A Study On Transpiration Characteristics Of Chinese Fir Plantation

This paper applies ICT-2000TE (Transpiration-Environment) stem sap flow and automatically microclimate measure system, which was based on the Thermal-Dissipation principle, to study the following contents in Hui Tong second generation Chinese fir plantation's growing seasons of 2006:the daily and seasonal variations of stem sap flow density of the sample tree, the relationships between stem sap flow density and environmental factors. Then establishes the following models: multiple regression model of daily variations of stem sap flow density and environmental factors under different weather conditions and different periods in growing seasons, sap flow density model in clear and cloudy day of sample tree, daily water consumption model of sample tree. After these works, this paper estimates the water consumption of transpiration of sample tree and Chinese fir plantation.The research indicated that, the daily variations of stem sap flow density of the sample tree is an unimodal curve in clear day and the unimodal, bimodal or the multi-peak curve combination in cloudy and rainy day. The phenomenon of days and nights alternate is obvious. In the growing seasons, there still has a weak stem sap flow rising at night and the main driving force is root pressure. The stem sap flow densities have much more different between kinds of growing seasons. Comparing the daily sap flow density and mean value of the peak value, we find that summer> spring> autumn, clear day> cloudy day> rainy day.Using multiple regression analysis to find out the environmental factors which influence the stem sap flow in different growing period, and the results are as follows: clear day is the average air temperature, average soil temperature (negative effect), the average air saturation deficit, cloudy day is the humidity of the air (negative effect), PAR, the average air saturation deficit, the average air temperature and soil temperatures (negative effect); rainy day is the average soil temperature(negative effect), PAR, the average soil temperature(negative effect), the average air temperature and relative humidity of the air (negative effect).The variations of stem sap flow density of the sample tree assume the bimodal curve in the growing seasons (March to November).The first peak value 10.724 cm3cm-2h-1 appears in June summer growing season, after that appears a lower value 5.139cm3cm-2h-1 in July, then august presents second peak value 6.877 cm3cm-2 h-1. The value in September (2.511 cm3cm-2h-1) falls to the value that closes to the value in March (3.081 cm3cm-2h-1). In each periods of growing seasons,the correlation analysis in photosynthesis effective radiation, the average air temperature, the average soil temperature, the average soil moisture and so on indicate that only the average air temperature has higher correlation and reach the extremely remarkable level, other factors assume small correlation.The sample tree consumes 2604.33kg water in the whole growing seasons and mainly distributes in May to August. The water consumption in May to August occupies 68.9% of the entire growing seasons'water consumption. The spring, summer and autumn growing periods'water consumption respectively occupies the proportion of entire growing season's water consumption is:27.8%,58.1% and 14.1%.Using east, west, south and north directions'sapwood thicknesses of 32 Chinese firs, whose DBH and growing trend are commensurate to sample tree, and the 32 Chinese firs are growing by the side of sample tree. We established regression equation(S= 21.877e01028D) between the sapwood area and the DBH, then Combining with the DBH of the sample tree and the quadratic-trend-surface models of sap flow density, we build the daily water consumption model in clear day and the cloudy day:Because of the complexity of environment factor's function, the size of sample and the applicability of model and so on, the model's simulation effects are not very ideal, and needs more accurate model.Throughout the growing season (March-November), the Chinese fir plantation stand in the sample field (area is 0.066667ha) have total transpiration of 788.52 mm. If annual average rainfall is 1100-1400mm, in the growing seasons, Chinese fir plantation's transpiration accounted for 56%-72% of the rainfall.Monthly variation of transpiration is the bimodal curve, it increases gradually from March, and reaches a peak value 212.28 mm in June. After that because of the higher temperature or intermittent growth and other factors in July, the transpiration drops to only 105.13 mm. The transpiration increased to 140.67 mm in august and appears the second peak value. In autumn growing season, Chinese fir plantation stand's transpiration gradually drops to the value that is before the spring growing season's value.