Spatial Heterogeneity Of The Remnant Myricaria Laxiflora Population In Sexual Reproduction

Myricaria laxiflora is a perennial shrub in the genus Myricaria in the family Tamariaceae,which has lost all habitats in the original reservoir area due to the construction of the Three Gorges Dam and is endangered.The construction of the Three Gorges Dam has caused changes in the water level downstream,and has brought the habitat to flood earlier in summer and delayed exposure in autumn.In this paper,the community structure,flowering and fruiting traits of Cypress at peak flowering and fruiting in normal climate,the number of leaves and survival of plants in abnormal climate,and the changes along the gradient of flowering and fruiting traits at peak flowering and fruit blooming in normal climate were studied by taking the residual population of Cypress in Guanzhou Island of Zhijiang River as the research object,so as to reveal the spatial heterogeneity of sexual reproduction of the remaining population.At the same time,the relationship between the spatial variation of sexual reproduction and environmental factors in the remaining population was analyzed,and its effect on the sexual reproduction of the residual population of Cypress officinalis was studied.The results are as follows:(1)The distribution number,crown amplitude and basal diameter of Cypress flora in the habitat of the residual population of Cypress flower-thinned branches showed spatial heterogeneity at different gradients.Among them,the number of flower-thinning cypress branches in the lower swelling zone was higher than that in the upper swelling zone and the middle swelling zone.The crown amplitude and basal diameter of the upper swelling zone were higher than those in the middle and lower swelling zones.The herbaceous layer of the plant community showed spatial heterogeneity along the depression gradient,and the number of herbaceous plant species in the lower recession zone was higher than that in the upper and middle rise zones.The physical and chemical properties of soil with different dissipation gradients showed spatial heterogeneity.With the increase of the swelling gradient,the content of total nitrogen and total phosphorus increased,and the content of clay gradually increased,but there was no significant difference between soil p H and organic matter between different swelling gradients.There were significant correlations between the height,basal diameter and crown width of the flower-thinning cypress branches and the number of flowers and fruiting of each plant.There is a significant correlation between soil total nitrogen and total phosphorus.(2)There was spatial heterogeneity in sexual reproduction of remnant populations of Cypress with different swelling gradients.The sexual reproduction of the remaining population in the upper recession zone is better than that in the middle and lower swelling zones.The number of flower branches,the number of flowers per branch,the number of flowers per plant,the number of flowers per plant,the number of fruit branches per branch,the number of fruits per branch,the number of fruits per plant,the number of seeds per fruit and the germination rate of seeds in the upper flowering zone were 66.09%,50.14%,98.63%,60.17%,25.26%,88.05%,6.96% and 30.69% higher than those in the middle flowering zone,respectively.It was 79.50%,283.33%,461.05%,97.39%,82.45%,208.31%,19.12% and45.91% higher than the lower deflating band,respectively.Further correlation analysis showed that there were significant correlations between the number of flowers,fruiting per plant,seeds per fruit and seed germination rate per plant and the altitude gradient,the blooming period,soil water content and temperature caused by it.Therefore,the changes in the ecological environment of downstream habitats caused by the regulation of river water level fluctuation rhythm by dams will have an impact on the sexual reproduction of the remaining population.(3)There was some spatial heterogeneity in the wind propagation of Cypress flower-thinning and seed density in soil seed banks in different decline zones.The seed density of wind propagation in the upper recession zone and the thinning water cypress branch in the soil seed bank were higher than in the middle and lower recession zones.There was also some spatial heterogeneity in the density of herbaceous seeds in soil seed banks of Cypress flora flora plant communities in different decline zones.The seed density of herbaceous plants in the soil seed bank in the lower recession zone was higher than that in the upper recession zone and the middle recession zone.There was a significant correlation between wind-borne floral cypress branch density and flowering per plant,and between the number of fruits per plant.There was a significant correlation between the density of flowers and trees in soil seed banks and the number of flowers and fruiting per plant.(4)The abnormal climate has a significant impact on the growth and flowering and fruiting of plants in the population of Cypress officinalis.In the peak flowering period,the average number of flowers per plant,the average number of flowers per branch and the average number of flowers per plant decreased by 27.56%,69.12% and 75.26% respectively compared with the normal climate period.In the peak fruit period,the average number of fruit branches,average fruit per branch,average number of fruit per plant,average number of seeds per fruit and average seed germination rate of the abnormal climate period of Cypress flowers decreased by 17.88%,55.25%,62.25%,1.15% and 1.61%,respectively.However,under the influence of abnormal climate,the growth of plants with different swelling gradients still showed a certain spatial heterogeneity.The survival rate of plants in the upper and middle recession zones was higher than that in the lower swelling zone.The number of blades and the reduction rate of blades in the upper swelling zone were higher than those in the middle and lower swelling zones.There is also spatial heterogeneity in the sexual reproduction of the residual populations of cypress branches with different abnormal climates.The number of flowers per branch,the number of flowers per branch and the number of flowers per plant in the upper swelling zone were 50.12%,78.73% and 161.12% higher than those in the middle swelling zone,and 88.11%,121.20% and 318.03% higher than those in the lower swelling zone,respectively.The number of fruit branches,fruit per branch,fruit per plant,seed number per fruit and seed germination rate in the upper swelling zone were 45.07%,25.32%,63.63%,13.44% and 20.60% higher than those in the middle swelling zone,respectively.It was79.57%,78.93%,199.44%,24.84% and 48.56% higher than the lower deflating band,respectively.Further correlation analysis showed that the number of flowers,fruiting per plant,seeds per fruit and seed germination rate were significantly correlated with the altitude gradient,the blooming period,soil water content and temperature caused by it.Therefore,under abnormal climatic conditions,the impact of dams on downstream water level regulation on the sexual reproduction of residual populations is more serious.