Studies On Water Consumption Characteristics Of Urban Greening Tree Species On Different Density

In this paper, the water consumption of main green tree species in Beijing city under different water supply and density was studied by using the method of simulated drought in greenhouse. Through analyzed the relationships between water consumption and soil moisture, leaf water potential of seedlings, the water consumption patterns of seedlings in normal water supply and drought stress conditions were observed. Target of the researches is to meet the need in choice of tree species with drought-tolerance and lower water consumption, higher survival rates in the semiarid areas of Beijing.The results of studies on water consumption of seedlings in normal water supply showed that the daily variations in quantities and rates of water consumption (WCQ and WCR) of seedlings were clearly. Moreover, the WCQs were half of that in whole day, and the highest hourly WCQs of the species were averagely 14.3% of that in whole day. The daytime WCQ of seedlings was occupied about 85% to 94% of the quantities of whole day. From the WCQs of the day time (8am~20pm) , the order from large to little was: Syringa oblata Lindl(217.4g),Pinus tabulaeformis Carr. (274.3g), Platycladus orientalist (352.4g), Buxus sinica Cheng ex M.Cheng. (376.2g), Fraxinus velutina Torr (453.1g) and Sophora japonica (517.0g) . With the increase of the density, the WCQs of the seedlings increased more and the WCQs decreased more. The extent of the WCQs of the seedlings increased was in the following order: Syringa oblata Lindl>Pinus tabulaeformis Carr>Platycladus orientalisl= Sophora japonica=Buxus sinica Cheng ex M.Cheng—Fraxinus velutina Torr. It was showed that with the increase of the density, the WCQ of Syringa oblata Lindl increased most and the extentof the WCQ of Platycladus orientalisl, Buxus sinica Cheng ex M.Cheng, Fraxinus velutina Torr and Sophora japonica increased just the same. The extent of the WCRs of the seedlings decreased was in the following order: Platycladus orientalisl > Pinus tabulaeformis Carr>Sophora japonica = Syringa oblata Lindl>Buxus sinica Cheng ex M.Cheng.—Fraxinus velutina Torr. The WCQ of trees is relevant to their WCR and leaf area, accordingly, it is very important to select tree species, which has lower water consumption and drought tolerance, and set reasonable stand density in recovery and reconstruction of tree vegetation. It is also showed that in the drought areas we should select Pinus tabulaeformis Carr, Platycladus orientalisL Syringa oblata Lindl and Buxus sinica Cheng ex M. Cheng which have little WCR , then choose Fraxinus velutina Torr and Sophora japonica.When the seedlings were subjected to drought stress, their daily variations of WCR and WCQ became unclearly. The WCQ and WCR of seedlings decreased when the seedlings were in drought stress, and, of which decreased sharply and were reduced over 50% in slight drought stress. The WCQ of most seedlings decreased by about 20% to 30%, some seedlings by about 10%, of that in norm al water supply condition when the seedlings were in medium drought stress. When the seedlings were subjected to serious drought stress, the WCQs of all tree species were few and were occupied less than 10% of that in normal water supply. The WCQ proportion between daytime and whole day was trend to decrease in drought stress.The water consumption of tree increased with increasing stand density, thus, the soil moisture decreased correspondingly. Therefore, the reasonable spatial structure and stand density in drought area would be beneficial to increase and maintain soil moisture and supply the base to the drought city of north China to choose the kind of green trees and ensure the reasonable density.