白桦树干液流的动态研究

A Researches on Stem Sap Flow Dynamics of Betula platyphylla

应用热扩散原理 ,采用 ICT-2 0 0 0 TE(Transpiration-Environment)自动监测系统 ,对东北东部山区的先锋树种白桦的树干液流及主要环境因子进行一个生长季的同步测定。结果表明 ,在整个生长季的晴天 ,白桦树干液流的日变化呈现明显的单峰曲线。液流速率的峰值出现在 8月中旬 ,为 84.72 L/ d。在白桦树叶脱落后 ,仍有较高的液流速率 ,而到 1 0月中旬急剧下降 ,值为 3 .84L/ d。在不同生长时期白桦每小时的液流速率与相应的环境因子逐步回归分析结果表明 ,影响白桦液流速率的主要环境因子是空气温度、空气相对湿度和辐射强度 ,在不同时期三者的作用是不同的。

A study of whole tree sap flow of Betula platyphylla was conducted during the 2000 growing season. The study area was located at the Forest Ecosystem Research Station (127°30′～127°34′E Longitude, 45°20′～45°25′N Latitude) in the Maoershan Experimental Forest, Northeast Forestry University, Heilongjiang Province. Within the Maoershan range, the average elevation is 300m and the highest peak is 805m. The undulating slope of the terrain generally ranges from 10° to 15°. The zonal soil is dark brown forest soil. The climatic conditions of the area are typically continental cold temperate. The mean annual temperature is 2.8℃. The annual cumulative temperature of ≥5℃ is 2897℃. The annual total sunshine amounts to 1850.4h. The mean annual precipitation is 772 9mm, with more than 60% concentrated in two months of the summer. The mean annual evaporation is 884.4mm and wind speed averages 1 5m/s.The frost free period ranges from the end of May to the end of August. In the present paper, the thermal dissipation method proposed by Granier was used to measure sap flow rate of Betula platyphylla . The thermal dissipation probe (TDP, Dynamax, Houston TX, USA) consisted of two cylindrical probes of 1.32mm in diameter. The probes were inserted horizontally 3 cm into the sapwood of the tree trunk with one probe 40cm above the other. The upper probe contained a constantan heating element, which was heated at constant power. Each probe contained a copper constantan thermocouple, connected in opposition for measuring the temperature difference. Sap flow rate was calculated using the following equation: Fs =0 0119× SA×K 1 231 , where Fs was the sap flow rate (L/h); SA was the sapwood area at the level of the heated probe (cm 2); and K , the dimensionless flow index ( K= [dTM dT] / d T , where d TM was the temperature difference between probes without any sap flow and d T was the temperature difference with sap flow). The precision of estimation of transpiration depends on the accuracy of the differential temperature measurement. The thermocouples must be protected against direct radiation and rain. The environmental sensors installed above the tree crown included an RH 1 humidity and temperature probe (Vaisala, UT,U.S.A), an SKP215 PAR Quantum Sensor (Skye, U.K.), an SKS1110 Silicon Cell Pyranometer (Skye, U.K.), an A100R wind sensor (Vector Instruments, U.K.), and a GMP111 CO 2 transmitter (Vaisala, UT,U.S.A). An STC soil temperature sensor (Delta T Devices Ltd., Cambridge, U.K.) and an MP406 moisture probe (ICT Ltd. Australia) were used to monitor the root zone soil temperature and soil volumetric water content. Rainfall was measured in an open space nearby with an ARG100 tipping bucket rain gauge (EM LTD., U.S.A.). The TDP and all environmental sensors were sampled every 15min (ZENO3200, Coastal Environmental systems, U.S.A.). Sap flow rate exhibited mono peak patterns during clear sky days. During the growing season, the maximum sap flow rate 84 72 L/d, occurred at mid August. The sap flow persisted after leaf senescence until the mid October. Results of statistical analysis indicated that air temperature, relative humidity, and solar radiation were the major factors affecting sap flow rate on clear sky days in different growth periods.