| Physocarpus amurensis,only deciduous shrub of the Physocarpus(Rosaceae)in China,was an ancient relic species.The population number and distribution range of this species were dwindling,had been listed as rare and endangered plants of the second batch of China.The species had important ornamental value,medicinal value and ecological value,and had an important the significance for carrying out the research of protection and silviculture.The protection and development utilization of P.amurensis were restricted,and the main reasons were the lack of comprehensive understanding concerning current situation and future development trend of population,the level of genetic diversity of population and the adaptability of the main ecological factors.In this study,we knew the internal control factors of limiting population expansion through the study of population structure and genetic diversity,and provided a theoretical basis for the protection and recovery of population of P.amurensis resources.We knew its ecological adaptability through the study of plasticity response ability of morphological structure and physiological aspects on the seedlings in the changing light environment,water environment and nutrient environment.It provided theoretical guidance for artificial cultivation measures such as ex situ conservation,introduction cultivation,and further to provides basis for excavate and utilize the application value of the plant resources.The main results were as follows:1.The seedlings were deficiency in P.amurensis population,and there were more individuals in middle and old age.The survival curve of the population appeared to be the Deevey-Ⅱ type.The trend of the change of mortality rate and vanishing rate curves of population was basically the same.The individual mortality rate of different age class was very high,and the population showed a sustained sharp decline.The population survival rate function curve decreased monotonically,whereas the cumulative mortality rate function curve increased monotonically,the decreased or increased range being higher at early stage than at late stage.The death density function curve was relatively stable,with a higher rate during the V age class.The hazard rate function curve was gradually increased with the growth of age class.The deficiency of seedlings could be the main reasons leading to the P.amurensis population becoming depression.2.The optimal PCR system for ISSR analysis was 3.0 mmol-L-1MgCl2,0.15 mmol-L-1dNTPs,0.5 μmol-L-1 primer,1.0 U-μL-1 Taq polymerase,1.0 ng-μL-1 DNA template,and 2.0 μpL PCR buffer(10x)in 20 μL reaction solution,and the augmentation procedure was pre-denaturation at 94℃ for 5 min,denaturation at 94℃ for 35 s,annealing at 55.5℃ for 45 s,extension at 72℃ for 90 s,reaction with 35 cycles,and extension at 72℃ for 10 min.The genetic diversity of 48 individuals from 4 aggragations was analyzed using this system.ISSR amplification was conducted with 13 primers,and 31 polymorphic loci were detected from 88 clear DNA fragments.The genetic diversity was relatively low both the species level and aggragations level.The percentage of polymorphic bands(PPB)was 35.2%,Nei’s gene diversity(H)was 0.1304,Shannon information index(I)was 0.1916 at the species level,and PPB was 24.2%,H was 0.0889,I was 0.1321 at the aggragations level.A limited gene flow(Nm=.2185)resulted in a high genetic differentiation(Gst =0.2909)among aggragations.A mantel test showed there was a significantly correlation between genetic distance and geographic distance among the aggragations(r=0.882,P＜0.05).With UPGMA dendrogram,4 aggragations were separated into two clusters at the specify threshold of 0.01.The habitat fragmentation and barriers of gene flow were an important factor for a highly genetic variation among aggragations and the low genetic diversity within aggragations.3.P.amurensis was heliophilous trees,and very sensitive to changes of the light environment.The height growth of seedlings was promoted in L1 and inhibited in L2.The shading had resulted in significant increase crown width(P＜0.05),and significant decrease basal diameter,and leaf number(P＜0.05).The shading had resulted in significant decrease the biomass of root,stem,leaf and plant(P＜0.05),especially L2,decreased by 80.6%,61.1%,70.3%and 71.8%respectively compared to CK.The effect of shading on the collar diameter of first order branch were significant(P＜0.05).The effect of shading on the average length of first order branch,density of first order branch,angle of branch of first order branch,average length of second order branch and density of second order branch were not significant(P＞0.05).The shading had resulted in significant decrease the apparent quantum efficiency(AQY),maximum net photosynthetic rate(Pmax),dark respiration rate(Rd),light compensation point(LCP),light saturation point(LSP)and carotenoid content(Car)(P<0.05),and significant increase chlorophyll a(Chla),chlorophyll b(Chlb),total chlorophyll(Ch1)content and chlorophyll/carotenoid(P＜0.05).The shading had resulted in significant decrease the NSC content of root,stem and leaf(P＜0.05),especially L2,decreased by 52.5%,44.9%and 43.9%respectively compared to CK.P.amurensis seedlings had certain adaptation and adjustment ability to light shading,and the growth was severely inhibited under heavy shading.It should be planted in a sunny environment in production practice.4.The nitrogen fertilization promoted the growth of basal diameter,branch number,crown width and leaf area of seedlings(P＜0.05).The nitrogen fertilization had resulted in significant increased the biomass of stem and plant(P<0.05)and biomass allocation ratio of stem and leaf,and decrease biomass allocation ratio of root.The nitrogen fertilization had resulted in significant increase net photosynthetic rate and leaf nitrogen content(P<0.05).The nitrogen fertilization had resulted in significant decrease soluble sugar and NSC content in root(P＜0.05),and was no significant effect on starch in root(P>0.05).The accumulation of soluble sugar,starch and NSC in stems and leaves was obviously increased.Most of the indexes between nitrogen fertilization treatment(N1,N2 and N3)were not significant difference,indicating that the seedlings of P.amurensis were not sensitive to the change of soil nutrients and the requirements for soil fertility conditions were not high.5.The height and basal diameter increment of seedlings decreased significantly with the intensification of the drought(P＜0.05).The stem biomass,leaf biomass and root to shoot ratio reduced significantly(P＜0.05),and the root biomass and total biomass increased maximum in Wl and then decreased with the intensification of the drought Net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs)and intercellular CO2 concentration(Ci)increased and then decreased,meanwhile,stomatal limitation(Ls)decreased and then increased w with the intensification of the drought,indicating that stomatal limitation was responsible for reduction in Pn.The activities of superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)increased and then decreased with the intensification of the drought,while malondialdehyde(MDA)contents and membrane permeability increased continuously.P.amurensis seedlings were able to adapt to light drought stress(Wl),and the growth and photosynthetic ability of the seedlings were inhibited under moderate and heavy drought stress,and the antioxidant enzyme system was destroyed under moderate and heavy drought stress.Consequently,the endangerment of P.amurensis might be habitat fragmentation and habitat destruction by human activities,which led to the decrease of population number,ageing of population and reduction of genetic diversity.The ex situ conservation should be carried out at the same time to strengthen the protection of habitats,the introduction of artificial species and the restoration of artificial population.It could be cultivated by artificial propagation to realize the conservation of germplasm resources in different places. |
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