INRA, UMR Ecologie des Forêts de Guyane, Campus Agronomique, BP 709, 97387, Kourou Cedex, French Guiana.
Oecologia. 2013 Dec;173(4):1191-201. doi: 10.1007/s00442-013-2724-6. Epub 2013 Jul 14.
Though the root biomass of tropical rainforest trees is concentrated in the upper soil layers, soil water uptake by deep roots has been shown to contribute to tree transpiration. A precise evaluation of the relationship between tree dimensions and depth of water uptake would be useful in tree-based modelling approaches designed to anticipate the response of tropical rainforest ecosystems to future changes in environmental conditions. We used an innovative dual-isotope labelling approach (deuterium in surface soil and oxygen at 120-cm depth) coupled with a modelling approach to investigate the role of tree dimensions in soil water uptake in a tropical rainforest exposed to seasonal drought. We studied 65 trees of varying diameter and height and with a wide range of predawn leaf water potential (Ψpd) values. We confirmed that about half of the studied trees relied on soil water below 100-cm depth during dry periods. Ψpd was negatively correlated with depth of water extraction and can be taken as a rough proxy of this depth. Some trees showed considerable plasticity in their depth of water uptake, exhibiting an efficient adaptive strategy for water and nutrient resource acquisition. We did not find a strong relationship between tree dimensions and depth of water uptake. While tall trees preferentially extract water from layers below 100-cm depth, shorter trees show broad variations in mean depth of water uptake. This precludes the use of tree dimensions to parameterize functional models.
尽管热带雨林树木的根系生物量集中在上层土壤中，但深根系对土壤水分的吸收已被证明对树木蒸腾作用有贡献。精确评估树木尺寸与水分吸收深度之间的关系，将有助于基于树木的建模方法，预测热带雨林生态系统对未来环境条件变化的响应。我们使用了一种创新的双重同位素标记方法（表层土壤中的氘和 120 厘米深处的氧），并结合建模方法，研究了在季节性干旱条件下，树木尺寸在热带雨林土壤水分吸收中的作用。我们研究了 65 棵直径和高度不同、且具有广泛的黎明前叶片水势（Ψpd）值的树木。我们证实，在干旱期间，大约一半的研究树木依赖于 100 厘米以下深度的土壤水分。Ψpd 与水分提取深度呈负相关，可以作为该深度的大致替代指标。一些树木在水分吸收深度上表现出相当大的可塑性，表现出一种有效的适应策略，用于获取水和养分资源。我们没有发现树木尺寸与水分吸收深度之间存在很强的关系。虽然高树优先从 100 厘米以下的深度提取水分，但矮树在平均水分吸收深度上表现出广泛的变化。这排除了使用树木尺寸来参数化功能模型的可能性。
