Chapotin Saharah Moon, Razanameharizaka Juvet H, Holbrook N Michele
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
Plant Cell Environ. 2006 Jun;29(6):1021-32. doi: 10.1111/j.1365-3040.2005.01456.x.
Baobab trees are often cited in the literature as water-storing trees, yet few studies have examined this assumption. We assessed the role of stored water in buffering daily water deficits in two species of baobabs (Adansonia rubrostipa Jum. and H. Perrier and Adansonia za Baill.) in a tropical dry forest in Madagascar. We found no lag in the daily onset of sap flow between the base and the crown of the tree. Some night-time sap flow occurred, but this was more consistent with a pattern of seasonal stem water replenishment than with diurnal usage. Intrinsic capacitance of both leaf and stem tissue (0.07-0.08 and 1.1-1.43 MPa(-1), respectively) was high, yet the amount of water that could be withdrawn before turgor loss was small because midday leaf and stem water potentials (WPs) were near the turgor-loss points. Stomatal conductance was high in the daytime but then declined rapidly, suggesting an embolism-avoidance strategy. Although the xylem of distal branches was relatively vulnerable to cavitation (P50: 1.1-1.7 MPa), tight stomatal control and minimum WPs near--1.0 MPa maintained native embolism levels at 30-65%. Stem morphology and anatomy restrict water movement between storage tissues and the conductive pathway, making stored-water usage more appropriate to longer-term water deficits than as a buffer against daily water deficits.
猴面包树在文献中常被引述为储水树，但很少有研究检验这一假设。我们评估了马达加斯加热带干燥森林中两种猴面包树（红皮猴面包树和巴氏猴面包树）中储存水在缓冲每日水分亏缺方面的作用。我们发现，树基部和树冠之间的液流每日开始时间没有滞后。夜间有一些液流发生，但这更符合季节性树干水分补充模式，而非昼夜用水模式。叶片和茎组织的固有电容（分别为0.07 - 0.08和1.1 - 1.43 MPa(-1)）较高，但在膨压丧失前能够提取的水量较少，因为中午叶片和茎的水势接近膨压丧失点。白天气孔导度较高，但随后迅速下降，这表明存在避免栓塞的策略。尽管远端树枝的木质部相对容易发生空化（P50：1.1 - 1.7 MPa），但紧密的气孔控制和接近 - 1.0 MPa的最低水势使天然栓塞水平维持在30 - 65%。茎的形态和解剖结构限制了储存组织与传导途径之间的水分移动，使得储存水的利用更适合长期水分亏缺，而非作为每日水分亏缺的缓冲。
