Physiological regulation and efficient xylem water transport regulate diurnal water and carbon balances of tropical lianas
Physiological regulation and efficient xylem water transport regulate diurnal water and carbon balances of tropical lianas
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生理调节和有效的木质部水运输调节热带藤本植物的昼夜水和碳平衡
DOI：
10.1111/1365-2435.12724
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发表时间：
2017-02-01
影响因子：
5.2
通讯作者：
Cao, Kun-Fang
中科院分区：
文献类型：
--
作者：
Chen, Ya-Jun;Schnitzer, Stefan A.;Cao, Kun-Fang
1. 热带藤本植物的大部分叶子朝向森林冠层的顶部，而树木的树冠则更分层。森林树冠经常暴露在炎热和多风的条件下，藤本植物如何应对这些环境下极高的蒸腾需求仍然未知。研究了中国西南热带森林中4种藤本植物的茎水力特性、叶片耐旱性、叶片和茎水势（psi（叶片）和psi（茎））、气孔导度（g(s)）、光合速率、液流和茎原生电导率损失率（PLC）的日变化。选择5种共发生树种进行比较。与共生的树木相比，藤本植物在相对较低的蒸汽压亏缺（< 1 kPa）下达到最大蒸腾，表明上午光合作用旺盛。然而，藤本植物在一天中明显下降，中午和下午的g(s)较低。藤本植物一般具有较高的茎材比电导率和最大液通量密度，但对干旱引起的空化的耐受性不如常绿树木。藤本植物和乔木在正午时都失去了冠层顶部的叶片膨胀，但藤本植物比乔木更早（约2小时）失去叶片膨胀。当木质部张力释放至-0.3至-0.5 MPa时，8个物种中有7个物种的PLC在中午增加。平均而言，藤本植物在白天经历了较高的PLC(35.9%)，叶片和茎间水势的不平衡程度比树木更大（δ psi（茎叶）：1.37 MPa对0.75 MPa）。较早的气孔关闭和有效的水分输送可能有助于藤本植物保持比树木更高的psi（茎），尽管它们具有相似的psi（叶）。我们的研究结果为热带藤本植物的生理调节和有效的水分输送调节日常水分关系提供了证据，并可能解释藤本植物如何在热带季节性森林中有效地运作。需要对更广泛的物种进行进一步的研究来证实我们的发现。
1. Tropical lianas deploy most of their leaves towards the top of the forest canopy, whereas trees exhibit a more stratified crown. Forest canopies are often exposed to hot and windy conditions, and how lianas cope with the extremely high transpirational demands under these environments remains unknown.2. We investigated stem hydraulic properties, leaf drought tolerance, diurnal changes in leaf and stem water potentials (psi(leaf) and psi(stem)), stomatal conductance (g(s)), photosynthetic rate, sap flow and stem native percentage loss of conductivity (PLC) for four liana species in a tropical forest in southwest China. Five co-occurring tree species were also selected for comparison.3. Lianas reached maximal transpiration at a relatively lower vapour pressure deficit (< 1 kPa) than did co-occurring trees, suggesting vigorous photosynthesis during the morning. However, liana gs declined markedly over the day, with low g(s) at midday and afternoon. Lianas generally had higher stem sapwood-specific conductivity and maximum sap flux density but were less tolerant to drought-induced cavitation than were evergreen trees. Both lianas and trees lost leaf turgor in the top canopy at midday, but lianas lost leaf turgor earlier (similar to 2 h) than trees.4. Seven of eight species exhibited midday increases in PLC when xylem tensions were released to -0.3 to -0.5 MPa for PLC measurements. On average, lianas experienced high PLC (35.9%), along with a greater degree of disequilibrium between leaf and stem water potentials than trees (Delta psi(stem-leaf): 1.37 MPa vs. 0.75 MPa) during the day. Earlier stomatal closure and efficient water transport may help lianas maintain higher psi(stem) than trees despite having similar psi(leaf).5. Our results provide evidence that physiological regulation and efficient water transport mediate daily water relations in tropical lianas and may explain how lianas operate efficiently in tropical seasonal forests. Further studies involving a broader range of species are needed to confirm our findings.