LTREB: Following the reorganization and resynchronization of biogeochemical cycles after an unprecedented tundra fire

阿拉斯加林木线以北的北极苔原正以全球最快的速度对全球变暖做出反应。这些反应包括植物生长加快、下层永久冻土解冻、微生物活动增加导致土壤碳流失、野火发生频率和严重程度增加。从历史上看，低温使冻土带火灾相对不常见。但预计到2100年，气候变暖将影响北极地区的火灾规模和频率增加一倍。火灾通过燃烧植被和土壤上的死有机质层，影响苔原提供的生态系统服务长达数十年至数百年。由于植被在火灾后通过一个被称为演替的过程迅速重新定居在景观中，其组成发生了变化，碳和相关营养物质（如氮和磷）的循环也发生了变化。事实上，火灾带走了植被再生和恢复所需的大部分营养物质，同时，由于绝缘有机层也被去除，土壤温度升高。温暖的土壤可能会增加土壤养分的有效性，并随着时间的推移导致从草到灌木的转变。但目前尚不清楚这些变化是否大到足以抵消火灾期间最初的碳和营养损失，这是该项目试图回答的主要问题。除了科学成果，还将制作一个在线纪录片系列，解释气候变化和火灾对北极生态系统的影响。在以前的项目中制定的专门针对居住在阿拉斯加北坡和印第安纳州的土著和少数民族人口的正式外联计划也将得到加强。该项目将在2007年有记录以来最大的北极冻土带火灾——阿纳克图伍克河火灾中，沿着扰动严重程度梯度，在三个地点建立火灾后碳和养分循环的多年代代性记录和数学模型。现有的涡动相关系统将用于继续测量2008年开始的碳和能量通量，以及土壤室。2011年对不同烧伤严重程度的土壤和生物量进行了定量采集。火灾后从草地到以灌木为主的苔原的轨迹应该创造一个积极的气候反馈，并通过降低反照率产生变暖效应。该项目将用于创建碳、氮和磷通量和储量的多年代际记录，以参数化、验证和测试应用于北极冻土带生物地球化学的多元素限制（MEL）模型。

The arctic tundra north of the tree line in Alaska is responding to the most rapid rates of warming on the globe. The responses include increased plant growth, thaw of the underlying permafrost, loss of soil carbon through increased microbial activity, and increased frequency and severity of wildfires. Historically, low temperatures have kept tundra fires as relatively infrequent events. But warming is anticipated to impact the fire regime by doubling fire size and frequency in the arctic by the year 2100. Fires impact ecosystem services provided by the tundra for decades to centuries by burning the vegetation and the layer of dead organic matter on top of the soil. As vegetation rapidly recolonizes the landscape after a fire through a process known as succession, its composition changes, as do the cycles of carbon and associated nutrients, like nitrogen and phosphorus. In fact, fires remove a large portion of nutrients needed to fuel the regrowth and recovery of vegetation, while at the same time, increase soil temperatures because the insulating organic layer has also been removed. Warmer soils may increase soil nutrient availability and lead a shift from grasses to shrubs over time. But it is unclear whether these changes are large enough to offset the initial carbon and nutrient losses during the fires, which is the main question this project seeks to answer. Besides the scientific results, an online documentary series will be produced that explains the effects of climate change and fire on arctic ecosystems. Formal outreach programs developed in prior projects that specifically address indigenous and minority populations living on the North Slope in Alaska and in Indiana will also be enhanced.This project will develop a multi-decadal record and mathematical model of post-fire carbon and nutrient cycling across three sites along a disturbance severity gradient within the largest recorded arctic tundra fire, the Anaktuvuk River fire from 2007. An existing eddy covariance system will be used to continue measurements of carbon and energy fluxes begun in 2008, along with soil chambers. A quantitative soil and biomass harvest was conducted in 2011 across a burn severity gradient. Post-fire trajectories from grass to shrub-dominated tundra should create a positive climatic feedback and produce a warming effect through decreased albedo. This project will be used to create a multi-decadal record of carbon, nitrogen and phosphorus fluxes and stocks to parameterize, validate, and test the Multiple Element Limitation (MEL) model as applied to the biogeochemistry of arctic tundra.