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

该项目基于令人惊讶的初步发现，解决了一个重要问题，即落叶灌木和树木在北极生态系统水平衡中的作用。在苔原和北方森林中，大量的水在春季的短时间内（2至3周）释放，当时冬季的雪迅速融化。大部分的融雪水通过河流流出，因为在融雪过程中，地面大部分都是冻结的，而剩余的相当大一部分融雪水被认为是通过蒸发或升华损失的，或者在那些永久冻土层不阻止的地区被地下水补充。植物在一年中的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，落叶树在落叶前会吸收25-40%的融雪水，并在整个夏季从这些储存中汲取，包括在漫长的干旱期。初步数据还显示，北极落叶灌木的茎随着积雪融化而昼夜起伏，研究人员怀疑这与水分吸收有关，但灌木含水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意义，从水分平衡到气候反馈，再到干旱期落叶植被的应对策略。世纪在阿拉斯加观察到的落叶灌木和树木的扩张可能会以目前尚未考虑的方式改变水平衡和北极生态系统。调查人员问：落叶植被（树木和灌木）在多大程度上利用融雪水？落叶乔木和灌木的扩张对北方生态系统的生态水文学有什么影响？融雪水的储存和使用对植物生态有什么影响（如对天气变化的缓冲）？他们建议在阿拉斯加的气候梯度上描述灌木和树木的生理学（吸水，水分胁迫，蒸腾，生长，光合作用）以及环境变量，包括融雪。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对融雪水吸收的控制，并量化融雪水在干旱期间维持生理活动的作用。该提案通过量化落叶植物对融雪水通道和水库的作用，并通过评估储存融雪水在干旱期缓冲植被的潜力，解决了生态水文学的新途径。拟议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。考虑到观察到的落叶树木和灌木的广泛扩张以及观察到的融雪日期的提前，这种重新考虑是突出的。该项目将支持两名早期职业调查员，一名博士生和3名本科生。几个不同的推广活动，建议，包括教师研讨会，旨在提高当地和农村阿拉斯加K-12教室的科学课程，一个巡回博物馆展览，艺术展览的主要PI的工作，并与科学作家的合作伙伴关系，全州范围内传播的一篇文章，每年在全州（阿拉斯加）的新闻媒体。

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.