A Study On Physiological And Ecological Characters Of Qilian Juniper

Qilian Juniper is the longest living endemic tree species in the northeaster Tibetan Plateau, due to the hash environment of its growth and the impact of environment stress, Qilian juniper grows extremely slowly under natural conditions. So it has been widely employed in tree ring based climate research in the arid and semi arid areas, which plays an import role to understand the past climate change and predict future climate development trends. Many studies have shown that there is instable relationship between the Qilian junpier and climate factors, but the mechanism is not available. Therefore, understanding the relationship between the physiological and ecological characters of Qilian juniper and its impact facts can provide a theoretical basis to tree ring response to climate change, and also provide a scientific basis fot the local species protection.Photosynthesis can manufacture the organic matter what is the main energy for the plant growth, so the strength of photosynthesis determines the plants’growth to some extent. Sap flow as an important indicator in plant transpiration, has been widely used in the prediction and evaluation for the water use efficiency and water consumption in forest. Based on the biological basis and tree rings ecological methods, in this article, we selected4Qilian Juniper to do long-term physiological and ecological observation in timberline of the National Forest Park,the observation index including photosynthesis, transpiration. and sap flow and meteorological factors. Through the analysis of the relationship in photosynthesis, diurnal or seasonal variation of sap flow and the environmental factors, to reveal the mechanisms of climate response in the Qilian Juniper.During2010to2012, dirunal and seasonal variations of photosynthesis of Qilian juniper and variations change between different months in growing season were studide by Li-6400porlarble photosynthetic system under natural condition. The result showed:(1) there are two trends in Qilian juniper diurnal change,"single peak" and "double peak" respectively. The April showed "single peak", at which the Pn reaches the peak value at10:00. The curve of durnal variation in net photosynthesis rate (Pn) in other month has a double peak, at which the Pn reaches the peak value at10:00and16:00and reach the minimum value at14:00. And this indicate that there existed "minday depression" in the photosynthesis of Qilian juniper.(2) There has an obvious seasonal variations in Qilian juniper photosynthesis. Throughout the growing season, photosynthesis in May was signicantly higher than in other months, Pn between the different months showed the flowing variation:May> July> August> June> April.(3) The regression analysis found that there are different factors affect the Qilian juniper in different month, but the temperature is the common factor affecting the Qilian juniper. Correlation analysis and path analysis results show that there are significant negative correlation between the Qilian juniper photosynthesis and mean air temperature. It is popular that the significant positive correlation between the transpiration rate and stomatal conductance. The direct path follow:Gs>Tr>PAR>RH>Ci>Ta, the decision coefficient display:Gs>Tr>Ta>RH>Ci>PAR. Above all, the stomatal conductance is a main physiological factors that affects the Qilian Juniper photosynthesis, and the temperature is a key climate factor affecing photosynthesis.There has an obvious dirunal and seasonal variations in sap flow.(1) The results show that the stem sap flow behaves as a single-peak curve in sunny day, but there have different trends in different weather conditions, on clody or rainy days, the stem sap now showed "double peak" or "multi-peak" trends.(2) There are diffetent dirunal changes in different season, such as the sap flow starting time, stop time and the time that the sap flow reach the peak. Throughout the growing season, the sap How between the different months showed the flowing variation:August> July> June> May> October> December> September.(3) There exist a significant lag between the sap flow and solar radiation, our result showed that different lag between sap flow and solar radiation in different months.(4) A number of factors affect the Qilian juniper sap flow, specifically, the sap flow was rising with temperature by exponentially, the equation is Y=72.852e0.0986x; The sap flow was rising with solar radition by power function, the equation is Y=5.1458x0.6421, and it was decreasing with relative humidity by negative exponential, the equation is Y=922.26e-0.0214x.There is a complicated relationship between soil water content and sap flow. When the soil water content is less than0.13, the sap flow was rising rapidly, the eqution is Y=14.359e21.989x, when soil water content greater than0.13, the relationship between sap flow and soil water content is Y=1611.1x-20.33.(5) Stepwise regression analysis found that the factors affecting sap flow were air temperature> soil temperature> relative humidity> photosynthetically active radiation, this indicate that temperature is a determining factor in Qilian juniper transpiration.On the basis of these observations, we also conducted a cambium paraffin section analysis, the result show that the cambium start to divide in April and May is the cambium rapidly dividing period. During this time, the formation of rings accounted for65.5%of all biomass. July and August accounted for9.30%and7.52%respectively. In addition, we collected46cores from23trees in observation point, after pre-processing and cross-dating, develop a tree-ring with chronology and make the correlation with meteorolofical factors. The result showed that there was a significant negatively correlation between tree-ring width and the temperature of January and May. Many reasons can explain this response pattern, firstly, the photosynthesis is strongest in May and this is a critical period of nutrient accumulation, but in other month, high temperature limited the process of photosynthesis. While cambium is the most active in July, and this period is very important for ring with. Therefore, the accumulaion of nutrients in May provides sufficient energy for growth of the Qilian juniper at this time. So we can say that the intensity of photosynthesis in May detirmine the tree-ring width.