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热旱，这可能会导致森林生态系统中的高大树木受到极端的水分胁迫。树木在极端干旱下处理水分胁迫的方式还没有被很好地理解。为了应对这一挑战，这项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压力的基本问题。树木可以调整其物理结构以应对长期的水分胁迫，但地下蓄水动态如何在树木生理中引起补偿反应尚不清楚。例如，一棵面临间歇性干旱的树木是否会做出与面对常年干旱相同的生理调整？在水已经是树木生长的限制因素，而且未来可能会变得更具限制性的地方，这样的问题尤其相关。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。通过了解复杂山区的树木水分胁迫，这项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。深层“临界区”蓄水在缓解极端干旱期间森林水分胁迫方面的作用，可能会因为树木在结构和生理上适应地下水文条件的方式而受到干扰。例如，储存在深厚、高度风化的基岩中的水可能会缓解树木的季节性水分压力。然而，如果树木具有不适应的生理特征，那么在长期干旱期间，能够获得深水存储的树木可能容易受到水力故障的影响。该项目使用地震勘测和电阻率层析成像技术进行现场调查，以收集美国科罗拉多州Boulder Creek分水岭的地下结构和沿山坡横断面的水存储数据，该分水岭是动态水临界区集群网络的一部分。关于地下蓄水动态的信息将与树木生态生理测量相结合，以揭示临界地带蓄水如何影响半干旱环境中的森林干旱脆弱性和蒸腾通量。最终，这项研究寻求提高对气候条件和地下结构如何调节复杂山区地形上的水通量的机械理解。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.