Soil Environmental Effects Of Different Ground Cover And Their On The Physiological And Ecological Characteristics Of Populus Euphratica Seedlings

Populus euphratica Oliv,as an important part of oasis vegetation in arid areas,is the basis of a strong ecological barrier and biological community in the area,which is closely related to the rise and fall of oasis.In recent years,the Populus euphratica forests along the Tarim River have been seriously degraded,mainly due to the single and limited number of regeneration methods for Populus euphratica seedlings.In view of this,This experiment used 1-year-old Populus euphratica seedlings in Bazhou nursery as test materials from April to September 2018,by studying the spatio-temporal distribution of soil moisture,temperature and electrical conductivity of different ground cover（covered with hydromulching,straw mat and fine sand）and periodic change law,and determine the response characteristics of seedling photosynthesis physiology and growth to cover effect,using membership function value method and gray correlation method to synthesize different surface cover based on 23 indicators such as soil,photosynthesis and growth evaluation to determine the most suitable cover measures for seedling growth,with a view to providing scientific reference for the cultivation and protection of Populus euphratica seedlings and field regeneration.The research results are as follows:Under the mulching conditions,in terms of soil layer,the soil moisture,temperature and conductivity of the 0-40 cm soil layer are significantly greater than those of the 40-80 cm soil layer.After the conductivity change was significantly greater than that of irrigation for 2 days,the water retention effect was prominent.On the whole,the volumetric water content of the hydromulching,straw mat and fine sand increased by 15.7%,20.7%and 7.5%compared to the bare soil,the soil temperature increased by 1.4%,-2.62%and 0.28%,and the soil electrical conductivity decreased（Soil desalination rate）21.6%,24.6%and 14.7%.The variation of the three soil parameters of straw mat is small,and the effect of cooling and water retention is obvious at high temperature,and the soil environment is the most stable.Under the covering condition,the daily change curve of leaf photosynthesis showed a"single peak"curve,which enhanced the seedlings’utilization efficiency of midday light energy,and the relative content of leaf chlorophyll（SPAD value）,net photosynthetic rate（Pn）,stomatal conductance（Gs）,Transpiration rate（Tr）and water use efficiency（WUE）have been significantly improved,and their daily average values are:straw mat>hydromulching>fine sand>bare land,there is no significant difference between straw mat and hydromulching（P<0.05）,among which the average daily SPAD value of straw mat was increased by 2.6%⁹.86%compared with other treatments,Pn increased by 2.78%³1.72%,and WUE increased by0.85%¹3.67%.The maximum net photosynthetic rate(P_nmax)and light saturation point（LSP）of hydromulching is second only to straw mat,but the light compensation point（LCP）,dark respiration rate（R_d）and photorespiration rate（R_p）are large.The apparent quantum efficiency（AQY）and R_d of fine sand are small,the CO₂ saturation point(C_isat)and CO₂ compensation point（Γ）are large,but their photosynthetic potential is not large.The P_nmax,LSP and maximum Rubisco anteversion efficiency(V_cmax)of straw mat were the largest,and V_cmax was significantly increased by 18.9%⁴7.93%.Under the condition of coverage,the survival rate of seedlings,plant height,ground diameter,biomass growth and root-shoot ratio were all increased significantly.Compared with the control,the survival rate of seedlings of hydromulching,straw mat and fine sand increased by 17.46%,16.02%and 10.38%,respectively,biomass increased by 84.48%,87.45%and 64.08%,and the root-shoot ratio increased by13.48%,15.73%and 11.23%.Based on the 23 indicators observed in this study,it was found that the order of the best effect of different ground cover on the growth of Populus euphratica seedlings was:straw mat>hydromulching>fine sand>bare ground.It is suggested that grass seed can be used as one of the effective measures to promote vegetation restoration at the early stage of Populus euphratica forestation（seedling stage）,which is consistent with the principle of sustainable development of Populus euphratica seedling growth and efficient water use in the study area.