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则倾向于从地球大气中吸收甲烷。 自2012年以来，缅因州豪兰研究森林的研究人员一直在测量这片亚寒带森林的甲烷波动。他们的研究发现，由于微生物的消耗，森林通常充当甲烷“水槽”，尽管偶尔在极端潮湿的条件下，情况可能正好相反。 这个研究地点提供了一个理想的机会来研究森林从净汇转变为大气甲烷来源的条件。在未来的气候变化情景下，预计该区域将变得更加温暖和潮湿，这种条件可能导致甲烷从汇向源转移，并有可能在区域乃至全球范围内对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如何应对气候变暖，以确定可能导致森林从甲烷汇转变为甲烷源的条件。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，包括来自科学界代表性不足群体的研究学者。将召开一系列公开讲座，并将以科学推广为重点的短视频和故事地图与“科学家在课堂上”访问当地高中配对。该项目将在豪兰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。本研究的目的是确定-通过整合的实地观察，实验室分析和建模-的条件和机制，驱动甲烷汇与源活动在森林中，使用豪兰研究森林在缅因州作为一个案例研究。该项目的新方法集中在三个关键领域，以提高对此类栖息地甲烷的理解：1）确定土壤微生物群落的作用和反应，特别是产甲烷菌和甲烷氧化菌（及其功能性的行会），在驱动甲烷通量跨越环境梯度方面的作用; 2）了解和量化湿与干景观微网站，森林中的地下和地上成分对季节性和年度甲烷通量都有贡献; 3）整合从实地和实验室分析中获得的知识，为生态系统过程模型提供信息并加以改进。一套原位和实验室为基础的实验措施，甲烷的生产和氧化，稳定同位素，和配置文件的微生物群落组成和功能将被用来了解的机制，过程和反馈驱动甲烷汇/源活动从网站到景观水平。在现场一级，将获得土壤和地上甲烷通量、微生物特征和相关现场环境条件的多尺度观测结果。为了进一步了解和量化甲烷响应，将采用原位和实验室操作实验，以确定功能性行会活动在不断变化的环境条件下调节甲烷产生/氧化以及最终进出大气的净甲烷通量的作用。最后，这些数据，与项目数据增强的微生物模型甲烷动力学双Arabius Michaels Menten（M3 D-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年豪兰森林内景观水平的季节性和年度甲烷汇/源活动。该研究将包括在本科生，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。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.