Study On Rules Of Water Consumption Based On Sap Flow Of Main Tree Species In Eco-conservation Belt Of Beijing

Seedlings and individual plants of common trees species and common stands in Eco-conservation Belt of Beijing were selected as the research objects in this article. A compared research that rules of water consumption of seedlings of seven tree species (Pinus tabulaeformis, Robinia pseudoacacia, Quercus. dentata, Acer truncatum, Rhus chinensis, Vitex negundo Var.heterophylla, cotinus coggygria) in pot experiment measured with micro-lysimeter and thermal dissipation technology was done and the rules of sap flow of individual plants five tree species(Pinus tabulaeformis, Platycladus orientalis, Q. variabilis, Robinia pseudoacacia, Acer truncatum) were studied to reveal the characters of transportation. The relationship between the sap flow of individual plants and per micro-meteorological factor was studied, and the fitting models between which were established. In addition, a prediction model for water consumption of individual plant based on grey relational analysis and RBF artificial neural network was founded to simulate the rules of sap flow accurately. Subsequently, the stand scale extended model based on sap flow was set up according to the relationship between sapwood area and DBH. The results above could provide exactly basic data and scientific theory support for the forest construction, management and reconstruction in Eco-conservation Belt of Beijing. The results showed that:(1) The character of micro-lysimeter method is simple to operate and convenient for application, on the contrary, the packaged stem sap flow gauge method has higher precision and complex operation relatively, and the instrument is more expensive. Both the micro-lysimeter method and the packaged stem sap flow gauge method can reveal the rules of transportation of seedlings, however, there is no significant differences between the two results according to the paired sample T test on the water consumption measured by two methods. The two experiment results were comprehensive comparative analyzed, which showed that the transportation ordination of broadleaf arbor seedlings was:Rhus chinensi> Acer truncatum> Robinia pseudoacacia> Quercus. dentata; the transportation ordination of shrub seedlings was:Vitex negundo Var.heterophylla> cotinus coggygria; the transportation ordination of coniferous arbor seedlings measured micro-lysimeter with was: Pinus tabulaeformis> Platycladus orientalis.(2) According to the characters of diurnal water consumption measured by the packaged stem sap flow gauge, it is revealed that the proportion of night water consumption of shrub seedlings is the biggest, the proportion of coniferous arbor seedlings is lower than that of shrub seedlings, and the proportion of broadleaf arbor seedlings is the lowest.(3) During the research on the sap flow of individual plant, it is founded that both the diurnal change curves of the sap flow velocity of Pinus tabulaeformis and Platycladus orientalis were single peak type, and the sap flow velocity of Platycladus orientalis is higher than that of Pinus tabulaeformis in typical sunny day during the five months; the diurnal mean sap flow velocity ordination in typical sunny day is:Robinia pseudoacacia> Quercus. dentata> Q. variabilis. Compared with the transportation water consumption of five tree species, not only the sap flow velocity and the transportation time had influence on the water consumption, but also the sapwood area did. Although the sap flow velocity of Pinus tabulaeformis is lower than Platycladus orientalis, but the sapwood area of Pinus tabulaeformis is larger, so the total water consumption of Pinus tabulaeformis is higher than that of Platycladus orientalis.(4) In typical sunny days, the physiological structure and ecological characteristics of the individual plant leaded to the different relationship between the individual plant and each micro-meteorological factor. However, after fitting the sap flow velocity to air temperature, Air Relative Humidity, solar radiation, soil temperature, it is showed that the correlation coefficient of the fitting equation is more than 0.9, but the correlation coefficient of the fitting equation between the sap flow velocity and the average wind speed was not significant.(5) The water consumption prediction model of individual plant based on grey relational analysis and RBF artificial neural network was established by the measured data in typical sunny days in Aug.2008. According to the test by measured data, the biggest absolute error of this prediction model is 0.0577 cm/h, the minimum absolute error is 0. 0009 cm/h, and the average value is 0.0111 cm/h. And the biggest relative error of this prediction model is 1.6613%, the minimum absolute error is 0.0557%, and the average value is 0.6134%. Obviously the model has better prediction effect.(6) The fitting equations, the correlation coefficient of which is good, between sapwood area and DBH of five tree species (Pinus tabulaeformis, Platycladus orientalis, Q. variabilis, Robinia pseudoacacia, Acer truncatum) were established. Taking Pinus tabulaeformis for example, the sap flow velocity increases with DBH changing bigger, and the diurnal variation trend of the sap flow velocity of Pinus tabulaeformis was basically identical. In addition, the prediction model for daily cumulative water consumption of Pinus tabulaeformis with different DBH was established based on Richards growth model. Subsequently, this model was extended to predict the water consumption of the stand scale, according to the number of different diameter class trees. The results of the research on stand scale water consumption in the experimental field showed that:the water consumption of Pinus tabulaeformis stand is 17769.8 kg/hm2in typical sunny days.