Study On Sexual Regeneration Limitation Of Malus Sieversii Population

Malus sieversii belongs to the genus Malus of Rosaceae.It is mainly distributed in Ili River valley and Tacheng area in Xinjiang.It is the ancestor of M.pumila and is now listed as the second-class endangered plant in China.According to the field observation,it is found that the fruit yield of M.sieversii is large,but the seedlings are rare,and there may be regeneration restrictions.In this thesis,the ecological research methods of seeds and seedlings were used to analyze the limiting factors of sexual regeneration of M.sieversii population from the aspects of seed rain observation,soil seed bank investigation,seed addition experiment and the effects of abiotic factors on seed germination and seedling growth,so as to provide theoretical support for the regeneration and rejuvenation of M.sieversii population.The main results are as follows:(1)The seed rain of M.sieversii began in the middle of July,reached the peak in late August and ended at the end of September,showing a unimodal distribution;M.sieversii seeds are mainly distributed under the crown of the stock tree,and the number of seeds in four directions decreases with the increase of the distance from the stock tree;The number of mature seeds was significantly higher than that of wizened seeds,worm-eaten seeds and rotten seeds.The horizontal distribution of soil seed bank showed that the number of seeds decreased with the increase of the distance from the stock tree;The vertical distribution of soil seed bank showed that the mature seeds were mainly distributed in the litter layer,which was significantly higher than the three soil layers of 0-2 cm,2-5 cm and 5-10 cm;The mature seeds account for24% in the soil seed bank,and the number of seeds is small.The above results of seed rain and soil seed bank showed that the short seed dispersal distance and the small number of mature seeds may lead to the limited sexual regeneration of M.sieversii population.In order to verify the limiting factors restricting the regeneration of M.sieversii population,seed addition experiments were carried out in three habitats.The results showed that the number and percentage of emergence in the sample with 40 and 160 seeds were significantly higher than those without seeds,indicating that there is seed limitations in sexual regeneration of M.sieversii population.The number of seedlings in the forest as occupied habitat increased significantly after adding 40 and 160 seeds,indicating that there is seed source limitation for population regeneration;the number of seedlings in the canopy gap and forest edge as unoccupied habitat increased significantly after adding 40 and 160 seeds,indicating that there is dispersal limitation for population regeneration.The survival rate of seedlings under the E+N(remove vegetation,litter and cover nets to prevent predation)treatment was significantly higher than that of the E(remove vegetation and litter from the ground)and N(cover the nets prevent predation)treatments in the forest habitat,and the seedling biomass of the E and E+N treatments was significantly higher than that of the C(blank control)and N treatments in the canopy gap and forest edge habitat,indicating that there is microhabitat limitations to population regeneration in the three habitat.(2)The seeds of M.sieversii could germinate in the temperature ranges of 25/15 ℃,20/10 ℃,20/5 ℃,15/0 ℃,5/2 ℃;The germination percentage and germination index increased with the increase of temperature,and the initial germination time decreased with the increase of temperature;25/15 ℃ and20/10 ℃ treatments promoted the growth of seedling basal diameter,leaf,seedling height,taproot and biomass accumulation.There was no significant difference in seed germination percentage,germination index and germination initiation time of M.sieversii under different light intensity(P>0.05);The specific leaf area and seedling height increased with the decrease of light intensity,while the basal diameter and leaf number increased with the increase of light intensity;The root,stem and leaf biomass and total biomass of seedlings increased with the increase of light intensity.Under the same precipitation interval treatment,the basal diameter,leaf number and above-ground and under-ground biomass of seedlings increased with the increase of precipitation amount,and the relative growth rate of aboveground,underground and total biomass increased with the increase of precipitation amount;Prolonging the precipitation interval can promote the elongation of taproot and increase the root/shoot ratio.Light,temperature and water had different effects on seed germination and seedling growth of M.sieversii.In summary,the regeneration of M.sieversii population is limited by seed and microhabitat.The main factors limiting its regeneration are short dispersal distance,lack of mature seeds and suitable microhabitat.This paper provides a theoretical basis for the conservation and restoration strategy of M.sieversii population.