Collaborative Research: Understanding biophysical drivers of the CH4 source sink transition in Northern Forests

甲烷对人类引起的气候变化的贡献仅次于二氧化碳，因为它的全球变暖潜力是二氧化碳的34倍。潮湿环境中的微生物倾向于释放甲烷，而干燥环境中的微生物倾向于从地球大气中吸收气体。缅因州豪兰研究森林的研究人员自2012年以来一直在测量这片亚北方森林的甲烷波动。他们的研究发现，由于微生物的消耗，森林通常是甲烷的“汇”，尽管在极端潮湿的条件下，偶尔也会出现相反的情况。这个研究地点提供了一个理想的机会来研究在什么条件下，森林将从一个净汇转变为大气甲烷的来源。在未来气候变化的情况下，该区域预计将变得更加温暖和潮湿，这种情况可能会导致甲烷从汇到源的转变，并有可能对区域乃至全球范围内的大气甲烷浓度产生影响。该项目将研究森林土壤微生物群落将如何应对气候变暖，以确定可能导致森林从甲烷汇转变为更多来源的条件。该项目还将支持对研究生和本科生以及博士后研究学者进行跨学科培训，包括那些来自科学领域代表性不足群体的学生。将召开一系列公众讲座，并将重点放在科学推广的短视频和StoryMaps与对当地高中的访问相匹配。该项目将在霍兰德研究森林为学生和公众举办一个开放日，以了解这项重要的研究。本研究旨在通过野外观测、实验室分析和模拟相结合的方法，以缅因州豪兰研究森林为例，确定驱动森林中甲烷汇与源活动的条件和机制。该项目的新方法侧重于三个关键领域，以提高对这类生境中甲烷的了解：1)确定土壤微生物群落，特别是产甲烷菌和甲烷养殖菌(及其功能集团)在推动跨环境梯度甲烷通量方面的作用和反应；2)了解和量化森林中潮湿和干燥景观微站点以及地下和地上部分如何对季节性和年度甲烷通量作出贡献；以及3)整合从现场和实验室分析中获得的知识，以提供信息和改进生态系统过程模型。将使用一套甲烷产生和氧化的现场和实验室实验方法、稳定同位素以及微生物群落组成和功能的剖面来了解从场地到景观水平驱动甲烷汇/源活动的机制、过程和反馈。在场地一级，将获得对土壤和地上甲烷通量、微生物特征以及相关的现场环境条件的多尺度观测。为了进一步了解和量化甲烷反应，将采用现场和实验室操作实验，以确定在不断变化的环境条件下，功能性行会活动在调节甲烷产生/氧化和最终进出大气的净甲烷通量方面的作用。最后，这些数据与项目数据--增强的甲烷动力学微生物模型--双重Arrhenius Michaels Menten(M3D-DAMM)和社区土地模型-微生物(CLM-Microbe)过程模型相结合，将使研究人员能够确定从现在到2100年豪兰森林内景观层面的季节性和年度甲烷汇/源活动。这项研究将包括本科生、研究生和博士后水平的培训，以及各种外展活动，以吸引高中生和公众。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Methane is second only to carbon dioxide in its contribution to human-induced climate change due to its global warming potential, which is 34 times greater than that of CO2. Microorganisms in wet landscapes tend to release methane, whereas those in dry ones tend to take up the gas from Earth's atmosphere. Researchers at the Howland Research Forest in Maine have been measuring methane fluctuations across this sub-boreal forest since 2012. Their studies have found that the forest usually serves as a methane "sink" due to microbial consumption, although occasionally, under extremely wet conditions, the reverse can be true. This research site provides an ideal opportunity to study the conditions under which a forest would switch from a net sink to become a source of atmospheric methane. Under future climate change scenarios, the region is expected to become warmer and wetter, conditions that may induce a shift from methane sink to source, with the potential to have an impact on atmospheric methane concentrations at regional to global scale. This project will examine how forest soil microbial communities will change in response to climate warming, to identify the conditions that may lead forests to switch from being a methane sink to more of a source. The project will also support the cross-disciplinary training of graduate and undergraduate students and postdoctoral research scholars, including those from underrepresented groups in science. A series of public talks will be convened, and short videos and StoryMaps focused on science outreach will be paired with “scientist in the classroom” visits to local high schools. The project will host an open house for students and the public at the Howland Research Forest to learn about this important research. This study aims to identify - through the integration of field observations, laboratory analyses, and modeling - the conditions and mechanisms driving methane sink vs source activity in forests, using the Howland Research Forest in Maine as a case study. The project's novel approach focuses on three key areas to improve understanding of methane in such habitats: 1) identify the roles and response of soil microbial communities, specifically, methanogens and methanotrophs (and their functional guilds), in driving methane flux across environmental gradients; 2) understand and quantify how wet vs dry landscape microsites, and belowground vs. aboveground components within a forest contribute to seasonal and annual methane fluxes; and 3) integrate knowledge gained from field and laboratory analyses to inform and improve ecosystem process models. A suite of in-situ and lab-based experimental measures of methane production and oxidation, stable isotopes, and profiles of microbial community composition and function will be used to understand the mechanisms, processes, and feedbacks driving methane sink/source activity from site to landscape levels. At the site level, multi-scale observations of soil and aboveground methane fluxes, microbial traits, and associated in-situ environmental conditions will be obtained. To further understand and quantify methane response, in-situ and laboratory manipulation experiments to identify the role of functional guild activity, under changing environmental conditions, in regulating methane production/oxidation and ultimately net methane flux to and from the atmosphere will be employed. Finally, these data, integrated with project data-enhanced Microbial Model for Methane Dynamics-Dual Arrhenius Michaels Menten (M3D-DAMM) and Community Land Model-Microbe (CLM-Microbe) process models, will allow researchers to identify seasonal and annual methane sink/source activity at the landscape level within Howland Forest from the present to 2100. The research will include training at the undergraduate, graduate and postdoctoral levels, as well as a variety of outreach activities to engage high school students and the public.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.