Study On Water Consumption Of Four Shrubs In The Desert And Arid Area In Northwest Of China

Transpiration, the crux for the bio-activity of plants, is essential for the physiological process of plants. Due to the special natural environment in the desert area in Northwest China, shrubs are the main species in afforestation in this region. So, it is of special significance to study the transpiration and water consumption of shrubs in this region.There are some factors affecting the transpiration of plants. The first one is the structure of physiological ecology such as conduit cavitation, sapwood embolism, branch restriction and capability of absorbing water; others are the environmental factors, such as intensity of illumination, relative air humidity, temperature and so on. In the research, plants' water consumption in 2004 was measured using Li-6200 portable photosynthetic analyzer and Stem-Flow gauges, and the water consumption of four shrubs in one growing season was estimated.Data analysis revealed that water consumptions of 4-year-old artificial H. ammodendron (Haloxylon ammodendron (Mey.) Bge.), T. ramosissima {Tamarix ramosissima Ledeb.), C. klememtzii(Calligonum klememtzii A. Los.) and H. scoparium (Hedysarum scoparium Fisch. et Mey), with the plantation density of 1200/hm~2, are 35.22mm, 62.53mm, 103.56mm and 32.96mm, respectively, in one growing season. Through trials, we found that C. klememtzii is suitable to be planted on the mobile sands at the early stage of desert control; H. ammodendron can be planted on the drift sand at the later stage of desert control; H. scoparium is suitable to be planted on the low terrain among sand dunes; and T. ramosissima can be planted in the shelter belt to protect oasis.In one growing season, the curves of transpiration rate take shapes of single-peaks, while the stomata conductance varies at the same time within a day. The order of average value of the stomata conductance, from low to high, is T. ramosissima, C. klememtzii, H.ammodendron and H.scoparium. The order of transpiration rate, from low to high, is C. klememtzii, T. ramosissima, H.ammodendwn, H.scoparium. The order of water use efficiency, from low to high, is H.scoparium, T. ramosissima, C. klememtzii, H.ammodendron.It is found that there are different environmental factors that play a leading role in different periods. For example, meteorological factors are of importance in influencing the changing of daily transpiration rate, especially, temperature is more closely related to daily transpiration rate. Vapor pressure is significant for daily transpiration rate of T. ramosissima and H. ammodendron. However, water content in the soil affects the transpiration rate in a long run.The study showed that the regularities of daily sap flow rate are different from each other in one growth period while they are similar within a short period of one week. Its changing curve is like a "narrow peak" for trunk while like a "wide peak" for important and secondary grade branches.The overwhelming majority of sap flow appears in the daytime, and it drops to zero between 5:30—7:00. The starting and stopping time of sap flow of the important branch is the same with that of trunk. The sap flow of the secondary branch is keeping in existence in 24 hours. The ratio, flowing capacity of night to daytime, of the secondary branch is higher than that of the trunk and important branch, there is even a phenomenon "it is lower in daytime while higher in night".The orders of sap flow rate and capacity, from the highest to the lowest, are the trunk>the important branch > the secondary branch. The sap flow flux is more complex, in ordinary circumstances, it is lower for the trunk. Among the leading meteorological factors that influence the changing of sap flow rate, the intensity of illumination is the key one, temperature is the second one, and then the relative humidity.