Boreal soil carbon: the stable, the labile, and the unknown

北方森林土壤是世界上最大的陆地碳库。因此，北方碳储量和碳通量的变化可能会对全球碳循环产生重大影响。这些北部的高纬度土壤也非常容易受到全球变暖的影响，预计在未来一个世纪，平均气温将大幅上升，冻融模式将发生变化，植被将发生变化。北方土壤中的碳是一个由相互关联的池组成的复杂网络，其稳定性可能受到不同机制的控制。因此，预测北方土壤碳对环境变化的反应一直是具有挑战性的。我的长期研究目标是量化潜在的环境因素如何控制土壤中有机质的积累和分布。通过这项拟议的研究计划，我计划阐明土壤地质材料和植被之间的相互作用可能最终决定北方土壤碳对气候变化的反应。我将通过以下方式应对这一挑战：1.量化在十年时间尺度上周转的两个碳库(地下和森林地面)的来源、形成途径和稳定性；2.研究环境变化如何改变通过不稳定的(生物和根际)碳库的碳通量，以及这可能如何影响后续的碳积累途径和稳定性。我将培训三名博士生和两名MSC学生，以及几名本科生研究助理。学生项目将是独立的，但又是相互关联的。这些项目的重点是了解各种环境因素，包括总体变暖、冻融循环的变化和植被的变化，将如何影响以下四个北方碳库：1.地下土壤碳--我们将调查土壤地质材料如何控制深层碳的来源和稳定性；2.森林地面碳--我们将专注于更深层次的腐殖化有机质层中的碳，并调查这种碳在某些情况下可能比深层矿物碳更稳定的可能性；3.生物碳--我们将研究植被变化如何通过具有代表性的北方森林的土壤生物群落影响碳通量；4.根际碳--我们将研究根际(根影响区)如何影响分解代谢和合成代谢过程中微生物碳通量的分配。来自加拿大各地的各种北方森林将被包括在这个计划中。这将允许从广泛的地质材料、森林类型和气候来表征土壤有机质。该计划将结合合理的土壤学领域方法、受控环境室内的同位素标记实验和最先进的分析方案。其结果将是对有机质转化途径的前所未有的表征，这将从根本上促进我们对北方土壤中碳积累和稳定性的理解。总体而言，这项研究计划将建立改善北方土壤碳对气候变化响应的预测所需的基础科学知识。这反过来将为管理和适应战略提供信息，这些战略是为维持北方森林生态系统而量身定做的。

Boreal forest soils are the single largest terrestrial carbon storehouse in the world. Consequently, changes in boreal carbon stocks and fluxes could significantly affect the global carbon cycle. These northern, high-latitude soils are also highly susceptible to global warming, and in the coming century are expected to face large increases in average temperatures, altered freeze-thaw patterns, and transformative vegetation shifts. The carbon contained in boreal soils is a complex network of interconnected pools whose stability may be controlled by different mechanisms. As such, it has been challenging to predict the response of boreal soil carbon to environmental changes. My long-term research objective is to quantify how the underlying environmental factors control organic matter accumulation and distribution in soils. With this proposed research program, I plan to clarify how interactions between the soil geological material and vegetation may ultimately determine the response of boreal soil carbon to climatic changes. I will address this challenge by:1. Quantifying the sources, formation pathways, and stability of two carbon pools (subsurface and forest floor) that turn over on a decadal time scale; 2. Investigating how carbon fluxes through labile (biological and rhizosphere) carbon pools may be altered by environmental changes, and how this may affect subsequent carbon accumulation pathways and stability.I will be training three PhD and two Msc students, as well as several undergraduate research assistants. Student projects will be independent yet interlinked. The focus of these projects is to understand how various environmental factors, including overall warming, changes in freeze-thaw cycles, and vegetation shifts, will affect the following four boreal carbon stores: 1. Subsurface soil carbon-- We will investigate how soil geological material may control the source and stability of carbon present at depth;2. Forest floor carbon-- We will focus on the carbon present within the deeper, humified organic matter layer, and investigate the possibility that this carbon may, in some cases, be more stable than deep mineral carbon;3. Biological carbon-- We will look at how vegetation changes affect carbon fluxes through soil biological communities in representative boreal forests;4. Rhizosphere carbon-- We will examine how the rhizosphere (zone of root influence) affects the partitioning of microbial carbon fluxes between catabolic and anabolic processes.A variety of boreal forests from across Canada will be included in this program. This will allow for characterization of soil organic matter from wide ranges of geological materials, forest stand types, and climate. The program will combine a sound pedological field approach, isotope labelling experiments in controlled-environment chambers, and state-of-the-art analytical protocols. The result will be an unprecedented characterization of organic matter transformation pathways, which will fundamentally advance our understanding of carbon accumulation and stability in boreal soils. Overall, this research program will establish the foundational scientific knowledge required to improve prediction of boreal soil carbon response to climate change. This will, in turn, inform management and adaptation strategies that are tailor-made for sustaining boreal forest ecosystems.