ADAPTATIONS AND RESPONSES TO DROUGHT IN QUERCUS SPECIES OF NORTH-AMERICA
ADAPTATIONS AND RESPONSES TO DROUGHT IN QUERCUS SPECIES OF NORTH-AMERICA
复制标题
DOI：
10.1093/treephys/7.1-2-3-4.227
复制
发表时间：
1990-12-01
期刊：
影响因子：
4
通讯作者：
ABRAMS, MD
中科院分区：
文献类型：
--
作者：
ABRAMS, MD
大多数北美栎树(Quercus spp.)通过避免或容忍水分胁迫，或两者兼而有之的能力，适应干旱易发地点。一般来说，它们有深入的根系，使它们能够在干旱期间保持相对较高的黎明前水势。橡树叶厚，一些气孔相对较小，这两个特征都有利于高水分利用效率。然而，一些来自温暖地区的物种有很大的气孔孔。大气孔使快速蒸发冷却成为可能，这可能是对高温的适应。东南部的一些树种在干旱时表现出卷叶，而加州土生土长的Q.doutarsii是干旱落叶的。橡树的木质部具有环状多孔结构，当土壤水分充足时，可以在大直径的早期木材导管中快速移动汁液，而在干旱期间，可以在较窄的晚期木材导管中进行缓慢但持续的水分移动，这些导管更耐汽蚀。在较低的叶水势和较高的水汽压差下，橡树经常比其他属的共生物种保持较高的光合作用速率。一个例外是红栎属，它通常局限于相对中等的地点。在干旱期间，许多橡树品种，特别是那些原产于干旱地区的橡树品种，经历了组织渗透势的变化。然而，这种变化是由物候还是干旱引起的，还有待进一步研究。所报道的体积弹性模量值在物种和研究之间差别很大，并且观察到在干旱期间以与地区或黎明前水势或渗透势的变化无关的方式增加和减少。干旱期间的昼夜叶水势可能不能很好地反映不同树种之间气体交换速率的差异，因为种间在干燥避免和耐性方面存在差异。
Most North American oaks (Quercus spp.) are adapted to drought-prone sites by an ability either to avoid, or to tolerate, water stress, or both. Generally, they have deep-penetrating root systems, enabling them to maintain relatively high predawn water potentials during drough. Oaks have thick leaves and some have relatively small stomata, both characteristics that favor high water use efficiency. However, some species, from warm regions, have large stomatal pores. The rapid evaporative cooling made possible by large stomata, may be adaptation to high temperature. Some southeastern species display leaf curling during drought, and Q. douglasii a native of California is drought deciduous. Oaks have a ring-porous xylem anatomy, allowing rapid sap movement in large diameter, early-wood vessels when soil water is plentiful, and slower, but sustained, water movement in narrower, late-wood vessels, which are more resistant to cavitation, during drought. Oaks frequently maintain a higher rate of photosynthesis at low leaf water potentials and high vapor pressure deficits than co-occurring species of other genera. An exception is Quercus rubra, which is generally restricted to relatively mesic sites. During drought, many oak species, especially those native to arid regions, undergo changes in tissue osmotic potential. However, it remains to be shown whether such changes are phenological or drought induced. Reported values for bulk modulus of elasticity vary widely among species and studies, and have been observed to both increase and decrease during drought in a way that is unrelated to region or to changes in predawn water potential or osmotic potential. Diurnal leaf water potential during drought is probably a poor indicator of differences among oak species in gas exchange rate, because of interspecific variation in desiccation avoidance and tolerance.