A Research On Mechanism Of Widespread Degeneration Of Haloxylon Ammodendron (C.A.Mey.) Bunge In Gurbantunggut Desert

As one of the consequences of the global environment changes,Vegetation degradation has been observed in many parts of the world,especially in arid areas.Located in central Eurasia,the northern part of Xinjiang is typical of temperate inland arid regions.H.ammodendron is the second largest species of perennial shrubby small trees in Gurbantonggut desert,Xinjiang,and is a constructive tree species.It plays an irreplaceable role when it comes to the oasis-soil and conservation of desert ecological sand fixingas well as economic sustainable development of the northern of Tianshan mountain.But the survey finds it has degenerated in large areas in the western part of Gurbantunggut Desert in recent years.There is a serious declining phenomenon for H.ammodendron population in the plains and small sand dunes near plants（height<5m）.It’s growing normally in the big dunes（height>l0m）.There’s a lot of death planning.Limiting the renewal of these groups and groups The growth area is about 40 million square meters.Reasons for degenerate requires exploration and analysis urgently so as to implementate reasonable and scientific measures,and ecological restoration-based on survey of characteristics of degradationH.ammodendron population,climatic factor,soil physical-chemical properties,groundwater level and its qualities and so on,we analyzed the reasons of degenerated H.ammodendron population in Western Gampengut desert.At the same time,studies were conducted on the degraded plains and small sand dune habitats of H.ammodendron forest,comparing the well-grown large habitats of sand dune,for the characteristics of H.ammodendron population,and comparing the seedling survival and seed germination of H.ammodendron group in the chemical and physical soil characteristics of the three habitats.The comprehensive analysis of small sand dunes and large sand dunes is carried out.We have summarized its current situations and Causes of degradation of H.ammodendron population in Gebandungute.The results are as follows:（1）These species composition of the communities is monotonous and only H.ammodendron population were found in most of the plots.In the study area,11.58 per cent,which is a huge decline.The average coverage rate for the rural population is 25 per cent compared to the average coverage rate of 25 per cent early 1980s.The lower seedling density and inverted pyramid type of the age structure indicated:the H.ammodendron population was declining in degradation area.In addition,the plots were divided into low plain（also called soil plain）and small dune（tempered ups and downs sand dune）and big dune（height>l0m）by different habitats.The H.ammodendron population suffered the degeneration and the death massively in low plain and small sand dunes,on the contrary,the H.ammodendron grow well in big sand dunes.（2）Dead plant in 16 countries,the distribution of H.ammodendron groups is significant20 observations,indicating it’s not decrease in internal species（normal death）,and it was abnormal death.There were dead plants in H.ammodendron population of all ages,which indicated that there’s no relationship between plant age and aging.It is my honor to study that the annual precipitation in the study area has not differed significantly over the past twentyyears..,while there is an increasing trend in the average annual temperature and potential evaporation,which indicates that precipitation is limited impact for H.ammodendron population.100 seeds,weight with fin perianth,the relationship between diameter and the weight of 100 seeds in three habitats,the nged perianth is distinctly different.（plain,small sand dunes and big sand dunes）.H.ammodendron population seed germination rate is not obvious.The non-salt stress conditions were different and decreased with the increase of salt concentration,but the decrease of seed germination rate in normal regions was more significant,The results show that seed characteristics of H.ammodendron population on the regenerating effect of H.ammodendron population is limited.（3）The survival index and coverage of H.ammodendron population were significantly（P<0.05）or extremely significantly negative（P<0.01）correlated with groundwater level（r=-0.63,P=0.007;r=-0.68,P=0.004）.In other words,with way the water table rises,the way it survives index and coverage have decreased significantly.We believe that the groundwater depth is very important for the H.ammodendron population growth or survival.Both the depth of groundwater and the high concentration of salt in groundwater have an impact on the use of groundwater of H.ammodendron population.The conductivity of plains and small sand dunes is much greater than the large sand dunes where they normally grow,and the grass population is severely degraded.The number of lateral roots in the degraded area 0-90cm depth is small,and it is difficult for soil water to penetrate.The results showed that the high conductivity of soil in the study area seriously affected the growth of plants for H.ammodendron population,the slow infiltration of soil water and the high salinity of the soil,which limits the distribution of lateral roots of H.ammodendron population.（4）Most of the soil in the study area is severe salinization soil or extremely severe salinization soil.The surface soil shows severe salinization,which is obvious salt crust.It is negative correlation between the individual viability significantly of H.ammodendron population and surface（0⁴0cm）and intermediate（40⁸0cm）soil conductivity（r=-0.79,P=0.00000,r=-0.32,P=0.009）,they are also a very positive correlation between population growth and very low（80¹20 cm）soil water（r=0.54,P<0.01）.Soil organic matter,CL^-,S0₄^2-,the relationship between pH value and individual viabilityof H.ammodendron population is not significant is that all physical and chemical factors may affect the growth of plants together.The research reveals that the species richness in the region is not directly connected with the underground water level,but negatively correlated with soil conductivity.The research also suggests that groundwater level has no significant effect on the survival of H.ammodendron population seedling.However,there exists a significantly positive correlation between the mortality rate of H.ammodendron population seedling and soil conductivity.Salt deposition in surface soil leads to a physiological water shortage of H.ammodendron population seedlings,thus influencing the regeneration of H.ammodendron population.It is a obviously negative relationship（r=-0.61,P<0.01）between soil（0-30cm）electrical conductivity and the H.ammodendron numbers of height<40cm,the results showed that the high soil salt accumulation in the study area seriously affected the survival rate of H.ammodendron population seedling.（5）Quantitative analysis of the contribution of groundwater,soil and climate to the decline of H.ammodendron:groundwater（water level decline and water quality variation）、（soil salification and the lower available soil water content）and climate（rainfall and temperature change）three influence factors,soil factors of has the greatest effect in the degradation of H.ammodendron decay,groundwater factors is the second,climate factors is minimal.Groundwater,soil and climate contributed to the degradation of H.ammodendron decay for 37.44%,49.17%and 13.39%respectively.