Collaborative Research: The Changing Seasonality of Tundra Nutrient Cycling: Implications for Ecosystem and Arctic System Functioning

合作研究：苔原养分循环的季节性变化：对生态系统和北极系统功能的影响

• 批准号: 0902102
• 负责人: Edward Rastetter
• 金额: $ 18.09万
• 依托单位: Marine Biological Laboratory
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-01 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0902102&HistoricalAwards=false
• 关键词: Collaborative; Research; Changing; Seasonality; Tundra

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Abstract Arctic soils have large stores of carbon (C) and may act as a significant CO2 source with warming. However, the key to understanding tundra soil processes is nitrogen (N), as both plant growth and decomposition are severely N limited. However, current models of tundra ecosystems and their responses to climate change assume that while N limits plant growth, C limits decomposition. In addition, N availability is strongly seasonal with relatively high availability early in the growing season followed by a pronounced crash. There is a need to understand the controls on this seasonality to predict Arctic System responses to climate change, but there are multiple questions that need answers: 1) What causes the seasonal nutrient crash? 2) Does microbial activity switch seasonally between C and N limitation? 3) How will a lengthening of the growing season alter overall ecosystem C and N dynamics, as a result of differential extension of the periods before and after the nutrient crash? 4) What will be the larger impacts of these patterns on the Arctic system? Addressing these questions requires following plant and soil dynamics in a very tight time frame, coupling this understanding of the timing of C and N interactions to an enhanced mechanistic understanding of why the nutrient crash occurs, and then using transect sampling and ecosystem modeling to explore the large-scale implications of this seasonal crash. This proposed research will address our questions by: 1) Varying the length and timing of the growing season in the field by advancing snow melt and warming the ecosystem; 2) Establishing the fine scale seasonal time-courses of soil N availability, plant N content, leaf expansion, root growth and rhizodeposition, ecosystem respiration, microbial biomass and enzyme activity; 3) Conducting lab experiments to determine the extent to which microbial activity is limited by temperature, and C and N availability before and after the crash; 4) Determining how the timing of the nutrient crash and plant growth vary across a latitudinal transect; 5) Refining the Multiple Element Limitation model (MEL) that was developed for arctic ecosystems to better handle how plant and microbial systems respond to N limitation, and incorporating the specific drivers of the crash into MEL; 6) Testing the large-scale spatial and temporal effects of the seasonality of nutrient availability and how it may change in a warming Arctic with a lengthening growing season. This work will require intense mechanistic research focusing on transitions and transformations that occur over only a few weeks at most, but which have profound impacts on the tundra ecosystem. Researchers will scale this mechanistic work to the intermediate spatial scale by conducting transect measurements along a latitudinal transect to validate that patterns that occur locally are robust. They will scale to the whole Arctic system by integrating these mechanisms, and importantly, the N-effects on decomposition, into the MEL model that is designed to explore multiple limiting resource effects on ecosystem function. As an integrated package, this research will explore how the changing seasonal pattern that drives the crash in N availability in tundra soils will alter overall tundra C-cycling and its role as a source or sink of C and through this its role in the global climate system.

该奖项是根据2009年《美国复苏与再投资法》（公法111-5）资助的。抽象的北极土壤具有大量的碳（C）储存，并且可以充当带有变暖的重要二氧化碳来源。但是，理解苔原土壤过程的关键是氮（N），因为植物的生长和分解都受到严重限制。但是，当前的苔原生态系统模型及其对气候变化的反应假设，尽管n限制了植物的生长，但c限制了分解。此外，N的可用性是强烈的季节性，在生长季节的初期相对较高，随后发生了明显的崩溃。有必要了解这种季节性的控制，以预测北极系统对气候变化的反应，但是有多个需要答案的问题：1）是什么原因导致季节性营养崩溃？ 2）微生物活性在C和N限制之间是否在季节性转换？ 3）生长季节的延长将如何改变整体生态系统C和N动力学，这是由于营养崩溃前后的时期差异而导致的？ 4）这些模式对北极系统的更大影响会有什么？解决这些问题需要在非常紧密的时间范围内跟随植物和土壤动态，将对C和N相互作用的时机的理解与增强的机械理解，以了解营养崩溃的原因，然后使用横断面采样和生态系统建模来探索这种季节性崩溃的大规模含义。这项拟议的研究将通过以下方式解决我们的问题：1）通过推进雪融化和变暖生态系统来改变现场生长季节的长度和时机； 2）建立土壤n可用性，植物N含量，叶片膨胀，根部生长和根茎沉积，生态系统呼吸，微生物生物量和酶活性的精细季节性时间表； 3）进行实验室实验以确定微生物活性受温度限制的程度，以及崩溃前后的C和N可用性； 4）确定养分崩溃和植物生长的时间如何在纬度样带上变化； 5）完善为北极生态系统开发的多元元素限制模型（MEL），以更好地处理植物和微生物系统如何响应N限制，并将崩溃的特定驱动因素纳入MEL； 6）测试养分可用性季节性的大规模空间和时间影响，以及随着生长季节的延长，它如何在变暖的北极变化。这项工作将需要强烈的机械研究，重点是最多几周的过渡和转变，但对苔原生态系统产生了深远的影响。研究人员将通过沿纬度样带进行横切测量，以验证局部发生的模式，从而将这项机械工作扩展到中间空间尺度。它们将通过整合这些机制，以及重要的是，将分解的N效率扩展到整个北极系统中，该机制旨在探索对生态系统功能的多重限制资源影响。作为一项综合软件包，这项研究将探讨如何在苔原土壤中驱动n次崩溃的季节性变化将如何改变整个苔原c-cycling及其作为C来源或C的作用，以及通过其在全球气候系统中的作用。