Quantifying and modeling the effects of deciduous shrubs and trees on the water balance of Arctic ecosystems

这个项目基于令人惊讶的初步发现，解决了一个重要的问题，即落叶灌木和乔木在北极生态系统水平衡中的作用。在苔原和北方森林中，冬季积雪迅速融化时，春季会在很短的时间(2到3周)内释放大量水分。这些融雪水中的大部分流经河流，因为在融雪过程中，地面大多是冻结的，而剩余的相当大一部分融雪水被认为是通过蒸发或升华失去的，或者是在永久冻土不能阻止的地区的地下水补给。植物在每年这个时候的吸收和储存被认为是可以忽略不计的。来自阿拉斯加内陆一个小流域的初步数据显示，落叶树在整个夏天，包括在漫长的干旱时期，都会从这些商店中吸取积雪前融化水的25%-40%。初步数据还显示，随着积雪融化，北极落叶灌木茎昼夜起伏，调查人员怀疑这与水分吸收有关，但灌木水分含量与积雪融化之间的联系尚不清楚。落叶乔木和灌木的水分吸收具有重要的生态系统影响，从水平衡到气候反馈，再到干旱时期落叶植被的应对策略。在20世纪观察到的阿拉斯加落叶灌木和树木的扩张很可能正在以目前尚未被考虑的方式改变水平衡和北极生态系统。研究人员问：落叶植物(树木和灌木)在多大程度上使用融雪水？落叶乔木和灌木的扩展对北方生态系统的生态水文学有何影响？储存和使用融雪水的植物生态后果(如缓解气候变化的影响)是什么？他们建议对阿拉斯加不同气候梯度的灌木和树木的生理特性(水分吸收、水分胁迫、蒸腾作用、生长、光合作用)以及包括融雪在内的环境变量进行表征。这些数据将被整合到统计模型中，这些模型将量化树木和灌木吸收融雪水的控制，并将量化融雪水在干旱时期维持生理活动方面的作用。该提案涉及新出现的生态水文学途径，方法是量化落叶植物在融雪水的路径和水库中的作用，并评估储存的融雪水在干旱时期缓冲植被的潜力。拟议工作的变革性在于重新考虑植被在融雪水文过程中扮演次要角色的教条。考虑到观察到的落叶乔木和灌木的广泛扩展以及观察到的提前融雪日期，这种重新考虑是突出的。该项目将支持两名早期职业调查人员、一名博士生和三名本科生。提议开展几项不同的外联活动，包括举办教师讲习班，以加强阿拉斯加当地和农村的K-12课堂的科学课程；举办博物馆巡回展览；举办艺术展，展示主要的非政府组织的作品；与一名科学作家结成伙伴关系，每年在全州(阿拉斯加)的新闻媒体上传播一篇文章。

This project addresses an important question, based on surprising preliminary findings, about the role of deciduous shrubs and trees in the water balance of Arctic ecosystems. In the tundra and boreal forest, large amounts of water are released during a short period (2 to 3 weeks) in spring when the winter's snow rapidly melts. Most of this snowmelt water flows out through rivers, because the ground is mostly frozen during snowmelt, while the remaining sizable fraction of snowmelt water is thought to be lost through evaporation or sublimation, or to groundwater recharge in those areas where permafrost doesn't prevent it. Uptake and storage by plants at this time of year has been considered negligible. Preliminary data from a small watershed in interior Alaska shows that deciduous trees take up 25-40% of the snowmelt water prior to leaf out and draw from these stores throughout the summer, including during lengthy dry periods. Preliminary data also show that arctic deciduous shrub stems rise and fall diurnally as the snow melts, which the investigators suspect is linked with water uptake, but the link between shrub water content and snowmelt is unknown. Water uptake by deciduous trees and shrubs has important ecosystem implications, from the water balance to climate feedbacks to coping strategies of deciduous vegetation during dry periods. The observed expansion of deciduous shrubs and trees in Alaska during the 20th century is likely altering the water balance and Arctic ecosystem in ways currently not being considered.The investigators ask: To what extent do deciduous vegetation (trees and shrubs) use snowmelt water? What are the consequences of deciduous tree and shrub expansion on the ecohydrology of northern ecosystems? What are the plant ecological consequences (such as buffering from weather variability) of the storage and use of snowmelt water? They propose to characterize shrub and tree physiology (water uptake, water stress, transpiration, growth, photosynthesis), as well as environmental variables, including snowmelt, across a climate gradient in Alaska. These data will be integrated into statistical models that will quantify the controls on snowmelt water uptake by trees and shrubs, and will quantify the role of snowmelt water in sustaining physiological activity during dry periods. The proposal addresses emerging avenues of ecohydrology by quantifying the role of deciduous plants on the pathways and reservoirs of snowmelt water, and by assessing the potential for stored snowmelt water to buffer vegetation during dry periods. The transformative nature of the proposed work lies in reconsidering the dogma that vegetation plays a minor role in snowmelt hydrological processes. This reconsideration is salient given the observed widespread expansion of deciduous trees and shrubs and observed advancing snowmelt dates. The project would support two early career investigators, a PhD student, and 3 undergraduate students. Several distinct outreach activities are proposed, including teacher workshops aimed at enhancing the science curriculum of local and rural Alaskan K-12 classrooms, a traveling museum exhibit, an art exhibit featuring the work of the lead PI, and a partnership with a science writer for statewide dissemination of one article per year in statewide (Alaska) news outlets.