Collaborative Research: Winter snow depth as a driver of microbial activity, nutrient cycling, tree growth and treeline advance in the Arctic

北极树线的位置是气候和生存资源的重要调节器。 主要研究人员（PI）最近的研究表明，冬季积雪深度对树木生长的控制非常重要。 他们现在建议通过实验来分离积雪深度和土壤养分对树木生长的重要性。 这一新颖的跨学科建议将微生物生态学与大规模景观模式联系起来。 如果他们的假设得到证实，这些发现将与当时流行的树线位置原因理论相矛盾。本项目将通过支持培养三名研究生和吸引众多本科生参与研究活动，为科学人才的发展做出贡献。 对主要是阿拉斯加土著社区的Kotzebue的宣传将采取不同的形式。 PI将与当地广播电台（当地媒体沟通的主要手段）安排，以描述他们的研究。 他们将参观当地的高中，讨论植被在气候中的作用，并分享他们的研究成果。 他们将为当地高中的优秀学生提供参加实地研究计划的机会。 他们会参加土地管理局吗？的坎贝尔溪科学中心炉边聊天系列，以促进推广到更多的城市社区和周围的安克雷奇，AK。 他们将加强现有的交互式树叶分解模型（IMOLD），这是一系列关于分解和营养循环的动画课程和活动，是在以前的奖项下开发的，包括来自北极树线这项工作的例子和教学活动。长期以来，人们一直认为温度直接控制树线树木的生长和树线的位置。 然而，PI？最近在北极对白色云杉的研究表明，温度对土壤养分有效性的间接影响可能具有同等或更大的重要性。 他们假设，树木线上寒冷的土壤，特别是在冬季，限制了微生物的活动和养分的供应，使树木几乎无法生存和生长。 在冬季进行的测量显示，北极森林保持的积雪比在树线上观察到的要深得多。 树木被认为可以捕获积雪，导致积雪更深，使土壤与冷空气隔绝，并允许更大的越冬微生物活动和更大的营养矿化。 事实上，PI发现白色云杉的生长和冬季积雪深度之间存在很强的正相关性。 他们建议通过使用雪栅栏来控制冬季积雪深度和肥料来分离这种相关性的机制，以增加土壤水分不同的三条树木的土壤养分可用性。 为了提供一个实验测试的重要性，温度作为一个直接控制树木生长，他们建议将实验拍摄变暖到他们的雪栅栏实验中的析因设计。 他们预测，实验性的降雪和营养添加将导致微生物活动、光合作用、树木生长、种子质量、种子生产、幼苗建立和新树木的招募大幅增加。 他们希望在土壤潮湿和寒冷的地方观察到最大的积极反应。与此同时，他们预测芽温将导致生长的变化可以忽略不计。

The position of the Arctic treeline is an important regulator of climate and subsistence resources. Recent research by the principal investigators (PIs) suggests the importance of winter snow depth as a control on tree growth. They now propose to experimentally isolate the importance of snow depth and soil nutrient availability for tree growth. This novel and interdisciplinary proposal will link the ecology of microbes to large-scale landscape patterns. If their hypotheses are confirmed, the findings will contradict the prevailing theory of the cause of treeline location.This project will contribute to the development of the science workforce by supporting the training of three graduate students and the entrainment of numerous undergraduate students into the research activities. Outreach to the predominantly Alaskan Native community of Kotzebue will take different forms. The PIs will arrange with the local radio station, a primary means of media communication for the local region, to describe their research. They will visit the local high school to discuss the role of vegetation in climate and to share the results of their research. They will provide opportunities for outstanding students from the local high school to participate in their field research program. They will participate in the Bureau of Land Management?s Campbell Creek Science Center Fireside Chat series to promote outreach to the more urban community in and around Anchorage, AK. They will enhance the existing Interactive Model of Leaf Decomposition (IMOLD), a series of animated lessons and activities about decomposition and nutrient cycling developed under a previous award, to include examples and teaching activities derived from this work at the Arctic treeline.It has long been thought that temperature exerts a direct control on growth of treeline trees and the position of the treeline. However, the PIs? recent work in the Arctic with white spruce suggests that indirect effects of temperature on soil nutrient availability may be of equal or greater importance. They hypothesize that cold soils at the treeline, particularly during winter, limit microbial activity and nutrient availability to the point where trees are barely able to survive and grow. Measurements made during winter have revealed that Arctic forests maintain snowpacks that are much deeper than observed at treeline. Trees are thought to trap snow and lead to a deeper snowpack, insulating the soil from cold air and allowing for greater overwinter microbial activity and greater nutrient mineralization. Indeed, the PIs found a strong positive correlation between white spruce growth and winter snow depth. They propose to isolate the mechanisms underlying this correlation by using snowfences to manipulate winter snow depth and fertilizer to increase soil nutrient availability at three treelines that differ in soil moisture. To provide an experimental test of the importance of temperature as a direct control on treeline tree growth, they propose to incorporate experimental shoot warming into their snowfence experiment in a factorial design. They predict that both experimental snow and nutrient additions will lead to large increases in microbial activity, photosynthesis, tree growth, seed quality, seed production, seedling establishment and recruitment of new trees. They expect to observe the greatest positive responses where soils are wet and cold. Meanwhile, they predict that shoot warming will lead to negligible changes in growth.