Barnard Romain L, Salmon Yann, Kodama Naomi, Sörgel Karin, Holst Jutta, Rennenberg Heinz, Gessler Arthur, Buchmann Nina
Institute of Plant Sciences, ETH Zurich, 8092 Zurich, Switzerland.
Plant Cell Environ. 2007 May;30(5):539-50. doi: 10.1111/j.1365-3040.2007.01654.x.
Understanding ecosystem water fluxes has gained increasing attention, as climate scenarios predict a drier environment for many parts of the world. Evaporative enrichment of (18)O (Delta(18)O) of leaf water and subsequent enrichment of plant organic matter can be used to characterize environmental and physiological factors that control evaporation, based on a recently established mechanistic model. In a Pinus sylvestris forest, we measured the dynamics of oxygen isotopic composition (delta(18)O) every 6 h for 4 d in atmospheric water vapour, xylem sap, leaf water and water-soluble organic matter in current (N) and previous year (N-1) needles, phloem sap, together with leaf gas exchange for pooled N and N-1 needles, and relevant micrometeorological variables. Leaf water delta(18)O showed strong diel periodicity, while delta(18)O in atmospheric water vapour and in xylem sap showed little variation. The Delta(18)O was consistently lower for N than for N-1 needles, possibly related to phenological stage. Modelled leaf water Delta(18)O showed good agreement with measured values when applying a non-steady state evaporative enrichment model including a Péclet effect. We determined the time lags between delta(18)O signals from leaf water to water-soluble foliar organic matter and to phloem sap at different locations down the trunk, which clearly demonstrated the relevance of considering these time-lag effects for carbon transport, source-sink and carbon flux partitioning studies.
随着气候情景预测世界许多地区将面临更干燥的环境，了解生态系统的水分通量越来越受到关注。基于最近建立的机理模型，叶片水分的氧-18蒸发富集（δ¹⁸O）以及随后植物有机质的富集可用于表征控制蒸发的环境和生理因素。在一片樟子松林中，我们连续4天每6小时测量一次大气水汽、木质部汁液、叶片水分以及当年（N）和前一年（N-1）针叶中的水溶性有机质、韧皮部汁液的氧同位素组成（δ¹⁸O）动态，同时测量了N和N-1针叶的叶片气体交换以及相关的微气象变量。叶片水分δ¹⁸O表现出强烈的昼夜周期性，而大气水汽和木质部汁液中的δ¹⁸O变化很小。N针叶的δ¹⁸O始终低于N-1针叶，这可能与物候期有关。当应用包含佩克莱特效应的非稳态蒸发富集模型时，模拟的叶片水分δ¹⁸O与测量值显示出良好的一致性。我们确定了从叶片水分到不同树干位置的水溶性叶部有机质和韧皮部汁液的δ¹⁸O信号之间的时间滞后，这清楚地证明了在碳运输、源-库和碳通量分配研究中考虑这些时间滞后效应的相关性。
