Collaborative Research: Does tree encroachment with altered hydrology in peatlands accelerate or suppress decomposition?

泥炭地是全球碳(C)循环中的重要生态系统，因为它们能够在凉爽和潮湿的条件下吸收和储存大量的碳。虽然这些条件在很长一段时间内趋于稳定，但现在正在发生巨大的变化。一些泥炭地被抽干用于农业或林业。在气候变暖的情况下，其他地区会变得更暖和、更干燥。当泥炭地被排干或干涸时，所有储存的碳会发生什么？这个复杂问题的答案需要通过真菌和其他微生物的相互作用来了解地下植被、树木生长和泥炭分解变化的影响。这个项目将使用一个大规模的实验装置来研究地下发生的变化，因为泥炭地土壤被排干，树木开始殖民。实验将测试伴随树根的地下真菌群落的变化将如何影响储存的碳的保留和分解，以及它可能以二氧化碳和甲烷等温室气体的形式释放到大气中。增加泥炭C的保留可能有助于减缓全球变暖，而温室气体的释放可能导致更大、更快的变暖。在开展研究的过程中，本项目还将为本科生和研究生提供培训机会，并扩展到高中教师和学生。泥炭地储存了全球三分之一的土壤，占地球陆地面积的三分之一。由于气候变化或排水，泥炭地C很容易被氧化。泥炭地C库通常在饱和条件下受到保护。然而，在气候变暖的情况下，许多泥炭地将变得更加干燥。虽然一般认为干燥条件会增加分解，但潜在的反馈导致长期干燥将如何改变分解轨迹的主要不确定性。例如，干旱条件已被证明有利于泥炭地木本植物群落的入侵，这可能导致分解速率的变化。与不同植物功能类群（外生菌根树、Ericaceae、莎草科）相关的真菌群落的变化在介导分解变化方面尤为重要，但我们对这些不同真菌类群如何影响原位分解的理解还很初级。本项目的总体目标是了解木本植物入侵和长期排水对泥炭地好氧和厌氧分解的抵消作用。实验将验证两个关键假设：1)树木入侵将增加排干泥炭地的分解，这是外生菌根真菌（EcMF）群落胞外酶组的功能；ii)在厌氧条件下，不同的真菌分解途径和排水历史将产生具有不同供电子和接受电子能力的泥炭。一个三向全因子实验将在一个气候可控的中环境设施中使用大型、完整的泥炭墩，操纵泥炭排水历史、地下水位位置和树木的存在。与此同时，还将进行一项田间试验，在该试验中，树木的根系通道将在排水梯度上进行控制。中观方法是本研究的关键，因此可以操纵排水历史和地下水位，从而解开水文变化的短期和长期影响。野外试验将把中观操纵的结果与自然环境条件相结合。通过对真菌群落功能变化的详细描述，以及对泥炭中氧化酶、分解、泥炭化学和“氧化还原泵”的影响，该项目将为泥炭在水文变化下的长期稳定性提供机制见解。本科生和研究生的训练将是研究目标的一部分，学生将帮助将结果传达给高中学生和教师。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。

Peatlands are important ecosystems in the global carbon (C) cycle owing to their ability to take up and store vast quantities of C under cool and wet conditions. While these conditions have tended to be stable for long periods of time, vast changes are now taking place. Some peatlands have been drained for agriculture or forestry. Others will become warmer and drier in a warming climate. What happens to all the stored C when peatlands are drained or dry up? The answer to this complex question requires understanding the impacts of changes in vegetation, tree growth and peat decomposition below ground through interactions with fungi and other microorganisms. This project will use a large-scale experimental set-up to study the changes that take place underground as peatland soils are drained and trees begin to colonize. Experiments will test how changes in the below ground fungal community accompanying tree roots will impact retention and decomposition of stored C and its potential release into the atmosphere as greenhouse gases like carbon dioxide and methane. Increased retention of peat C would potentially help mitigate global warming while release of greenhouse gases could result in even greater, faster warming. In the course of conducting the research this project will also afford training opportunities for undergraduate and graduate students and outreach to high school teachers and students.Peatlands store about 1/3 of soil C globally in 1/30th of the Earth's land area. Peatland C is vulnerable to oxidation as a result of climate change or water drainage. Peatland C stocks are generally protected under saturated conditions. However many peatlands will become drier in a warming climate. While it is generally assumed that drier conditions will increase decomposition, there are potential feedbacks that lead to major uncertainty in how long-term drying will alter the trajectory of decomposition. For example, drier conditions have been shown to favor the encroachment of woody plant communities in peatlands, which may result in changes in decomposition rates. Changes in the fungal community associated with different plant functional groups (ectomycorrhizal trees, Ericaceae, sedges) are particularly important in mediating changes in decomposition, yet our understanding of how these different fungal groups influence decomposition in situ is rudimentary. The overarching goal of this project is to understand the countervailing effects of woody plant encroachment and long-term drainage on aerobic and anaerobic decomposition in peatlands. Experiments will test two key hypotheses: i) tree encroachment will increase decomposition in drained peatlands as a function of the extracellular enzyme suite of the ectomycorrhizal fungal (EcMF) community; and ii) divergent fungal decomposer pathways and drainage histories will generate peat with differing capacity for donating and accepting electrons under anaerobic conditions. A three-way full factorial experiment will use large, intact peat pedons in a climate controlled mesocosm facility, manipulating peat drainage history, water table position, and tree presence. This will be paralleled by a field experiment in which tree root access will be manipulated over a drainage gradient. The mesocosm approach is the key to this study, so that drainage history and water tables can be manipulated, thus disentangling short- and long-term impacts of changing hydrology. The field experiment will anchor results of the mesocosm manipulations with conditions in the natural environment. Through this and detailed characterization of fungal community functional changes and consequent effects on oxidative enzymes, decomposition, peat chemistry, and "redox pumping" in peat, the project will provide mechanistic insight into the long-term stability of peat in response to altered hydrology. Undergraduate and graduate student training will be integral to the research goals, and the students will help communicate results to high school students and teachers.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.