Fine-scale Spatial Genetic Structure Analysis Of An Endangered Plant Tetracentron Sinense Oliv.in Leigong Mountain

Spatial genetic structure?SGS?was used to explore the interaction among plants as well as between plants and their habitats.Knowledge of SGS was of important significance for evaluating the development potential and evolutionary direction of endangered plant nature populations.However,the major influencing factor in the formation of fine-scale SGS is the restricted gene flow.In this thesis,we took the wild Tetracentron sinense Oliv.population in Leigong Mountain natural reserve as the research object,and used 15 pairs of microsatellite?SSR?primers to assess SGS and the extent of gene dispersal,and then evaluated the evolutionary potential of T.sinense in this reserve and revealed its endangered mechanism,which can help to provide scientific basis for effective conservation and management of the endangered plant.The main results are as follows:?1?Genetic diversityThe number of alleles?A?,effective number of alleles?A_E?,observed heterozygosity?H_O?and expected heterozygosity?H_E?of T.sinense were 4.067,2.769,0.483,0.598 at the species level,and 3.667,2.498,0.487,0.564 at the patch level,respectively.The genetic diversity of T.sinense was moderate comparing other endangered species.Different genetic diversity and significant genetic differentiation(F_st=0.071?0.098)were detected among the four patches.The variance within patches was the main source of the genetic variation for T.sinense at a fine spatial scale.Genetic variation of the cohort was largely affected by microhabitats.Roads and uplift mountain ridges may contribute to the blocking of gene dispersal between patches.?2?Fine-scale spatial genetic structureA significant spatial genetic structure was detected within 400 m in this reserve,and the Sp value was 0.0305,indicating a higher level of SGS among endangered trees.In addition,due to the significant genetic differentiation between patches,the coefficient of individuals decreased from a significant positive correlation to a significant negative correlation at the distance of 400 m?500 m.Analysis of different age-classe of T.sinense in this reserve showed that the Sp value of young trees,adult trees and old trees were 0.0224,0.0407 and 0.0640 respectively.An increase in SGS was found with the increase of age-class.Sp of old trees was 3times as high as young trees,which may be correlated to a higher seedling mortality rate of young trees and the overlapping generation of old trees.The results showed a negative influence of selfing decline of T.sinense in this reserve.Positive correlation of SGS was detected in four patches.Among them,significant SGS was found in HP and 89G at the distance of 20m and 15m separately,with the intensities of 0.391 and 0.193 respectively;weak SGS with the intensities of 0.0184 and0.0109 were found in 14G and 12G,respectively.The order of Sp of four patches from large to small was HP>89G>14G>12G.?3?Gene flowGene flow analysis showed that a greatly limited distance of gene dispersal of T.sinense was found in Leigong Mountain.Indirect estimation by GenAlEx 6.505software showed that the effective distances of gene dispersal in 14G,HP,12G and 89G were 70.37 m,21.62 m,24.68 m and 57 m respectively.The distance of gene dispersal decreased with the increase of effective density of T.sinense population estimated by SPAGeDi 1.3 software.In addition,parentage analysis of young trees indicated that the distance of gene dispersal was 29.22?38.69 m,the farthest distance of pollen and seed dispersal was 159.88 m?mean 53.17 m?,86.84m?mean 24.99 m?respectively.Local climate,vegetation density,physiological characteristics of T.sinense and habitat topography had great impact on the dispersal of gene flow.In summary,T.sinense population in Leigong Mountain was at a risk of inbreeding decline,and the limited distance of gene dispersal will increase the accumulation of this risk.The spatial range of genetic structure was 20 m,indicating a intimate relationship among individuals in this range.Therefore,the interval of individuals sampled should be more than 20 m apart to ensure that the collected individuals included most of the genetic variation in the area for ex-situ conservation,and cross-breeding at different patches could be applied in in-situ conservation.Additionally,moderate human disturbance should be used to increase the survival rate of seedlings.