Populus Euphratica Reproduction Characteristics Of A Degradation Oasis Vegetation In The Extreme Arid Regions

Populus euphratica, distributed along the sides of inland rivers, is the only one species that can formulate the forest community in the north-west arid regions of China. The riparian ecosystems are facing the dangers of degrading or even collapsing due to the unreasoned water utilization by human being. It is an immediate demand to protect the endangering Populus euphratica population. The proposed investigation is carried on seedling bank, seed rain, the effects of different environmental factors on the seed germination of Populus euphratica in Ejina oasis, Inner Mongolia.There is very little number of seedlings in the forest, Populus euphratica depends on asexual reproduction to sustain. The maternal trees can produce a large number of seeds with vigor. The seed rain duration of a plot fell into three successive phases-starting phase, fastigium phase and subsidizing phase. Humidity and wind had great effects on the seed dispersal. The seed rain intensity was positively correlated to humidity, most seed dispersed in the noon and afternoon when the humidity was relatively low in daylight. The longevity of the seeds under full light and shade conditions were 6d and 40d,respectively. We found that wind affected direction and distance of seed dispersal: the majority of the seeds distributed close to the maternal trees, only a little part of seeds had long-distance dispersal. Wind factor determined direction and distance of the seed dispersal. In the direction of wind, seeds had dispersal with longest distance, almost all the long-distance dispersal took place in this direction; in the vertical and upwind direction, the seeds were more likely to distribute close to the maternal tress. The wind speed was highest between noon andearly afternoon, and the seed rain intensity got the climax simultaneously. The synchronization of wind speed and seed rain intensity was an effective plant-controlled mechanism that facilitates Populus euphratica's seed long-distance dispersal. Duo to the brevity of seed longevity under natural conditions, the difference of seed rain time among the three plots in our study might result from Populus euphratica's adaptation to the temporal changes of the flood.The result of seed germination shows that the germination percent of fresh seeds is 100, drought stress and salt stress have significant negative effect on the seed germination, light and temperature's influence on seed germination is not significant.One of the innovative contents in the study is that for the first time, two plant-controlled mechanism in Populus euphratica's reproduction is presented: the risk-spreading mechanism and r-K continuum mechanism. Another innovative contents in the study is that we investigated Populus euphratica's seed rain quantitatively and by utilizing the weather station we found the relationship between the seed rain intensity with the humidity.