Olugbadieye Oloruntobi Gideon, Boucher Etienne, Deslauriers Annie, Bergeron Yves, Rosa Eric, Lemay Marc-André, Gennaretti Fabio
Institut de Recherche sur les Forêts, Groupe de Recherche en Écologie de la MRC Abitibi, Université du Québec en Abitibi-Témiscamingue, 341, Rue Principale Nord, Amos (QC), Canada J9T 2L8.
Department of Geography, GEOTOP and Centre d'études nordiques, Université du Québec à Montréal, Montréal (QC), Canada H2X 3R9.
Tree Physiol. 2025 Aug 22. doi: 10.1093/treephys/tpaf102.
Pinus banksiana exhibits remarkable ecological adaptability, thriving across diverse environments in the Canadian boreal zone, including clay deposits, fast-draining glacial tills, and rocky outcrops. However, projected rising temperature and increasing vapor pressure deficit (VPD), could increase the species' vulnerability, particularly in dry regions. In this study, we measured basal area increment (BAI) and physiological responses from isotopic fractionation across a soil gradient including three sites in the boreal mixed wood of western Quebec, Canada. The sites were a clay-rich soil (CLY, a humid site), an esker base (ESB, an intermediate site), and an esker top (EST, a sandy, well drained, dry site). Using tree-ring analysis and dual stable isotopes (δ13C and δ18O), we evaluated intrinsic water-use efficiency (iWUE) and leaf water enrichment (Δ18Olw). Our results revealed a significant correlation between Δ18Olw and VPD, indicating that stomatal regulation is the crucial physiological mechanism controlling P. banksiana's response to environmental stress across the sites. This effect was most pronounced at the dry EST site, where higher iWUE and less negative δ13C values suggest greater stomatal limitation of CO2 uptake. Increased iWUE was associated with enhanced BAI in the humid CLY site and a negative iWUE-BAI relationship emerged at EST, suggesting carbon assimilation constraints under drier conditions. Our results reveal a physiological trade-off in P. banksiana across a soil moisture gradient, demonstrating that rising atmospheric demand may decouple water-use efficiency from growth in drier environments like the EST site. By integrating isotopic signatures with growth dynamics, our study identifies a potential ecological tipping point beyond which increased iWUE may no longer sustain carbon gain under intensifying climate stress.
班克松表现出显著的生态适应性，在加拿大北方森林带的各种环境中都能茁壮成长，包括粘土沉积地、排水迅速的冰碛土和岩石露头。然而，预计气温上升和水汽压亏缺（VPD）增加，可能会增加该物种的脆弱性，特别是在干旱地区。在本研究中，我们在加拿大魁北克西部北方混交林的一个土壤梯度上，包括三个地点，测量了胸径生长量（BAI）和同位素分馏的生理响应。这些地点分别是富含粘土的土壤（CLY，一个湿润的地点）、蛇形丘底部（ESB，一个中等的地点）和蛇形丘顶部（EST，一个沙质、排水良好的干旱地点）。通过树木年轮分析和双稳定同位素（δ13C和δ18O），我们评估了内在水分利用效率（iWUE）和叶片水分富集（Δ18Olw）。我们的结果显示，Δ18Olw与VPD之间存在显著相关性，表明气孔调节是控制班克松在各地点对环境胁迫响应的关键生理机制。这种效应在干旱的EST地点最为明显，那里较高的iWUE和较小的负δ13C值表明对CO2吸收的气孔限制更大。在湿润的CLY地点，iWUE增加与BAI增强相关，而在EST地点则出现了iWUE与BAI的负相关关系，表明在较干燥条件下存在碳同化限制。我们的结果揭示了班克松在土壤湿度梯度上的生理权衡，表明大气需求增加可能会使干旱环境（如EST地点）中的水分利用效率与生长脱钩。通过将同位素特征与生长动态相结合，我们的研究确定了一个潜在的生态临界点，超过该点，在气候胁迫加剧的情况下，iWUE增加可能不再能维持碳增益。
