Effects Of Different Degrees Of Frozen Soil Degradation On Photosynthetic Products Of Typical Vegetation In The Greater And Lesser Khingan Mountains

The Greater and Lesser Khingan Mountains are located in the southern margin of the permafrost region of the Eurasian continent.It is the second largest permafrost zone in China.It is sensitive to climate change and has poor thermal stability.Global warming and the reduction of vegetation area have led to the degradation of permafrost.At the same time,factors such as human activities have also exacerbated the degree of permafrost degradation.The degradation of frozen soil is mainly manifested in the reduction of the thickness of the frozen soil layer,the reduction of the area of the permafrost region and the increase of the thickness of the active layer et al.The degradation of permafrost leads to changes in the water and heat characteristics of the soil,and the photosynthesis of plants also changes when the external environment changes.The external environmental factors mainly affect plant photosynthetic products by affecting the physiological process of plants.Therefore,the degradation of frozen soil will affect the photosynthetic products of vegetation to a certain extent.Studying the effect of permafrost degradation on plant photosynthetic products is of great significance for maintaining the stability of the ecosystem in the Greater and Lesser Khingan Mountains,and thus provides reference value for wetland protection.This paper takes the Greater and Lesser Khingan Mountains as the research area,and uses remote sensing technology to monitor the permafrost environment.According to the characteristics of the Greater and Lesser Khingan Mountains permafrost,the TTOP model is used to simulate the permafrost distribution of the Greater and Lesser Khingan Mountains with a spatial resolution of 1KM based on the MODIS surface temperature data.The distribution of frozen soil in 2000,2010 and 2020 was analyzed to obtain the degradation of frozen soil,and the temporal and spatial changes of frozen soil degradation are analyzed from multiple climatic factors.In the background of permafrost degradation,in-situ control experiments and field sampling experiments are set up to explore the effects of different permafrost degradation on the photosynthetic products of typical vegetation in the Greater and Lesser Khingan Mountains.Determine the relationship between environmental factors and vegetation photosynthetic products through GEE(generalized estimating equations)and path analysis,respectively.The main results are as follows:(1)The TTOP model divides the permafrost of the Greater and Lesser Khingan Mountains into metastable permafrost,transitional permafrost,and unstable permafrost.The main type of permafrost degradation in the Greater and Lesser Khingan Mountains from 2000 to 2020 is "metastable degradation as transitional type".There are two main types of degradation: "transition type" and "transition type degenerates into unstable type".(2)Under the in-situ control experiment,under low temperature stress,the change trend of photosynthetic products of Carex schmidtii,Vaccinium uliginosum and Betula platyphylla is consistent,as follows: the content of soluble sugar increases,the content of starch decreases,and part of the starch is decomposed into Soluble sugar;the content of soluble protein and free amino acids increases,increases the concentration of cell fluid,and protects vegetation from low temperature damage.(3)The field sampling period is in the late summer and early autumn,with low temperature and high precipitation.The soil temperature in Huzhong and Wuyiling areas decreases and the soil water content increases,and there is a correlation between the soil temperature and the soil water content.The changes of photosynthetic products of Carex schmidtii,Vaccinium uliginosum,Betula platyphylla,Calamagrostis angustifolia,Rhododendron dauricumand Larix gmelinii under low temperature environment are: soluble sugar,soluble protein,free amino acid content increased,starch content decreased.The contents of soluble sugar,soluble protein and free amino acid in Huzhong are generally higher than those in Wuyiling area,while the starch content of vegetation in Huzhong area is obviously lower than that in Wuyiling area.(4)The GEE(generalized estimating equation)is used to analyze the influence factors of photosynthetic products of Carex schmidtii,Vaccinium uliginosum and Betula platyphylla under the in-situ control experiment.The soluble sugar and soluble protein of Carex schmidtii,Vaccinium uliginosum and Betula platyphylla are negatively correlated with soil temperature,and positively correlated with soil water content.There is a positive correlation between starch and soil temperature,and a negative correlation with soil water content.Free amino acids is negatively correlated with soil temperature and positively correlated with soil water content.Path analysis is used to analyze the influencing factors of typical vegetation photosynthetic products in Huzhong and Wuyiling areas.The influencing factors of photosynthetic products in different regions and vegetation are obviously different.However,the thickness of the active layer is the same environmental factor that affects the photosynthetic products of the six vegetations in the Huzhong and Wuyiling areas.The same environmental factors of vegetation photosynthesis further suggest that permafrost degradation affects vegetation photosynthesis.