Studies On Endangered Mechanism And Population Conservation Of Abies Ziyuanensis

Abies ziyuanensis is a newly discovered species.It was identified as the endangerous species in "Treasure and endangerous plants for protection in China"(volumⅠ),and was listed as the national first-grade protection plant in National Wild Plants List for Protection (Ⅰ).However,till to now systematic and comprehensive research on the plant has not yet been conducted and reported,in terms of all the reporters and research papers published. So in this paper,by means of field experiment,sample plots investigation,location observation,and date analysis,endangered mechanism and population conservation were studies based on aspects of Geographic Distribution,Eco-environment,Morphological anatomy,growth pattern,biological and ecological traits,population ecology,and Genetic differentiation and other factors.The results showed as followings.Studies on endangered mechanism and population conservation of Abies ziyuanensis.1 Climatic changes is the main cause leading to endangered of the species.In Mingzhu Lao shang,Daoyuan and Du Pan Lin,the distribution of Abies ziyuanensis shows latitudinal intermittence joint pattern,which distributes on the North side of Nanlin,and the area becomes a suitable reproduction place,when the species transfer toward north.If temperature continues to keep rising,the Abies ziyuanensis community will be replaced by other hardwood species.2 The Abies ziyuanensis distributed starrily and isolated.Since the environmental changes and geographic isolation,the species only exist in some habitats and formed isolated distribution,which resulted in community differentitation.Investigation on different populations in Hunan province indicated the differentiation,such as Abies in Duyuan was quite different from the Abies ziyuanence in Morphological anatomy,so that was named as new species,Abiese dayuanence3 Abiese ziyuanensis was a Abiese species of geographic substituted distribution of extending towards to South-east.The species differentiated into different relative species gradually,which formed geographic substituted distribution at horizontal or vertical direction.However,at some area,its distribution was overlap,which developed different evolution process and ecological traits among different species.Abies beshanzuensis,A. ziyuanensis and A.yuanbaoensis were closely affinity in systematic development,which suggested that the three species developed from the same ancient.4.Abiese ziyuanensis was sensitive to temperature change.Temperature affected growth and development of A.ziyuangensis directly,besides the factors such as rainfall, moist and sunlight that affect its growth rate.When daily average temperature is over 8.4℃,Sap flowing starts.And buds enlarge required temperature of 13℃daily average, optimist temperature for growth was about 16-19℃,and the temperature difference between day and night is about 8-10℃.When monthly average temperature was over 20℃, the tall growth slowed down or stopped completely.Growth time of A.ziyuanensis was short,about 80 days in whole year.During May and June,the species grew fast,and from later June to the early July,its tall growth slowed down,and stopped growing at the later July.5 Abiese was hermaphroditic and monoecious.Usually,the male flower distributed on the middle and top crown to shade side,a fewer male flower grew at the low part of the tree,Female flower were very fewer and grew on the branches closing to main stem or stronger branches(three to five round branches),which affected the seeds production significantly.About 10 days after pollen,young and green cone developed.The species has low yield of seeds,and only 5.9%seeds were qualified.6.The germination rate of A.ziyuanensis seeds was very low,about 2-4%.The seeds needed to be stratified at low temperature for about 1 month,to break dormancy,before germination.Constant temperature of 25℃and enough sunlight were favorable to germination.Requirement for sunlight between seedlings and young trees was different, young trees needed much more sunlight than seedlings did.Compared with young trees growing at open area or under big tree,young trees growing under shade grew much faster with bigger base diameter,However the difference was not as obvious as that for seedlings. Young trees growing fast required enough sunlight,in contrast,difference resulted from other environmental factors were little.7.A.ziyuanensis community generally has three types:①Abies ziyuanensis,Cyclobalanopsis stewardiana and C.mutinervis community;②Abies ziyuanensis and Fagus lucida community;③Abies ziyuanensis,Phyllostachys pubesoens and Schima argentea community.All the communities characterized with that mixed with ancient species(tertiary or more primeval genera),mixed with warm species(lot of warm-like hardwood species invade) and Abiese species became the sub-species;mixed with hardwood species,for the evergreen broad-leaved tree of fagaceae species naturally regenerated well,and was stable,the A.ziyuanensis become the accompany species.8 There was great difference of age among