Thomas Anaïs, Marron Nicolas, Bonal Damien, Piutti Séverine, Dallé Erwin, Priault Pierrick
Université de Lorraine, AgroParisTech, INRAE, UMR Silva, 54000 Nancy, France.
Université de Lorraine, INRAE, UMR Laboratoire Agronomie et Environnement (LAE), 54518 Vandœuvre-lès-Nancy, France.
Tree Physiol. 2022 Dec 12;42(12):2432-2445. doi: 10.1093/treephys/tpac094.
In a global context where water will become a scarce resource under temperate latitudes, managing tree plantations with species associations, i.e., forest mixture or agroforestry, could play a major role in optimizing the sustainable use of this resource. Conceptual frameworks in community ecology suggest that, in mixed plantations, environmental resources such as water may be more efficiently used for carbon acquisition and tree growth thanks to niche complementarity among species. To test the hypotheses behind these conceptual frameworks, we estimated water-use efficiency (WUE) for poplar trees grown in a monoculture, in association with alder trees (forest mixture) and in association with clover leys (agroforestry) in an experimental plantation located in northeastern France. Water-use efficiency was estimated (i) at leaf level through gas exchange measurements and analysis of carbon isotope composition, (ii) at wood level through carbon isotope composition and (iii) at tree level with sap flow sensors and growth increment data. We hypothesized that species interactions would increase WUE of poplars in mixtures due to a reduction in competition and/or facilitation effects due to the presence of the N2-fixing species in mixtures. Poplar trees in both mixture types showed higher WUE than those in the monoculture. The differences we found in WUE between the monoculture and the agroforestry treatment were associated to differences in stomatal conductance and light-saturated net CO2 assimilation rate (at the leaf level) and transpiration (at the tree level), while the differences between the monoculture and the forest mixture were more likely due to differences in stomatal conductance at the leaf level and both transpiration and biomass accumulation at the tree level. Moreover, the more WUE was integrated in time (instantaneous gas exchanges < leaf life span < seasonal wood core < whole tree), the more the differences among treatments were marked.
在全球范围内，温带地区的水资源将变得稀缺，利用物种组合来管理人工林，即森林混交或农林业，可能在优化这种资源的可持续利用方面发挥重要作用。群落生态学的概念框架表明，在混交人工林中，由于物种间的生态位互补性，水等环境资源可能会更有效地用于碳获取和树木生长。为了验证这些概念框架背后的假设，我们在法国东北部的一个试验人工林中，估算了单一种植的杨树、与桤木混交（森林混交）以及与三叶草草地混交（农林业）的杨树的水分利用效率（WUE）。通过以下方式估算水分利用效率：（i）在叶片水平，通过气体交换测量和碳同位素组成分析；（ii）在木材水平，通过碳同位素组成；（iii）在树木水平，使用液流传感器和生长增量数据。我们假设，由于混交林中固氮物种的存在减少了竞争和/或促进作用，物种间的相互作用会提高混交林中杨树的水分利用效率。两种混交类型中的杨树均显示出比单一种植的杨树更高的水分利用效率。我们发现单一种植与农林业处理之间水分利用效率的差异与气孔导度和光饱和净二氧化碳同化率（叶片水平）以及蒸腾作用（树木水平）的差异有关，而单一种植与森林混交之间的差异更可能是由于叶片水平的气孔导度以及树木水平的蒸腾作用和生物量积累的差异。此外，水分利用效率在时间上整合得越多（瞬时气体交换<叶片寿命<季节性木芯<整棵树），处理之间的差异就越明显。
