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

北极林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，冬季积雪深度作为控制树木生长的重要因素。他们现在提议通过实验分离出积雪深度和土壤养分有效性对树木生长的重要性。这项新颖的跨学科提案将把微生物生态与大规模的景观格局联系起来。如果他们的假设得到证实，这些发现将与目前流行的树线定位原因理论相矛盾。该项目将支持三名研究生的培训和无数本科生参与研究活动，从而促进科学队伍的发展。对以阿拉斯加原住民为主的Kotzebue社区的外联将采取不同的形式。PIS将与当地广播电台安排，描述他们的研究情况。广播电台是当地主要的媒体传播手段。他们将访问当地的一所高中，讨论植被在气候中的作用，并分享他们的研究结果。他们将为当地高中的优秀学生提供参与他们的实地研究项目的机会。他们将参加土地管理局？S坎贝尔溪科学中心炉边聊天系列活动，以促进与安克雷奇及其周围更多城市社区的接触。他们将增强现有的树叶分解互动模型(IMOLD)，这是一系列关于分解和养分循环的动画课程和活动，是在之前的奖项下开发的，包括北极树线上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的生长和树线的位置。然而，私家侦探？最近在北极对白云杉的研究表明，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，林线上的寒冷土壤，特别是在冬天，会限制微生物的活动和养分的可获得性，以至于树木几乎无法生存和生长。冬季进行的测量显示，北极森林的积雪比在树线上观察到的要深得多。树木被认为能困住积雪，导致积雪更深，使土壤免受冷空气的影响，并允许更多的越冬微生物活动和更多的营养矿化。事实上，PI发现白云杉的生长与冬季积雪深度之间存在很强的正相关关系。他们建议通过使用雪栅栏来控制冬季积雪深度和化肥，以增加土壤水分不同的三条树线上的土壤养分有效性，从而分离出这种相关性背后的机制。为了对温度作为树木生长的直接控制的重要性提供实验测试，他们建议将实验枝条变暖纳入他们的雪栅栏实验中，采用析因设计。他们预测，实验降雪和营养添加都将导致微生物活动、光合作用、树木生长、种子质量、种子产量、幼苗建立和新树招募的大幅增加。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，嫩芽变暖将导致可以忽略不计的生长变化。

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.