Digging into the "Gadgil effect": how the competitive balance between fungal guilds affects carbon and nitrogen cycling

深入探讨“加吉尔效应”：真菌行会之间的竞争平衡如何影响碳氮循环

• 批准号: NE/W005816/1
• 负责人: Mark Tibbett
• 金额: $ 63.13万
• 依托单位: University of Reading
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FW005816%2F1
• 关键词: Digging; into; Gadgil; effect; how

Forest soils are part of the solutions to global climate change by sequestering carbon (C) to compensate for anthropogenic CO2 emissions, which are the major cause of rising global temperatures. Soil C-sequestration depends on two contrasting processes: soil organic matter (SOM) decomposition which results in C-loss, and SOM stabilisation that results in C-storage by converting C-containing biomolecules into decay-resistant particles. Decomposition processes are primarily controlled by the free-living saprotrophic (ST) soil fungi. These fungi gain C (energy) for their metabolism by decomposing SOM. Another group of soil organisms are root dwelling symbiotic ectomycorrhizal (EM) fungi that obtain C from their association with trees, and explore the soil for other nutrients such as nitrogen and phosphorus. As EM fungi have a C supply from trees most have lost their enzymatic capabilities to acquire C from SOM degradation, as this is not an imperative for their nutrition. As ST and EM fungi are both forest soil-borne organisms they interact and compete, particularly for soil nutrients. This competitive interaction may result in suppression of SOM decomposition (under EM dominance) as the EM fungi do not need to breakdown SOM for carbon but do rapidly acquire soil nutrients such as N and P. The observed effect that causes the suppression of SOM decomposition as these fungal types compete is known as the "Gadgil effect". If true, this phenomenon controls CO2 release from soil during decomposition and consequently offers one of the few options for climate change mitigation through enhanced C sequestration in soils. However, the mechanism by which ST and EM fungi interact in C cycling remains controversial and poorly understood, with an inconsistent evidence-base. In our project, we propose to determine whether the interactions between ST and EM fungi could be a neglected component of forest soil ecology that may be manipulated to augment soil C-sequestration in forests.For the last half of the century, since the Gadgil effect was posited, the prevailing view has been that the group of EM or ST fungi act as a whole. However, recent genetic studies suggest a high functional diversity among EM fungi, indicating it would be wrong to treat them as one group. This may well explain why numerous contradictory findings of Gadgil effect have been reported in the scientific literature. Our new understanding of abundant functions in the metabolism of EM fungi as a group opens new avenues of interrogating and finally confirming the existence (or otherwise) of the Gadgil effect. We intend to identify the mechanisms that lead to alteration of soil C-sequestration due to ST and EMF fungal interactions: e.g. increasing the dominance of certain EM fungi may lead to an increase in the creation of stable SOM in forest soils. In this way, the soil mycota may be able to be harnessed as a managed component in mitigating global climate change. In this proposal, we specifically address 3 fundamental questions: (1) What is the role of ST-EM fungal interactions in SOM decomposition and stabilisation? (2) Does the evolutionary origin and functional ecology of fungal taxa effect their interactions on SOM dynamics? (3) What are the mechanisms operating in communities in regard to ST-EM interactions under different environmental conditions? We have selected four distinct fungal groups, each of them consisting of one EM fungus paired with the closest related ST species. We designed a robust model system to quantitatively address the functional effect of fungal interactions on SOM decomposition and stabilisation. Our experimental plan includes four levels of complexity that sequentially validate the findings of ST-EM fungal interactions: (1) fungal cultures on growth-media, (2) microcosms, where EM fungi are in symbiosis with the plant, (3) mesocosms with forest tree seedlings, and (4) field sites differing in tree species and soil N availability.

