Nilsen E T, Sharifi M R, Rundel P W, Forseth I N, Ehleringer J R
Biology Department, Virginia Polytechnic Institute and State University, 24061, Blacksburg, VA, USA.
LBES, University of California, 900 Veteran Avenue, 90024, Los Angeles, CA, USA.
Oecologia. 1990 Mar;82(3):299-303. doi: 10.1007/BF00317474.
Water relations of several stem succulent trees were measured in north-central Baja California in comparisons to other growth forms in the same habitat. Our research concentrated on three stem succulent species (Idria collumnaris, Pachycormus discolor and Bursera microphylla) each with a different succulent stem morphology. The stem succulent trees had 1 to 4 kg HO/m of trunk while the other trees and shrubs in the same habitat had 0.6 to 0.8 kg HO/m. The diurnal and seasonal variation in leaf water potential was small for the stem succulent species in comparison to deciduous and evergreen species as a consequence of the stem-water, buffering capacity. In addition, the leaf conductance of the stem succulent species was low (60 mmol m s) and yet, the leaf conductance decreased through the day similar to adjacent evergreen and deciduous species. The leaves of the stem succulent trees lost turgor at low saturated water deficits (0.06 to 0.14), had comparatively high osmotic potentials, and high values of elastic modulus in comparison to adjacent evergreen and deciduous species. The stem acts as an important buffering mechanism allowing for the maintenance of leaf turgor in these stem succulent trees. The low transpiration rates of the stem succulent trees may be a mechanism to minimize leaf saturated water deficit and extend leaf longevity.
在墨西哥下加利福尼亚州中北部，对几种茎肉质树木的水分关系进行了测量，并与同一栖息地的其他生长形式进行了比较。我们的研究集中在三种茎肉质物种（柱状伊德里亚树、变色厚茎树和小叶裂榄）上，每种都有不同的肉质茎形态。茎肉质树木的树干每米有1至4千克水，而同一栖息地的其他树木和灌木每米有0.6至0.8千克水。由于茎的水分缓冲能力，与落叶和常绿物种相比，茎肉质物种的叶水势的昼夜和季节变化较小。此外，茎肉质物种的叶导度较低（60 mmol m⁻² s⁻¹），然而，其叶导度在一天中与相邻的常绿和落叶物种一样下降。与相邻的常绿和落叶物种相比，茎肉质树木的叶子在低饱和水分亏缺（0.06至0.14）时失去膨压，具有相对较高的渗透势和较高的弹性模量值。茎起到了重要的缓冲机制作用，使这些茎肉质树木能够维持叶膨压。茎肉质树木的低蒸腾速率可能是一种将叶饱和水分亏缺降至最低并延长叶片寿命的机制。
