Water Ecological Characteristics Of Platycladus Orientalis In Semi-arid Region On Loess Plateau

Semi-arid region on Loess Plateau is a typical area in our country. In this area, soil water condition is deficiency in a long time. So water is one of the most important factors in the forestation. Platycladus orientalis is one kind of the main trees spices on Loess Plateau. But the relation between the growth of Platycladus orientalis and the soil water content is not clearly. This dissertation utilized advanced apparatus, equipments and various approaches, systematically analyzed of relationship between wood production with water consumption and studied the ecophysiological characteristics of tree transpiration and water consumption.In the research, we chose 2 years old Platycladus orientalis to be the experiment material, control the soil water content at 5 grads (5%, 10%, 15%, 20%, 25%) with TDR. Observe the transpiration rate and the net photosynthetic rate from May to October in 2005, the results indicate as following:1. In different season and different soil water content, the daily change in transpiration rate and net photosynthetic rate of Platycladus orientalis has three types. When the soil water content at a high level, the Tr and Pn demonstrated single-peak curve in daily change. In treatment middle water stress, the curve is double-peak, and in the serious water stress, it was demonstrated several-peak curve.2. Under different soil water content, the season change of Tr and Pn have the same disciplinarian. When the soil water content is above 10%, the season change of Tr and Pn are single-peak curve, and the peak appear in July. But when it is at 5% grad, the season change is not very clearly, the curve did not have an obvious peak.3. The Tr and Pn was change as the SWC change. When the SWC is below 18.15%, Tr is increase obviously, but not obviously when SWC is above 18.15%. From May to October, the suitable soil water condition for Pn is 24.12%, 24.41%, 28.40%,20.25%, and 18.79%. According to the results, it is clearly that the SWC for Platycladus orientalis growth is higher in spring than in autumn.4. According to the results, the sun radiation is the most important factor in weather conditions, and then is the air temperature and relative humidity. But in different SWC, the relationship between weather factors and Tr, Pn is different. The relationship is lower when the SWC is lower, and the SWC is high, the relationship is also high.5. In this research a regression equation between Tr and Rs was established asTr = 24.606Rs^-1.038, and the Pn, Gs was Pn = -566.4Gs² +185.37Gs - 2.8566. As the SWCis increase the relationship between stoma and Tr Pn is significance.6. The daily change of WUE is different in different season and different SWC. The curve like U, W and abnormity three types has three types. According to the results, it is known that Pn has the more relation to WUE. The range of the suitable SWC is 10%-15%. In this range, the WUE is at a high level, and out the range the WUE is lower than at the range. When the SWC is 13.16%, the WUE is the highest The results indicated that moderation drought is good for WUE of Platycladus orientalis.7. SWC is important for water consumption distribution in different seasons. The water consumption of Platycladus orientalis is lowest in October, and from June to August, the water consumption is at a high level. According to the results, the suitable SWC is about 25% for growth of Platycladus orientalis.