Study Of Physiological Characteristics Of The Alpine Treeline Trees In Mt. Gongga, Southwest China

There are many factors, just like low temperature, drought, alimentation short, salt stress, water stress, strong wind and so on, can restrict the distribution of forests, and make various forests limit. Alpine treeline ecotone is a very important environmental boundary to compartmentalize montane landscape types. Nowadays, the alpine life zone is one of the most fascinating regions for scientific research, due to 1) the steep environmental gradients within a short distance on a slope, 2) little human influence at high elevations, 3) the high sensitivity of alpine plants and their communities to a global change.Research on alpine treeline has a century-long history, five groups of hypothesis of treeline formation have been suggested on a local or regional scale: 1) the thermal limitation hypothesis; 2) the stress hypothesis; 3) the disturbance and growth limitation hypothesis; 4) the reproduction hypothesis; 5) the carbon balance hypothesis. However, a conclusive functional explanation of treeline formation on a global scale is still awaited. In China, mountainous region account for 70% in the whole country, and more than 95% in the southwest. But, the research about alpine treeline ecotone is not enough.This research studied the alpine treeline ecotone on the southeast of Tibetan Plateau. Select three tree species: Abies fabri, Picea likiangensis van hirtella and Tsuga dumosa, the major types of the alpine treeline trees, distributed form lower elevations until the alpine treeline in the warm and humid northeast slope(Mexi valley) and xerothermic southwest slope(Kangding valley), Mt. Gongga region, SW China. Investigated some physiological indexes, include LMA, NSC, N, soluble protein and so on, by using the theory and methods about plant bionomy, physiology and biochemistry. Study the altitudinal changes in physiological indexes of treeline trees at different entironment and different season. Answer whether treeline trees have lower carbohydrate concentrations compared to trees at lower elevations, and check the hypothesis "carbohydrate limit make the alpine treeline".The main results of the study are as follows:1. By researching the physiological indexes of treeline trees in the two slope of Mt. Gongga region, SW China, we can conclude that the warm and humid northeast slop(Mexi valley) is more suitable for treeline trees than the xerothermic southwest slope (Kangding valley). Therefore, the LMA, NSC, N, soluble protein and leaf NSC contents per area, leaf N contents per area, leaf protein contents per area of the trees in Mexi valley are obviously more than the trees in Kangding valley.2. By researching the physiological indexes of treeline trees in different season, the LMA, NSC, N, soluble protein and leaf NSC contents per area, leaf N contents per area, leaf protein contents per area of the tree at the end of dormancy are more than the same tree during the peak of shoot growth.This trend is more obvious in the tree in the warm and humid northeast slop(Mexi valley) than in the xerothermic southwest slope (Kangding valley). And in the same area, this trend is more obvious in Abies fabri than in other trees.3. Analysed the date of physiological indexes of treeline tree in different region, different season, different elevation, when the entironment or season or elevation changed, the physiological indexes of the trees, which have higher LMA, NSC, N, soluble protein and leaf NSC contents per area, leaf N contents per area, leaf protein contents per area, changed more significant than others. In another word, the changes of growth conditions observably affect the trees with higher carbohydrate values and grow in more suitable region than others.4. Compared the LMA, NSC, N, soluble protein and leaf NSC contents per area, leaf N contents per area, leaf protein contents per area of the three alpine treeline trees in two areas, the values of Abies fabri are obviously increased with elevation, especially during the peak of shoot growth; the values of Picea likiangensis var. hirtella are increased with elevation too. The contents of carbohydrate in the treeline tree are higher than in the lower elevation tree. There is no consistent evidence for carbon limitation in alpine treeline trees.5. This research obtained lots of data about physiological indexes in different treenline trees at the end of dormancy and during the peak of shoot growth. These data can be used for the study of alpine treeline ecotone in China or egional scale in the future.