Study On Water Consumption Of Three Ornamental Tree Species In Common Use In Beijing

Focusing on the hot topics on the shortage of water resources which affects the sustainable development of Beijing city, this article takes three ornamental tree species including Magnolia denudata Desr., Liriodendron Chinense Sarg. and Robinia pseudoacacia L. which are in commom use in Beijing as its objects, applies the thermal dissipation sap flow probe (TDP) and the attomatic micro weather station(WS-UM)to long-term state observations on sap flow of trunks and environmental factors of trees. Based on these research results, the author concludes the fluctuation law of water consumption of three tree species, makes a water consumption comparison among the different trees, builds up a relationship model between water consumption and dominant environmental factors and makes a scaling up. All of these conclusions will provide theoretical basis for establishing the irrigation schedule and enhancing water use efficiency of green spaces in city.Results showed that the daily course of sapflow velocity of three tree species showed as peaked curves. The diurnal fluctuation of Magnolia denudata Desr. showed as a single-peaked curve. Every day ,the starting time and the peak-appearing time are the latest, the peak height and average sap flow velocity are the biggest, and the lowlands-appearing time is the earliest. Generally, the diurnal SFV of Magnolia denudata Desr. starts about from 8:10 to 8:40, and ascends to the peak about from 14:10 to 14:30, the peak is about 0.00852 centimeter per second and the average sap flow velocity is about 0.00173 centimeter per second, then about from 18:10 to 19:00 ,the lowlands appears.The diurnal fluctuation of Liriodendron Chinense Sarg. and Robinia pseudoacacia L. showed as wide-peaked curves. Every day ,the starting time and the peak-appearing time of Robinia pseudoacacia L. are the earliest, the peak height and average sap flow velocity are the smallest, and the lowlands-appearing time is the latest. Generally, the diurnal SFV of Robinia pseudoacacia L.starts about from 6:30 to 6:40, and ascends to the peak about from 9:10 to 11:20, the peak is about 0.00170 centimeter per second and the average sap flow velocity is about 0.00063 centimeter per second, then about from 19:30 to 20:20 ,the lowlands appears.The diurnal fluctuation of Liriodendron Chinense Sarg. is between the other two tree species. Generally, the diurnal SFV of Robinia pseudoacacia L.starts about from 7:30 to 7:50, and ascends to the peak about from 11:00 to 12:40, the peak is about 0.00236 centimeter per second and the average sap flow velocity is about 0.00092 centimeter per second, then about from 19:30 to 19:50 ,the lowlands appears.The time the sapflow velocity of the peak of three free species sustained in summer is longer than in spring and in winter, but the peak height and the average sapflow velocity in summer are lower than in spring and in winter.The Comparison of the water consumption ability among three free species is made. The average sap flux of Magnolia denudata Desr., Liriodendmn Chinense Sarg. and Robinia pseudoacacia L. are 5.740 cm³Â·h^-1cm^-2, 4.695 cm³Â·h^-1·cm^-2 and 2.947cm³Â·h^-1 ·cm^-2, therefore, the ability of water consumption of three free species is as following: Magnolia denudata Desr. > Liriodendron Chinense Sarg. > Robinia pseudoacacia L.. The average sap flux of three free species in spring and in autumn is bigger than in summer. It mostly attributes to the effect of the growth rhythm of trees and environmental factors. In three typical weather, the fluctuation law during the whole growing season of three free species is as following: sunny > cloudy > rainy, and the percentage of sap flux in daytime account for sap flux at night is as following: rainy > cloudy > sunny.It also showed that there was almost no relationship between the stem sapflow velocity and the stem diameter of Robinia pseudoacacia L., but the daily water consumption of single free is notably related to the trunk diameter and sapwood area .The correlation coefficient were 0.983 and 0.999. In addition, because of the effect on the water capacitance of free, the peak shape of the SFV curve in smaller diameter was more narrow than in bigger diameter.Correlation between dominant environmental factors and stem sap flow speed of trunks is summed up. Results indicate that the main factors of affecting the stem sap flow speed of trunks of three free species are air temperature, air relative humidity and sun radiation. Furthermore, sixty linear regression models are created based on dominant environmental factors and stem sap flow speed of trunks. In these models, the simulating effect in cloudy and rainy is worse than in sunny. But the error of the daily water consumption between predicted result by model and experimental result has no large difference, and the average error rate is less than ±10%. Therefore, the linear regression models built have application value.Based on the study on the fluctuation law of water consumption and the linear regression models of water consumption, the water consumption of Robinia pseudoacacia L.is calculated by scaling up the correlation model between diameter and water consumption, namely, by scaling up the correlation model W=0.118D^1.533. It can predicted the water consumption of Robinia pseudoacacia L in arbitrary diameter in different weather of each month and made us easy to master the fluctuation law of water consumption.