森林土壤通过固碳（C）来补偿人为二氧化碳排放，是全球气候变化解决方案的一部分，而人为二氧化碳排放是全球气温上升的主要原因。土壤碳封存取决于两个截然不同的过程：土壤有机质 (SOM) 分解导致碳损失，SOM 稳定通过将含碳生物分子转化为耐腐颗粒而实现碳储存。分解过程主要由自由生活的腐生（ST）土壤真菌控制。这些真菌通过分解 SOM 来获得代谢所需的 C（能量）。另一类土壤生物是根部共生外生菌根 (EM) 真菌，它们从与树木的联系中获取碳，并探索土壤中的其他营养物质，如氮和磷。由于 EM 真菌从树木获得碳供应，大多数真菌已经失去了从 SOM 降解中获取碳的酶促能力，因为这对于它们的营养来说并不是必需的。由于 ST 和 EM 真菌都是森林土生生物，因此它们相互作用并竞争，特别是在土壤养分方面。这种竞争性相互作用可能会导致 SOM 分解的抑制（在 EM 主导下），因为 EM 真菌不需要分解 SOM 来获取碳，而是快速获取土壤养分，如 N 和 P。观察到的当这些真菌类型竞争时导致 SOM 分解受到抑制的效应被称为“Gadgil 效应”。如果属实，这种现象可以控制土壤分解过程中二氧化碳的释放，从而为通过增强土壤固碳来缓解气候变化提供了少数选择之一。然而，ST 和 EM 真菌在 C 循环中相互作用的机制仍然存在争议，人们对其知之甚少，证据基础不一致。在我们的项目中，我们建议确定 ST 和 EM 真菌之间的相互作用是否可能是森林土壤生态中被忽视的组成部分，可以通过操纵它们来增加森林中的土壤碳封存。在本世纪后半叶，自从提出 Gadgil 效应以来，普遍的观点是 EM 或 ST 真菌作为一个整体发挥作用。然而，最近的遗传学研究表明 EM 真菌具有高度的功能多样性，这表明将它们视为一组是错误的。这很好地解释了为什么科学文献中报道了许多相互矛盾的加吉尔效应发现。我们对 EM 真菌作为一个群体的代谢中的丰富功能的新认识开辟了质疑并最终确认 Gadgil 效应存在（或其他）的新途径。我们打算确定由于 ST 和 EMF 真菌相互作用而导致土壤碳封存改变的机制：例如增加某些 EM 真菌的优势可能会导致森林土壤中稳定 SOM 的产生增加。通过这种方式，土壤真菌可以作为缓解全球气候变化的受管理组成部分。在本提案中，我们具体解决了 3 个基本问题：（1）ST-EM 真菌相互作用在 SOM 分解和稳定中的作用是什么？ (2) 真菌类群的进化起源和功能生态是否影响它们对SOM动态的相互作用？ (3) 不同环境条件下社区中ST-EM相互作用的运作机制是什么？我们选择了四个不同的真菌类群，每个类群都由一种 EM 真菌与最相关的 ST 物种配对组成。我们设计了一个强大的模型系统来定量解决真菌相互作用对 SOM 分解和稳定的功能影响。我们的实验计划包括四个复杂程度，依次验证 ST-EM 真菌相互作用的发现：（1）生长介质上的真菌培养物，（2）微观世界，其中 EM 真菌与植物共生，（3）与森林树苗的中观世界，以及（4）树种和土壤氮可用性不同的田间地点。

项目成果

Mycorrhizal type of woody plants influences understory species richness in British broadleaved woodlands.

• DOI: 10.1111/nph.18274
• 发表时间: 2022-09
• 期刊: NEW PHYTOLOGIST
• 影响因子: 9.4
• 作者: Guy, Petra;Sibly, Richard;Smart, Simon M.;Tibbett, Mark;Pickles, Brian J.
• 通讯作者: Pickles, Brian J.

Unravelling the Facilitation-Competition Continuum Among Ectomycorrhizal and Saprotrophic Fungi

揭开外生菌根和腐生真菌之间的促进竞争连续体

• DOI: 10.2139/ssrn.4724438
• 发表时间: 2024
• 作者: Pena R