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

由于甲烷的全球变暖潜能值是二氧化碳的34倍，它对人类引起的气候变化的贡献仅次于二氧化碳。湿润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，森林通常起到甲烷“汇”的作用，尽管偶尔，在极端潮湿的条件下，相反的情况也可能发生。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，预计该地区将变得更加温暖和潮湿，这些条件可能导致甲烷从汇向源的转变，并有可能对区域到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如何响应气候变暖而发生变化，以确定可能导致森林从甲烷汇转变为甲烷源的条件。该项目还将支持研究生和本科生以及博士后研究学者的跨学科培训，包括来自科学领域代表性不足群体的学者。将召开一系列的公开演讲，并将把以科学推广为重点的短视频和故事地图与对当地高中的“科学家在课堂上”访问结合起来。该项目将在豪兰研究森林为学生和公众举办开放日，以了解这项重要的研究。本研究以缅因州的Howland研究森林为例，旨在通过实地观测、实验室分析和建模相结合，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，以提高对此类栖息地甲烷的认识：1)确定土壤微生物群落，特别是产甲烷菌和氧化甲烷菌（及其功能行会）在推动甲烷通量跨环境梯度中的作用和响应；2)了解和量化森林内湿润与干燥景观微点、地下与地上组分对季节性和年度甲烷通量的贡献；3)整合从现场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和改进。一套基于原位和实验室的甲烷生成和氧化实验测量、稳定同位素、微生物群落组成和功能剖面将用于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。在场地水平上，将获得土壤和地上甲烷通量、微生物特征和相关的原位环境条件的多尺度观测。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来确定在不断变化的环境条件下，功能协会活动在调节甲烷产生/氧化以及最终调节大气净甲烷通量中的作用。最后，将这些数据与项目数据增强的甲烷动力学微生物模型- dual Arrhenius Michaels Menten （M3D-DAMM）和社区土地模型-微生物（clm -微生物）过程模型相结合，将使研究人员能够确定从现在到2100年Howland森林景观水平上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，以及各种推广活动，以吸引高中生和公众。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.