Trade-off between water transport efficiency and leaf life-span in a tropical dry forest
Trade-off between water transport efficiency and leaf life-span in a tropical dry forest
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热带干燥森林水输送效率和叶子寿命之间的权衡
作者：
M. Sobrado
干旱落叶和万年青树种共存于热带干旱森林。干旱落叶树种必须科普更大的季节性叶水势波动比万年青树种，这可能会增加他们对干旱引起的木质部栓塞的敏感性。测定了两组叶片的水分运输效率与叶片寿命之间的关系。木材含水量（Wc）和木材比重（G）的季节变化存在差异。在干旱季节，干旱落叶树种的Wc下降，最低值记录时，落叶完成。此时，气体的体积分数（Vg）增加，表明空气进入木质部导管。相比之下，Wc，G和Vg全年只有轻微的变化，万年青树种。干旱落叶树种的最大导水率是万年青树种的2-6倍。但在落叶时严重减少。在万年青树种，类似的水电导率在潮湿和干燥的季节。木质部的水分运输能力和叶的寿命之间的权衡发现共存于这片森林中的物种揭示了存在的对比，但成功的适应这种环境。干旱落叶树种在短期内最大限度地提高产量，具有较高的水分运输效率，导致栓塞的季节性发生。相反，万年青树种的行为降低最大效率是保守的，但安全的木质部栓塞。
Drought-deciduous and evergreen species coexist in tropical dry forests. Drought-deciduous species must cope with greater seasonal leaf water-potential fluctuations than evergreen species and this may increase their susceptibility to drought-induced xylem embolism. The relationship between water transport efficiency and leaf life-span were determined for both groups. They differed in seasonal changes of both, wood water content (Wc) and wood specific gravity (G). During the dry season, the Wc in drought-deciduous species declined and the minimum value was recorded when leaf fall was complete. At this time, the volumetric fraction of gas (Vg) increased indicating air entry into xylem vessels. In contrast, Wc, G and Vg changed only slightly throughout the year for evergreen species. Maximum hydraulic conductivity of drought-deciduous species was 2–6 times that of the evergreen species. but was severely reduced at leaf fall. In the evergreen species, similar water conductivities were measured during wet and dry seasons. The trade-off between xylem water transport capacity and leaf lifespan found in species coexisting in this forest reveals the existence of contrasting but successful adaptations to this environment. Drought-deciduous species maximize production in the short term with higher water transport efficiency which leads to the seasonal occurrence of embolisms. Conversely, the behaviour of evergreen species with reduced maximum efficiency is conservative but safe in relation to xylem embolism.