Research Unit Forest Dynamics, Swiss Federal Institute for Forest Snow and Landscape Research WSL, Zürcherstrasse 111, 8903, Birmensdorf, Switzerland.
Institute of Terrestrial Ecosystems, Swiss Federal Institute of Technology ETH, Universitaetsstrasse 16, 8092, Zurich, Switzerland.
New Phytol. 2022 Oct;236(1):58-70. doi: 10.1111/nph.18224. Epub 2022 Jun 21.
The impact of climate extremes on forest ecosystems is poorly understood but important for predicting carbon and water cycle feedbacks to climate. Some knowledge gaps still remain regarding how drought-related adjustments in intra-annual tree-ring characteristics directly impact tree carbon and water use. In this study we quantified the impact of an extreme summer drought on the water-use efficiency and carbon sequestration of four mature Norway spruce trees. We used detailed observations of wood formation (xylogenesis) and intra-annual tree-ring properties (quantitative wood anatomy and stable carbon isotopes) combined with physiological water-stress monitoring. During 41 d of tree water deficit, we observed an enrichment in C but a reduction in cell enlargement and wall-thickening processes, which impacted the anatomical characteristics. These adjustments diminished carbon sequestration by 67% despite an 11% increase in water-use efficiency during drought. However, with the resumption of a positive hydric state in the stem, we observed a fast recovery of cell formation rates based on the accumulated assimilates produced during drought. Our findings enhance our understanding of carbon and water fluxes between the atmosphere and forest ecosystems, providing observational evidence on the tree intra-annual carbon sequestration and water-use efficiency dynamics to improve future generations of vegetation models.
极端气候对森林生态系统的影响还不太清楚，但对于预测碳和水的循环对气候的反馈非常重要。关于干旱如何直接影响树木的碳和水分利用，年轮特征的年内调整，我们仍有一些知识空白。在这项研究中，我们量化了一次极端夏季干旱对四棵成熟挪威云杉的水分利用效率和碳固存的影响。我们使用详细的木材形成（木质部形成）和年内年轮特性（定量木材解剖结构和稳定碳同位素）的观测结果，结合生理水分胁迫监测。在 41 天的树木水分亏缺期间，我们观察到 C 的富集，但细胞扩大和细胞壁加厚过程减少，这影响了解剖特征。尽管干旱期间水分利用效率提高了 11%，但这些调整减少了 67%的碳固存。然而，随着树干中积极水分状态的恢复，我们观察到基于干旱期间产生的积累同化产物的细胞形成速率的快速恢复。我们的研究结果增强了我们对大气和森林生态系统之间碳和水通量的理解，为改善未来植被模型提供了关于树木年内碳固存和水分利用效率动态的观测证据。
