Motzer Thomas, Munz Nicole, Küppers Manfred, Schmitt Dieter, Anhuf Dieter
University of Mannheim, Department of Physical Geography, L9, 1-2, D-68131 Mannheim, Germany.
Tree Physiol. 2005 Oct;25(10):1283-93. doi: 10.1093/treephys/25.10.1283.
We investigated tree water relations in a lower tropical montane rain forest at 1950-1975 m a.s.l. in southern Ecuador. During two field campaigns, sap flow measurements (Granier-type) were carried out on 16 trees (14 species) differing in size and position within the forest stand. Stomatal conductance (g(s)) and leaf transpiration (E(l)) were measured on five canopy trees and 10 understory plants. Atmospheric coupling of stomatal transpiration was good (decoupling coefficient Omega = 0.25-0.43), but the response of g(s) and E(l) to the atmospheric environment appeared to be weak as a result of the offsetting effects of vapor pressure deficit (VPD) and photosynthetic photon flux (PPF) on g(s). In contrast, sap flow (F) followed these atmospheric parameters more precisely. Daily F depended chiefly on PPF sums, whereas on short time scales, VPD impeded transpiration when it exceeded a value of 1-1.2 kPa. This indicates an upper limit to transpiration in the investigated trees, even when soil water supply was not limiting. Mean g(s) was 165 mmol m(-2) s(-1) for the canopy trees and about 90 mmol m(-2) s(-1) for the understory species, but leaf-to-leaf as well as tree-to-tree variation was large. Considering whole-plant water use, variation in the daily course of F was more pronounced among trees differing in size and crown status than among species. Daily F increased sharply with stem diameter and tree height, and ranged between 80 and 120 kg day(-1) for dominant canopy trees, but was typically well below 10 kg day(-1) for intermediate and suppressed trees of the forest interior.
我们在厄瓜多尔南部海拔1950 - 1975米的低地热带山地雨林中研究了树木的水分关系。在两次野外考察期间，对林分内16棵（14种）大小和位置不同的树木进行了液流测量（Granier型）。对5棵冠层树木和10株林下植物测量了气孔导度（g(s)）和叶片蒸腾作用（E(l)）。气孔蒸腾的大气耦合良好（解耦系数Ω = 0.25 - 0.43），但由于蒸汽压亏缺（VPD）和光合光子通量（PPF）对g(s)的抵消作用，g(s)和E(l)对大气环境的响应似乎较弱。相比之下，液流（F）更精确地跟随这些大气参数。每日F主要取决于PPF总和，而在短时间尺度上，当VPD超过1 - 1.2 kPa时，它会阻碍蒸腾作用。这表明在所研究的树木中，即使土壤水分供应不受限制，蒸腾作用也存在上限。冠层树木的平均g(s)为165 mmol m(-2) s(-1)，林下物种约为90 mmol m(-2) s(-1)，但叶片间以及树木间的变化很大。考虑到整株植物的水分利用，在大小和树冠状态不同的树木之间，F的日变化过程中的差异比物种间更为明显。每日F随茎直径和树高急剧增加，优势冠层树木的日F范围在80至120千克/天之间，但森林内部的中间层和受压树木通常远低于10千克/天。
