Studay On Seedling Regeneration Mechanism Of An Endangered Plant Tetracentron Sinense Oliv.

In this paper, the population of Tetracentron sinense Oliv. in the Dafengding Nature reserve of Meigu County, Sichuan Province, were studied. By means of simulating wild natural environment, the controlled seeding experiments were set up by 2 factors 3 levels of light and covering. Seed germination, seedling survival and growth of T. sinense were investigated, and the effects of light and ground cover on seeding recruitment were analyzed. In addition, the spreading mechanism of T. sinense seed was studied, whether there is dispersal limitation on the seedling regeneration was analyzed, and the protection measures were explored. The resuts can contribute to provide some scientific proof for effective protection of T. sinensis and its sustainable utilization. The main results are as follows:1. The effects of light intensity and ground cover on seed germination, survival and seedling growth of endangered plant T. sinensis Oliv.In the seedbed without any cover or with shrub-grass, seed germination rate of T. sinensis was all the highest under 50% light intensity; while there were no obvious differences of seed germination in the seedbed with shrubgrass and litter under any light intensity. The results showed that the seed germination of T. sinensis needed light, but it was not conducive to seed germination when the light was too strong or too weak.The seedling survival rate in all kinds of seedbeds all decreased with the increase of the seedling age, but the mortality rate increased with the increase of seedling age. The survival curves of the seedling showed a downward trend under any conditions, and the variation trend is the most obvious from one month to two month of age. The decline range of survival curve in the seedbed with shrub-grass under 10% or 50% light conditions was all smallest, but that in the seedbed with shrub-grass and litter under 100% light conditions was the biggest. The cumulative Survival of seedling in all kinds of seedbeds decreased monotonously with the increase of the month age, and the accumulated mortality rate of seedling increased monotonously with the increase of the month age, and the variation trend is the most obvious from one month to two month of age. The smallest accumulated survival rate decrease appeared in the seedbed with shrub-grass under 10% or 50% light conditions, and the biggest acccumulated survival rate decrease appeared in the seedbed without any covers under 100% light conditions. The largest increase of accumulated mortality rate appeared in the the seedbed with shrub-grass under 10% or 50% light conditions, and the smallest increase appeared in the seedbed with shrub-grass and litter under 100% light conditions. The results showed that the seedling survival was limited mainly at the second month after seed germination, and strong light intensity were not beneficial to the seedling survival under all kinds of seedbed, and the shrub-grass was beneficial to the seeding survival when the light is not enough.Under the greenhouse, index of seedling survival rate and accumulated survival rate in T. sinensis were all higher than that under no greenhouse, and the seedling mortality, and the accumulated mortality rate were all lower than that under no greenhouse, and its life expectancy was higher than that under no greenhouse universally. the results showed that the erosion of heavy rain in the natural population was one of important factors limiting the seedlings recruitment in T. sinensis.With the decrease of light intensity, height and main root length of T. sinensis seedling in all kinds of seedbed decreased gradually at the same month age, the accumulated value of lateral root number and total dry weight were higher under 10% or 50% light conditions. The results indicated that stronger light can promote the growth of seedling root and stem of T. sinensis, but will inhibit the growth of lateral roots and biomass accumulation, and the moderate shade is necessary for seedling growth of T. sinensis. At different month age, the increase range of height, main root length, total biomass of T. sinensis seedlings were all higer in the seedbed with shrub-grass and litter seedbed, or only shrub-grassunder 50% light conditions, indicating that it was beneficial for seedling growth to cover shrub-grass and litter moderately under moderate light intensity.2. Spreading mechanism of seed and its effect on seedling regenerationThe thousand seed weight of T. sinensis was very small compared to other plants, and the infructescence and seed weight and the seed plumpness all decrease with the increase of distance from mother trees. Each index of infructescence and seed at the middle position in forest gap was also lower. the results showed that the seed of T. sinensis mainly spreaded by wind..The infructescence weight and seed biological characteristics of T. sinensis all decreased with the increase of distance from the mother tree, and the seed vigor was the best at the distance of 2m or 4m from the mother tree, but that was lower at the distance of 6m or 8m from the mother tree. The results showed that the seed quality of T. sinensis decreased with the distance from the mother tree. Combined with the habitat information at the different distance from the mother tree, we found that the seed in T. sinensis can not spread to the suitable habitat for the seed germination and seedling growth and survival, indicating that the spreading restrictions existed during seedling regeneration, which maybe one of the main factors limiting the population regeneration of T. sinensis.