油松人工林SPAC水势梯度时空变化规律及其对边材液流传输的影响

 利用热扩散式边材液流茎流探针（TDP）和微型自动气象站组成的测定系统于2001年4月在北京林业大学妙峰山教学实验林场（39°54′N，116°28′E）对低山油松（Pinus tabulaeformis）人工林土壤-植物-大气体（SPAC）界面水势梯度及油松木质部边材液流传输速率的时空变化规律及其相关因子进行了连续测定。土壤水势随深度下降逐渐升高，日周期波动幅度减小，灌水后上层土壤水势迅速提高，但随着水分扩散和林地持续蒸散，土壤湿度迅速下降并逐渐与对照趋同；叶片水势连日逐渐降低，灌水后水势较对照有一定程度提高；林冠不同层次叶片水势在日周期内不同时间差异显著，但同一层次之间差异不明显；油松人工林土壤、叶片、大气水势梯度比约为1∶5∶30，灌水后SPAC相临界面水势差增大，水势梯度提高至1∶15∶90。大气水分饱和亏缺与土壤水势和叶片水势、以及土壤水势与叶片水势之间均有极显著相关性。干旱春季灌溉对油松木质部边材液流时空波动产生很大影响，灌水后连日树干上位边材液流峰值出现时间推迟1 h，连日平均液流速率提高48.59%，连日平均最大液流速率提高25.12%。木质部边材液流速率日变化和连日变化与SPAC水势和气象因子如空气相对湿度、空气温度、太阳辐射强度密切相关。与对照相比，灌水后边材液流速率与SPAC各介质水势和界面水势差的相关性下降。

WATER POTENTIAL AND ITS IMPACT ON SAPWOOD FLOW VELOCITY

Spatial and temporal variations of the soil-plant-atmosphere-continuum (SPAC) water potential gradient and sapwood flow velocity in Pinus tabulaeformis and related factors were measured using a thermal dissipation probe (TDP) and micro-weather station that kept a continuous record of solar radiation, air temperature, air humidity, wind speed and wind direction, rainfall, and soil temperature at the teaching and researching station of Beijing Forestry University in West Mountains of Beijing in April 15-24, 2001. The results showed that soil humidity declined in the top layer soil and declined only to a small extent in the deep layer soil. Following a simulated rain event of 47.77 mm, surface soil water potential increased abruptly and water potential in the mid-layer soil increased after 2 days later but decreased and approached that of the control gradually due to wood evapotranspiration. Compared to the large water fluctuation in the surface and mid-layer soil, diurnal water potential in deep soil had stable daily fluctuations. The water potential of the SPAC elements decreased gradually from the soil to air. The soil-leaf-air water potential gradient of the rain treatment increased to 1∶15∶90 as compared to 1∶5∶30 of the control. Water potential differences of the leaf-soil, air-leaf and air-soil also increased after watering. The daily water potential of the SPAC elements declined gradually after a long drought period and declined in the following order: air>leaf>soil. The lowest daily leaf water potential occurred at 14∶00 pm, 4 hours earlier than the soil. The lowest air water potential occurred at the same time. Air temperature was the dominant environmental factor affecting air and soil water potential, and relative humidity of the atmosphere and soil moisture were the most important factors affecting leaf water potential. There were significant correlations between the surface soil and leaf water potentials the surface soil and air water potentials both for the treatment and control. Daily sapwood flow velocity (SFV) fluctuated in accordance with variations in the water potential of the SPAC elements and meteorological factors. Significant correlations were found between SFupper and 50 cm deep soil water potential, wind speed, solar radiation intensity, air humidity and air temperature, SFlower and soil temperature between 10-50 cm, wind speed, air humidity and air temperature for control, SFupper and wind speed, solar radiation intensity, air humidity and air temperature, SFlower and soil temperature between 10-50 cm for watering treatment. Correlation coefficients between SFV and the water potential of the different SPAC elements decreased with watering.