Postdoctoral Fellowship: EAR-PF: How Does Critical Zone Water Storage Impact Forest Drought Stress Across Complex Terrain?

气候变化正在导致更频繁的高温干旱，这可能导致森林生态系统中高大树木的极度缺水。在极端干旱的情况下，树木应对水分压力的方式尚不清楚。为了应对这一挑战，本研究将解决有关地下储存的水如何影响树木生长和生理水分胁迫的基本问题。树木可以调整其物理结构来应对慢性水分胁迫，但目前尚不清楚地下水储存动态如何导致树木生理上的代偿反应。例如，面对间歇性干旱的树木是否会做出与面对常年干旱的树木相同的生理调整？在水已经成为树木生长限制因素的地方，这样的问题尤其重要，而且在未来可能会变得更加限制。这项研究将在美国科罗拉多州进行，由于气候变暖，那里的山地森林积雪正在减少。通过了解复杂山区地形中树木的水分胁迫，本研究的结果将广泛适用于寻求提高森林抗旱能力和确保水资源可持续管理的科学家和森林管理者。在极端干旱期间，深层“临界带”储水在缓解森林水资源压力方面的作用可能会被树木对地下水文条件的结构和生理适应方式所混淆。例如，储存在深层、高度风化的基岩中的水可以减轻树木的季节性水分压力。然而，如果树木有不适应的生理特征，那么在长期干旱期间，能够获得深水储存的树木可能容易遭受水力破坏。该项目采用基于现场的调查，利用地震调查和电阻率层析成像技术，收集美国科罗拉多州博尔德溪流域山坡横断面地下结构和储水量的数据，这是动态水临界带集群网络的一部分。地下储水动态信息将与树木生态生理测量相结合，揭示临界区储水如何影响半干旱环境下森林干旱脆弱性和蒸腾通量。最终，本研究旨在提高对气候条件和地下结构如何调节复杂山区地形的水通量的机制理解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Climate change is causing more frequent hot droughts, which can lead to extreme water stress for tall trees in forest ecosystems. The ways that trees deal with water stress under extreme drought are not well understood. To address this challenge, this research will address fundamental questions about how water stored below ground affects tree growth and physiological water stress. Trees can adapt their physical structure to deal with chronic water stress, but it is unclear how subsurface water storage dynamics do or do not lead to compensatory responses in tree physiology. For example, will a tree faced with intermittent drought make the same physiological adjustments as those faced with perennial drought? Questions like these are particularly relevant in places where water is already a limiting factor for tree growth and could become more limiting in the future. This study will take place in Colorado, USA, where snowpack in montane forests is declining due to climate warming. By understanding tree water stress across complex mountainous terrain, the results of this study will be broadly relevant for scientists and forest managers seeking to improve forest drought resilience and ensure sustainable management of water resources. The role of deep “critical zone” water storage in mitigating forest water stress during extreme drought may be confounded by the way trees adapt structurally and physiologically to subsurface hydrological conditions. For example, water stored in deep, highly weathered bedrock may mitigate seasonal water stress in trees. However, trees with access to deep water storage may be vulnerable to hydraulic failure during prolonged drought if they have maladapted physiological traits. This project employs field-based investigations using seismic surveys and electrical resistivity tomography to gather data on belowground structure and water storage along hillslope transects in the Boulder Creek Watershed in Colorado, USA, part of the Dynamic Water Critical Zone Cluster Network. Information on subsurface water storage dynamics will be combined with tree ecophysiological measurements to reveal how critical zone water storage influences forest drought vulnerability and transpiration fluxes in semi-arid environments. Ultimately, this research seeks to improve mechanistic understanding of how climatic conditions and subsurface structure regulate water fluxes across complex mountainous terrain.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.