Natural Regeneration Mechanism Of Endangered Plant Davidia Involucrate

Davidia involucrata,one of the endangered and conserved plants in China,is facing with the dilemma of the population regeneration.However,it remained to be determined whether propagation(sexual vs.asexual),seed traits(seed set,seed rain,seed dispersal,seed bank),seedling establishment are associated with population regeneration.Here I conducted the field and lab experiments to examine how this variation in propagation(sexual vs.asexual),seed traits(seed set,seed rain,seed dispersal,seed bank),seedling establishment,and sprouts(stump vs.stem basal)impacted population regeneration in this endangered species.The main results are shown as follows.(1)Davidia involucrata is a dominate species in community associated with many rare and endangered plants.The age structure of D.involucrata population presents a declining structure of “inverted Pyramid”(i.e.most of them is old individual).The seedlings of D.involucrata is competed with other species in community,especially to the shrubs and herbs.(2)The variations in seed yeild of D.involucrata was found between indivudla trees,but seldom in interannual variations in terms of population.In this study,there is higher seed yield during the expermential period.The spatial pattern of seed yiled likes the Christmas tree.That is to say,seeds are always found on the outsite crown in the trrees.The furits of D.involucrata is big and elliptical,with the thick fruit flesh.There are many(1-5)kernels in the one drupe(For the needs of research,we call it seeds).(3)The dispersal of D.involucrata seeds is not very far from maternal tree,and it is found 84% of seeds concentrated within the range of 0-5m under the crown diameter of the mother tree,whereas 34% of seeds after nibbleing by animals(both for fruits and seeds)were dispered outside the range of 5m under the crown.The average magnitude of seed rain is 14.4 seed per square meter,and the duration of seed rain is about 60 d.Seeds dispersal in lower altitudes is earlier than the that in higher altitudes.(4)Seed number,seed vitality and seed germination decreased with the temporal dynamic of seed bank.There is high seed vitality within 6 months as seeds falling to the seed bank.In the soil seed bank,seeds were centered at 3 cm from the above-ground to under-ground.Seeds that are buried between 0-3 cm soil layer have highest vitality(averaged by 64.2% of germination seeds),whereas low seed germination was found in seeds under natural conditions(averaged by 19.0% of germination seeds).The germination rate of seeds that keep on the canopy and selected before sowing were higher than that of seeds from the soil seed bank.In addition,variations in seed germination was found in differential place.Compared to the seeds under the canopy or in the ravine,the germination rate under the GAP were the highest.Moreover,much more seedlings were found when seeds buried at 0-3 cm of soil layer.Affected by adverse environmental factors,pests and diseases,97.2% of Seedlings are died.The regeneration range were found within 5 m distance from the maternal plant.(5)There are two types of seedling in D.involucrata(i.e.sprouts vs.seedlings;the ratios of sprouts to seedlings is 1.24).Under nature conditions,more than 1/4 maternal plant can produce sprouts.Interesting,there is positive relationship between sprouts number and height or crown diameter of maternal plant.The shape of age structure of seedlings is fusiform.However,there is age class complementation between sprouts and seedlings in the population.Moreover,the number and height in sprouts are higher than that of seedlings,but the number of branches per year,the growth of the height and the diameter at breast height are lower than those of seedlings.It is also found there is the positive relationships between the number of seedling branches and temperature,humidity,illumination,herbaceous layer and litter layer.Meanwhile,the positive relationship between the number of branches and soil moisture is found in sprouts.In addition,the growth rate of branches in seedlings is related with illumination and soil moisture,whereas the growth rate of branches in sprouts is related with illumination,humidity and soil moisture.The diameter at breast height(DBH)of seedlings is correlated to the humus layer,the growth rate of the DBH is related with temperature,humidity and illumination,plant height is correlated to the herbaceous layer and litter layer.In conclusion,seed germination and seedling establishment determine to the natural regeneration of D.involucrata population.Meanwhile,sexual propagation and asexual propagation co-maintain the natural regeneration of D.involucrata.population.The study reveals the natural regeneration mechanism and endangered factors of D.involucrata,and provides theoretical and practice guidance for scientific conservation strategy and population recovery research.