Effects Of Permafrost Active Layer On Growth And Understory Vegetation Of Larix Gmelinii In Cold Temperate Zone

The Greater Khingan Mountains is the main distribution area of high-latitude permafrost in my country,and its ecological conditions are fragile,highly sensitive,and vulnerable to environmental and climate changes.Larix gmelinii is the main forest tree species in the The Greater Khingan Mountains.Together with the permafrost of the The Greater Khingan Mountains,it constitutes a cold and humid environment in this area.This cold and wet environment maintains the growth of Larix gmelinii,and the existence of permafrost active layers It is a comprehensive reflection of the cold and wet environment of the The Greater Khingan Mountains.Therefore,this thessis takes the Larix gmelinii forest in the permafrost region of the The Greater Khingan Mountains as the research object:(1)to explore the effects of different active layers(2m,1m,0.5m and control)on the growth,regeneration and understory shrub and grass of Larix gmelinii;(2)Combined with the research results of aboveground plant growth and underground soil temperature,the main factors affecting the growth of Larix gmelinii were determined,which could provide a basis for the dependence of the growth of Larix gmelinii on the existence of frozen soil.The main findings are as follows:(1)The permafrost temperature changed significantly with the seasonal change of the Greater Khingan Mountains(p<0.05).The freezing time of different permafrost active layer thicknesses all started in September,but there were significant differences in the thawing time in the coming year,and the time of freezing and thawing during the period was significantly different.It also increases with the increase of the active layer,and presents0.5m(122d)<1m(153d)<2m(214d);the contents of soil organic matter,total nitrogen and total phosphorus in different permafrost active layers also increase with the increase of the active layer increased(0.5m <1m <2m < control),while the total potassium content showed the opposite trend.(2)With the increase of permafrost active layer,the growth trend of diameter at breast height,tree height and biomass of Larix gmelinii showed the best growth trend in the control plot,followed by 2m active layer,0.5m active layer grew the slowest,In addition,the growth differences of Larix gmelinii between different active layers were significant except for biomass(p<0.05).The carbon storage advanced growth and carbon storage loss of the forest stand showed opposite trends,that is,the thicker the permafrost active layer,the greater the advanced carbon storage of vegetation,and the smaller the carbon storage loss.(3)There were significant differences in the ground diameter,tree height,crown width and biomass indexes of the renewed seedlings between the control plot and the 0.5m permafrost active layer plot(p<0.05).The specific performance is as follows: on different permafrost active layers,the growth law of the ground diameter and crown width of the regenerated seedlings is control >2m >1m >0.5m,and the regenerated seedlings in the 2m active layer are taller than control in the 2cm diameter step,and in 2cm and 2cm the biomass in the 5cm diameter stage was greater than that in the control.(4)The species composition of herb layer and shrub layer increased with the increase of permafrost active layer,but the species of shrub layer and herb layer were different in different permafrost active layer.The performance is as follows: the relative density of Carex spp is the highest in the herb layer of the active layer plot in the frozen soil area,while the relative density of Pyrola calliantha in the herb layer of the control plot is the highest;1m and 2m active layers have the highest relative densities of Betula fruticosa,Ledum palustre and Vaccinium uliginosum,respectively.Redundancy analysis showed that among the five soil factors screened out,the thickness of permafrost active layer,ground temperature and soil organic matter were positively correlated with the biomass of Larix gmelinii and the biomass of understory shrubs and grasses.It can be seen from the ranking of organic matter that the influence of organic matter is small,but the influence of the thickness of the active layer of permafrost and ground temperature is more obvious.