Studies On Reproductive Characters Of Larix Chinensis

Larix chinensis is mainly distributed in Mt.Taibai, Shaanxi.lt is also scattered in other areas, such as Mt. Guangtou in Chang'an, Changqing National Nature Reserve in Yang County and Niubeiliang National Nature Reserve in Zhashui county. It is endangered in natural conditions. The main purpose of this thesis is to explore the reason why it was endangered from the angle of reproduction. Reproductive characters of Larix chinensis in were studied, including the spatial distribution of reproductive module, reproductive age, morphological and quantative characters of seeds and cones, reproductive value, the influences of plant size to fecuntity and seed size. The main results are following:1 The strobiles of Larix chinensis begin to differentiate in October, and develop next year. The female strobiles are located at the branch of 2-4 years old, and the male strobiles at the branches of 2-6 years old. The distribution is related not only to the age of a branch, but also to the place which growthed in the crown of a tree. The female strobiles are in the middle and uper layer of the crown. The male strobiles are much more in the middle and down layer. With the age increasing, the distribution of the strobiles has the trend of going up. Especilly inside the forest, almost all of the strobiles are in the upper layer.2 The average reproduction age is 78.59 years, the minimum reproduction age is 28 years, and the maximum reproduction age is 208 years. In south slope, the average reproduction age is 72.97years, the minimum reproduction age is 26 years, and the maximum reproduction age is 153 years. The average reproduction age is 92 years, the minimum reproduction age was 29 years, and the maximum reproduction age is 208 years in north slope. The average reproduction age shows positive correlation to altitude and annual precipitation, the maximum was positive correlation to slope, and negative correlation to minimum reproduction age, this demonstrates that the earlier reproduction decrease the time of reproduction.3 The fecuntity, seed size, cone size, NSC, TW, TWC show negative correlation toaltitude. The seed width, scale length, seed wing width, scale length, cone length, and the number of scale also are negative correlation to slope, The seed length to width and the seed wing length to width show negative to altitude, this means the variation of seed and seed wing is related to the diffuse of seeds. Temperature, slope and slope directionalso have influences on seed and cone morphlogy and quantative characters. SCLW is negative to slope; the cone width is positive to annual precipitation. The quantative characters of seeds and cones is negative correation to altitude, slope and slope direction, while positive to plant size. The seed number in cone showed positive correlation to mean temperature in January, and negative to mean temperature in July. The size of seed show positive correlation to the total number of seeds. There is no trade-off between the size of seed and the total number of seeds.4 Reproduction of Larix chinensis are influenced greatly by plant size. But the fecundity increases with the age while descent at 70 years old in south slope and 90 years in north slope. It also increases with altitude, but in north slope it was beginning to decent at about 3 300 m. The seed weight becomes heavier with the age increasing. But it becomes lighter in South Slope after 60 years old. With the altitude increasing, the seed weights become heavier at first, then lighter, but it become lighter at lower altitude in north slope.5 The reproductive value is correlated to age, but there are differences in different conditions. The reproductive value of north slope is higher than South slope, and the reproductive fitness is also higher in north slope. Before VII age class the RRVis higher in North slope, But the speed ofRRV descending with the age is faster in South slope.