Tang An-Ching, Boyer John S
College of Marine Studies and College of Agriculture and Natural Resources, University of Delaware, Lewes, DE 19958, USA.
Funct Plant Biol. 2007 Feb;34(1):24-30. doi: 10.1071/FP06222.
Leaves often shrink significantly when soil water is limited. For gas exchange measurmements, the shrinkage can require correction for changing amounts of tissue in the apparatus. In sunflower plants (Helianthus annuus L.), a comparison was made between mathematically-corrected transpiration and clamping leaves at their original turgid size without mathematical correction. These methods should give the same result, but transpiration was substantially greater in the clamped leaves than in the shrunken and mathematically-corrected ones. Because the clamped leaves remained at their original turgid area, wounding was not a factor. If shrunken leaves were stretched to their original area, transpiration increased immediately and was traced to increased leaf conductance to water vapor and greater porosity for bulk air movement through the leaf, implicating the stomata. Releasing the leaf caused each of these properties to return to the tightened condition. When all the leaves were held at their original size during a soil water deficit, whole-plant water use was greater than when the leaves shrank naturally. It was concluded that shrinkage decreases the porosity of sunflower leaves. This natural tightening can be disrupted by stretching leaves during gas exchange measurements. However, stretching provides a useful means of changing leaf porosity for experimental purposes.
当土壤水分有限时，叶片常常会显著收缩。对于气体交换测量而言，这种收缩可能需要对仪器中组织数量的变化进行校正。在向日葵植株（Helianthus annuus L.）中，对经数学校正的蒸腾作用与将叶片夹在其原始膨胀大小而不进行数学校正的情况进行了比较。这些方法应该会得出相同的结果，但被夹住的叶片中的蒸腾作用明显大于收缩后经数学校正的叶片。由于被夹住的叶片保持在其原始膨胀面积，所以损伤不是一个因素。如果将收缩的叶片拉伸到其原始面积，蒸腾作用会立即增加，这可归因于叶片对水蒸气的导度增加以及大量空气通过叶片的孔隙率增大，这与气孔有关。松开叶片会使这些特性恢复到收紧状态。当在土壤水分亏缺期间所有叶片都保持在其原始大小时，整株植物的水分利用量大于叶片自然收缩时的情况。得出的结论是，收缩会降低向日葵叶片的孔隙率。在气体交换测量期间拉伸叶片会破坏这种自然收紧。然而，拉伸为出于实验目的改变叶片孔隙率提供了一种有用的方法。
