Ziegler Yanick, Grote Rüdiger, Alongi Franklin, Knüver Timo, Ruehr Nadine K
Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research - Atmospheric Environmental Research (KIT/IMK-IFU), Kreuzeckbahnstraße 19, 82467 Garmisch-Partenkirchen, Germany.
Tree Physiol. 2024 Dec 16;44(12). doi: 10.1093/treephys/tpae140.
The severity of droughts is expected to increase with climate change, leading to more frequent tree mortality and a decline in forest ecosystem services. Consequently, there is an urgent need for monitoring networks to provide early warnings of drought impacts on forests. Dendrometers capturing stem diameter variations may offer a simple and relatively low-cost opportunity. However, the links between stem shrinkage, a direct expression of tree water deficit (TWD), and hydraulic stress are not well understood thus far. In this study, we exposed two widespread conifers Pinus sylvestris L. and Larix decidua Mill. to lethal dehydration by withholding water and closely monitored TWD, midday water potential ($\psi $) and midday stomatal conductance (${\textit g}{\textit s}$) under controlled greenhouse conditions. We found strong relationships between the three variables throughout the dehydration process, particularly suggesting the potential for continuous $\psi $ predictions and stomatal closure assessments. However, the relationships decoupled during recovery from severe drought. We also identified TWD thresholds that signal the onset of drought stress and tissue damage, providing insights into stress impacts and recovery potential. While these findings are promising, challenges remain in practically transferring them to field set-ups by suitable TWD normalization. Importantly, we observed that midday ${\textit g}{\textit s}$ was drastically reduced when TWD persisted overnight, providing a directly applicable drought stress signal that does not require normalization. In conclusion, while challenges remain, our results highlight the potential of dendrometers for monitoring tree water dynamics. Implementing dendrometer networks could support the development of early warning metrics for drought impacts, enabling large-scale monitoring in diverse settings, such as urban areas and forest ecosystems.
预计干旱的严重程度会随着气候变化而增加，导致树木死亡率更高，森林生态系统服务功能下降。因此，迫切需要监测网络来提供干旱对森林影响的早期预警。记录树干直径变化的测树仪可能提供了一个简单且成本相对较低的机会。然而，到目前为止，作为树木水分亏缺（TWD）直接表现的树干收缩与水力胁迫之间的联系还没有得到很好的理解。在本研究中，我们使两种广泛分布的针叶树欧洲赤松（Pinus sylvestris L.）和欧洲落叶松（Larix decidua Mill.）在可控温室条件下通过停水来承受致命脱水，并密切监测TWD、午间水势（$\psi$）和午间气孔导度（${\textit g}{\textit s}$）。我们发现在整个脱水过程中这三个变量之间存在很强的关系，特别表明了连续预测$\psi$和评估气孔关闭的潜力。然而，在从严重干旱恢复过程中这些关系解耦了。我们还确定了表明干旱胁迫和组织损伤开始的TWD阈值，为胁迫影响和恢复潜力提供了见解。虽然这些发现很有前景，但通过合适的TWD归一化将它们实际应用于野外设置仍存在挑战。重要的是，我们观察到当TWD持续一整夜时，午间${\textit g}{\textit s}$会急剧降低，这提供了一个无需归一化即可直接应用的干旱胁迫信号。总之，虽然挑战依然存在，但我们的结果突出了测树仪在监测树木水分动态方面的潜力。建立测树仪网络可以支持干旱影响早期预警指标的开发，从而在城市地区和森林生态系统等不同环境中进行大规模监测。
