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

基于令人惊讶的初步发现，该项目解决了一个重要的问题，即落叶灌木和树木在北极生态系统水平衡中的作用。在冻土带和北方森林，在春季冬季积雪迅速融化的短时间内（2到3周），大量的水被释放出来。大部分融雪水通过河流流出，因为在融雪期间地面大部分被冻结，而剩下的相当大一部分融雪水被认为通过蒸发或升华损失，或者在永久冻土无法阻止的地区重新补给地下水。植物在每年这个时候的吸收和储存被认为是微不足道的。来自阿拉斯加内陆一个小流域的初步数据显示，落叶树在落叶之前吸收了25-40%的融雪水，并在整个夏季（包括漫长的干旱期）从这些融雪水中吸取水分。初步数据还显示，北极的落叶灌木茎在雪融化时每天都在上升和下降，研究人员怀疑这与水分吸收有关，但灌木含水量与融雪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意义，从水分平衡到气候反馈，再到落叶植被在干旱时期的应对策略。在20世纪观测到的阿拉斯加落叶灌木和树木的扩张很可能以目前尚未考虑到的方式改变了水平衡和北极生态系统。研究者问：落叶植被（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张对北方生态系统的生态水文有什么影响？融雪水的储存和使用对植物生态的影响（如对天气变化的缓冲作用）是什么？他们建议描述灌木和树木的生理特征（水分吸收、水分胁迫、蒸腾、生长、光合作用），以及阿拉斯加气候梯度上的环境变量，包括融雪。这些数据将被整合到统计模型中，以量化对树木和灌木吸收融雪水的控制，并量化融雪水在干旱时期维持生理活动中的作用。该提案通过量化落叶植物在融雪水通道和水库中的作用，并通过评估储存融雪水在干旱时期缓冲植被的潜力，解决了生态水文学的新兴途径。所提出的工作的变革性质在于重新考虑植被在融雪水文过程中起次要作用的教条。考虑到观测到的落叶乔木和灌木的广泛扩张以及观测到的融雪日期提前，这种重新考虑是显著的。该项目将支持两名早期职业研究者、一名博士生和三名本科生。提出了几个不同的推广活动，包括旨在加强阿拉斯加当地和农村K-12教室的科学课程的教师讲习班，巡回博物馆展览，以首席PI的作品为特色的艺术展览，以及与科学作家合作，每年在全州（阿拉斯加）新闻媒体上发布一篇文章。

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.