Tundra ecosystem responses to 30 years of experimental and observed changes in climate

冻土带生态系统对最近的气候变化表现出强烈的反应。国际冻土带实验（ITEX）等协调的分布式实验为这些系统如何响应实验和观测到的气候变化以及整个冻土带生物群系的响应变化提供了关键知识。1992年，我在埃尔斯米尔岛高北极地区的七个不同冻土带群落中建立了第一套ITEX研究，并继续进行实验。每个站点都有透明的开顶室（OTCs）的升温处理，在单个站点，升温与营养物添加和雪操作相结合。在接下来的5年里，我将结束这些实验，并利用这个独特的机会来测量冻土带系统对实验结束的反应。研究生和博士后将进行实地研究，并利用现场30多年研究的广泛数据库来回答将植物性状与群落和生态系统变化联系起来的问题，以测试苔原植物适应变暖气候的能力，并确定长期的操纵是否从根本上改变了苔原系统。在温暖的土地上的植物一直表现出较早的物候，生长和繁殖的努力和成功，特别是那些开花早的植物。此外，随着少数优势物种盖度的增加和多样性的增加，其组成和丰度也发生了变化。然而，我们尚未将这些性状的响应性与样地生物多样性的变化联系起来，这将有助于更好地预测植被的变化。学生将使用所有测量物种的特征数据来探索这些联系。这些基于性状的研究将为植物性状的时间变异性提供最早的评估之一。近30年来，暖样区夏季温度比环境温度高1 ~ 3℃，1992年以来环境温度也升高了2℃。学生将帮助确定实验和控制地块之间的差异轨迹，在去除处理后继续。在研究的第二年，50%的otc将被移除，并在接下来的三年里进行回应，以检查系统对环境条件的“放松”。将在植物水平上测量响应（例如物候、繁殖努力和成功以及光合作用）；群落水平，包括组成和丰度的变化；生态系统水平，包括养分有效性和吸收量、CO2净生态系统交换和样地光谱特征的测量。在计划研究的第五年，我们将在样地进行破坏性收获，以确定地上和地下生物量（NPP）和植物性状的变化。这些实验的苦乐参半的结局将为苔原生态系统的持续变化提供持续的关键知识。

Tundra ecosystems have shown strong responses to recent changes in climate. Coordinated distributed experiments such as the International Tundra Experiment (ITEX) have provided critical knowledge on how these systems respond to experimental and observed changes in climate and the response variation across the tundra biome. I established the first set of ITEX studies in 1992 in seven different tundra communities at a High Arctic site on Ellesmere Island and continue to maintain the experiments. Each site has a warming treatment of transparent open-top chambers (OTCs), and in single sites warming is combined with nutrient addition and snow manipulation. Over the next 5 years, I will bring the experiments to an end and use this unique opportunity to measure the response of tundra systems to the termination of the experiments. Graduate students and postdocs will conduct field studies and use the extensive data base from the 30+ years of research at the site to answer questions linking plant traits to community and ecosystem change, to test the ability of tundra plants to adapt to a warming climate and the determine if the long-term manipulations have fundamentally altered the tundra systems. Plants in the warmed plots have consistently shown advanced phenology and increased growth and reproductive effort and success, especially those that flower early. In addition, the composition and abundance has shifted with increased cover of a few dominant species but also greater diversity. However, we have yet to link the responsiveness of the traits to the changes in biodiversity in the plots, and this will lead to better predictions of vegetation change. Students will explore these links using trait data from all of the species measured. These trait-based studies will provide one of the first assessments of temporal variability in plant traits. The warmed plots have been 1-3ºC above the ambient summer temperature for 30 years, and the ambient temperature has also increased by 2ºC since 1992. Students will help determine the trajectory of the differences between experimental and control plots continue after the treatments are removed. In the second year of the study, 50 % of the OTCs will be removed and responses followed over the next three years to examine the "relaxation" of the system to ambient conditions. Responses will be measured at the plant level (e.g., phenology, reproductive effort and success, and photosynthesis); the community level, including changes in composition and abundance; and the ecosystem level, including measurements of nutrient availability and uptake, net ecosystem exchange of CO2, and spectral characteristics of the plots. In the fifth year of the proposed study, we will conduct destructive harvests in the plots to determine changes in above and below-ground biomass (NPP) and plant traits. The bitter sweet end to these experiments will provide continued critical knowledge of tundra ecosystems as they continue to change.