different population.There were fewer existing young trees,and trees became aging more and more serious.The trend of death of A.ziyuanensis within 180 years old was as followings:trees of age 0 to 30 has lower death rate,only 0.224;age 30 to 50 and 50 to 70 the death rate increased up to 0.675 and 0.673 respectively.Plant at the age of 70 to 90 was at mature period,and death rate decreased in contrast with plant at age of 30 to 70;90 to 110 years old tree has low death risk;110 to 130 years old tree,the physiological activity became weak,and at the highest risk of death; 130 to 150 years old tree had stronger resistance,the death rate decreased to 0.444Climax of life expectancy was at the age of 90 to 110,it had high living quality and vigor physiological activities;also trees at age of 0 to 30 had higher life expectancy,for the trees regenerating on the forest gap had little competition pressure at this period;at the age 110 to 130 or over 130,the average life expectancy of A.ziyuanensis decreased sharply, which was less than 50%of that for 90 to 110 years old tree,and reflected the decay of the population.9 The population distribution formed clumped pattern.Clumped distribution existed in different population structure,the gathering index was high;there were lot of contagious distribution,forest gap formed uneven-aged population,competition of ecological niche in upper space was strong.Radom distribution occurred in vigorously growing stage,and in the communities with high resistant to natural disaster;Sunlight was the main factor that affected the development of plant,then affected the distribution pattern.10 Natrual population had high genetic diversity.The proportion of polymorphic loci in the natural population was 77.78%,and the proportion of polymorphic loci of A. dayuanensis and A.ziyuanensis populations was 50.54%and 40.34%respectively.The Nei's index of genetic diversity was 0.2344,Shannon information index was 0.3764.In terms of the proportion of polymorphic loci,genetic diversity of A dayuanensis was higher than that of A.ziyuanensis.For the A dayuanensis,population located at Xianggupeng had highest genetic diversity,while population at Xunhuan Mountain had lowest diversity. Based on other index,the analysis results was the same,that was A.dayuanensis had higher genetic diversity than A ziyuanensis.11 Genetic differentiation of Natural A.ziyuanensis population.The total gene diversity H_t=0.2346,the gene diversity within population was 0.146,which suggested that the gene diversity within population was higher than that of inter populations.The genetic differentiation index(G_st) was 0.3779,that meant 37.79%of gene diversity contributed by interpopulation and 62.21%contributed by intrapopulation.The results also indicated that, genetic differentiation existed among different populations to some extend,but most genetic differentiation came from intrapopulation.Shannon information index of interpopulation was 39.68%,and index of intrapopulation was up to 60.34%,which also indicated that most genetic differentiation came from intrapopulantion12 Nei's genetic distance.UPMGA cluster analysis on 6 populations indicated that 4 population of A dayuanensis was classfied into a group,and 2 A ziyuanensis population clusted into a group,cluster analysis on both indiviual and population indicated that genetic differentiation existed between the populations of the two species,which confirmed that the two was isolated differentated into two species.13 Index of genetic differentiation(G_st) was 0.3779 in this paper,which was little higher than the average index(G_st=0.34) published by Nybom(in 2004) by means of ISSR analysis.The results indicated genetic differentiation existed in natural population, interpopulation maybe formed heterogeneous population structure.The gene flow(Nm) of A ziyuanensis was 0.6231,that suggested great genetic drift had happened in its evolution process,however the gene flow was blocked between different population,which resulted in populaiotn differentiation.Decrease of population size resulted in genetic drift,and weakened the adaption of population,then evolution capacity declined,which lead to be endangerous.14 Endangered A ziyuanensis was caused by the interaction of interior and exterior factors.The exerrior included climatic change,human beings' activity and environment of population,the interrior factors included flowing,fruit,seeds germination and competition ability of seedlings.15.Measures for allevating endanger.To enforce the research on sexual propagation and vegetation propagation of A ziyuanensis,overcome the technical difficulty,so as to relize the insit and exit protection,also provide seedlings for afforestation.Do some reasonable activities,such as conduct thin on hardwood species and banboom,keep the crown close between 0.4 to 0.5.also conduct tending on the vegetation under the forest,so as to enhace natural regenation,to increase the number of population.Great attention should be put on the protection of ecological environment,to stop destroying forest,and to protect habitates of endangered plants.