(SI)are the main factors controlling the carbon flux.and the dominant species Simpson is diverse.The correlation between the dominant species Simpson and DI can be negligible.In the disturbed samples,HI,EI,SI,and DI are small and shows less correlation with carbon flux when compared to the undisturbed case.Carbon flux is positively correlated with community HI and negatively correlated with EI.But both HI and EI have a significant impact on community carbon balance corresponding to a large correlation coefficient.Meanwhile,carbon flux was positively and poorly correlated with SI and DI.This means that the species diversity of vegetation is not the same,and the dominant species is significantly related to carbon dioxide flux.In the disturbed samples,the carbon flux mainly comes from soil respiration,releasing carbon in permafrost;while in the undisturbed stage,vegetation photosynthesis reduces the carbon concentration in the ecosystem,and the vegetation root maintains low and slows the rate of soil carbon release.3 Relationship among hummock,micro-environment,and vegetationThe micro-topographic of hummock characterized with strong fragmentation,resulting in soil heterogeneity in the micro-environment.In our study,we find that the larger the area of hummock,the more variabilities of surface soil moisture,temperature,and active layer thickness.The correlation between soil moisture and topography is weaker than soil temperature for water saturation;On the top and bottom of the hummock,the thickness of the active layer is similar;the position in the middle is closely related to the active layer and related,and the correlation between slope position and the active layer thickness is less than 0.5.The ratio of leaf mass and leaf number approximately equal to 1 on bottom and the middle of the hummock,showing the relative growth;On the top,the slope was significantly greater than 1(p < 0.05),means the growth rate of leaf mass faster than leaf number growing.With the same theory,the growth rate leaf mass is much higher than leaf area at all position of hummock.The slopes of leaf mass and leaf volume was significantly smaller than 1(p < 0.01),indicating that leaf mass get less material and energy than leaf volume from plant.The bottom of hummock is better than middle and top for Carex to survive and growing,for the heterogenicity of allometric growth is lowest in all relation,including leaf mass and leaf number,leaf mass and leaf area,leaf mass and leaf volume.