叶片滞留水对森林蒸腾过程的影响机制研究

Forest transpiration, as the primary consumption of forest soil moisture, is an important component of terrestrial ecosystems evapotranspiration. To correctly and comprehensively understand the impact factors of transpiration and the underlying mechanisms is very important to accurately assess and predict the land water cycle processes. Leaf retained water (LRW), appears frequently during\after rainfall and fog, or occurs as dew in the humid area or season, is an important impact factor of transpiration and should be paid sufficient attention. However, most forest transpiration models were built under the condition of dry leaf surfaces or canopy, so the forest transpiration cannot be separated from canopy evapotranspiration. Therefore, the influence of LRW on transpiration of humid temperate forest, broadleaf Korean pine forest will be studied in this research. The six dominant species of the forest will be chosen as research materials, to probe the relationship between tree transpiration rate and the amount of LRW, by using classical weighing and sap flow method to detect the transpirations of the trees sprayed with water and the tree of check samples. The physical and physiological impacting mechanism of LRW on tree transpiration will be studied by synchronous measurements on leaf and canopy temperatures and reflections. And the mechanism will be coupled into the forest transpiration model, and the LRW influenced transpiration model will be obtained. We expect the revised model to improve the predicting precision of broadleaf Korean pine forest transpiration with LRW under different rainfall frequency and rainfall amount, which will be useful for forest water cycle researches under global change.

森林蒸腾是陆地生态系统蒸散的重要组分,对于雨、露和雾频发的森林地区，液态水覆盖叶面时间相对较长，叶片滞留水作为一个常见的蒸腾影响因素应该受到足够重视，但现有蒸腾模型均针对无滞留水的干燥叶面或冠层，无法计算和区分森林蒸散量中的蒸腾量值。针对上述存在问题，本项目针对雨露频发的长白山阔叶红松林，选择6个主要树种为研究对象，拟采用人工喷水方法模拟幼树和成树树冠滞留水，利用经典的称重和树干液流方法测定树木蒸腾量，探索我国温带主要树种蒸腾量与树冠滞留水量的关系，结合滞留水影响下叶片和树冠表面反射、温度等参数的同步测定，揭示树冠滞留水对树木蒸腾影响的物理和生理机制，并将相应的方程耦合入林冠蒸腾的机理模型，构建滞留水影响下树木蒸腾模型并进行检验，提高森林蒸腾模型在湿润冠层下的模拟精度，评估、预测不同降水频率和降量影响下长白山阔叶红松林蒸腾耗水量的变化，为全球变化背景下森林水循环研究提供基础.

森林蒸腾是陆地生态系统蒸散的重要组分,对于雨、露和雾频发的森林地区，液态水覆盖叶面时间相对较长，叶片滞留水作为一个常见的蒸腾影响因素应该受到足够重视。本项目针对雨露频发的长白山阔叶红松林，选择6个主要树种为研究对象，采用人工喷水方法模拟幼树和成树树冠滞留水，利用经典的称重和树干液流方法测定树木蒸腾量，探索我国温带主要树种蒸腾量与树冠滞留水量的关系，结果显示：叶片表面水滴形态是阐述滞留水分影响蒸腾理论的微观基础。在等水量情况下，蒙古栎、色木槭、紫椴、水曲柳叶片上水滴覆盖面积依次增大，水滴形态呈现相对扁平的趋势。叶片表面滞留水存在及其蒸发对气孔开度的影响较大，在滞留水蒸发的过程中，气孔普遍开度降低10-60%，加上当植被叶面存在滞留水分时，由于液态水堵塞部分气孔，植被蒸腾量减少，而且液态水的蒸发阻力远小于蒸腾发生过程中的阻力，滞留水分的蒸发挤占蒸腾过程应分得的潜在蒸散力份额，从而影响蒸腾过程。研究确定了叶片滞留水分对树木蒸腾的影响为抑制作用。抑制率在一定的范围内随滞留水量的增加而增大。滞留水对阔叶树种蒸腾的抑制能力大于针叶树种，由于叶表水滴的蒸发由于水滴表面积不同呈非匀速变化过程。相对亲水叶片上，等水量水滴蒸发速率快，影响时间短；反之，在亲水性相对差的叶表水滴，蒸发速率慢，但影响时间长。故对于叶片亲水性好的树种抑制率高。抑制率在一定的范围内随滞留水量的增大而增加；当水量到一定值时，则抑制率不再增加。降雨后在相对亲水叶表更易形成膜状水，覆盖气孔能力较强，而在相对斥水叶表，水分更易汇集，覆盖面积相对少，抑制蒸腾能力较弱。叶片滞留水分对测试植株的平均抑制率分别为27%-58%不等。本研究揭示树冠滞留水对树木蒸腾影响的物理和生理机制，提高森林蒸腾模型在湿润冠层下的模拟精度，为评估、预测不同降水频率和降量影响下长白山阔叶红松林蒸腾耗水量的变化，及全球变化背景下森林水循环研究提供基础。