Switching belowground partners: biogeochemical consequences of mycorrhizal type in aspen forests

微生物对人类的健康、食物和与其相互作用的生态系统至关重要。在生活在土壤中的微生物中，真菌是养分和碳循环的关键角色。真菌分解有机物，并通过菌根（根与菌根真菌之间的共生关系）影响植物的营养和生长。提出的研究解决了土壤真菌如何介导与当前广泛的树种范围转移相关的土壤变化。这项研究很重要，因为它将评估树木和真菌之间的相互作用如何控制陆地系统中的碳循环，这是在评估气候变化影响时经常被忽视的一个关键环节。***在加拿大西部，已经预测到森林组成的变化，并且在北方森林的南部边界已经观察到这种变化是强烈的。颤栗杨树是这一地区广泛分布的树木，向北延伸到北方森林，向南延伸到草原。杨树也是世界上为数不多的与丛枝菌根真菌和外生菌根真菌（菌根的两大类群）共生的树种之一。所有的菌根真菌都依赖于活的宿主来获取碳，但丛枝菌根真菌和外生菌根真菌在生理、碳需求以及排泄到土壤中的酶的程度和类型上都有所不同。因此，森林中外生菌根对丛枝菌根的优势可能对土壤有明显的影响。特别是，预测土壤碳通量至关重要，因为即使通量的微小变化也会对碳循环产生重大影响，因为土壤碳库非常大。关于控制哪种菌根类型在双定殖宿主上占优势的生态因素知之甚少。在接下来的五年里，我的研究计划将确定在范围紧张地区的白杨林中发生的外生菌根和丛枝菌根之间转变的原因和后果。这项研究的预期意义有三个方面。从历史上看，这些真菌群一直是单独研究的。拟议的研究将它们的相互作用视为对森林动态的响应，这是一个迄今为止被忽视的创新观点。2)丛枝菌根和外生菌根优势的变化已经在不同的景观中被追踪到，但不是在一个单一的、广泛分布的物种中。本研究中描述的新方法测试了通过单一树种表达气候变化是否可以改变土壤真菌，从而改变土壤中的养分和碳循环。3)提出的研究建立在关于菌根如何介导土壤和植物之间碳通量的新兴观点的基础上。这一观点是认识到菌根在森林中除了植物营养之外的复杂作用的转折点。

Microbes are paramount in the health of humans, their food and the ecosystems with which they interact. Of the microbes that live in soil, fungi are key players in cycling of nutrients and carbon. Fungi decompose organic matter, and through mycorrhizas, a symbiosis between roots and mycorrhizal fungi, they affect the nutrition and growth of plants. The proposed research addresses how soil fungi may mediate changes to soils associated with current range shifts of a widespread tree species. This research is important because it will evaluate how carbon cycling in terrestrial systems is controlled by interactions between trees and fungi, a critical link often overlooked when assessing the impacts of climate change. *** In western Canada, shifts in forest composition have been predicted and already observed to be intense at the southern limits of boreal forests. Trembling aspen is a widespread tree in this region of range tension, extending north into the boreal forest and south into grasslands. Aspen is also one of the few tree species worldwide that forms symbioses with arbuscular and ectomycorrhizal fungi, the two major groups of mycorrhizas. All mycorrhizal fungi rely on living hosts for carbon, but arbuscular mycorrhizal fungi and ectomycorrhizal fungi differ in their physiology, carbon demands and the extent and types of enzymes excreted into soils. In consequence, the dominance of ectomycorrhizas versus arbuscular mycorrhizas in forests may have pronounced effects on soils. In particular, predicting soil carbon fluxes is imperative as even small changes in fluxes can have substantial impacts on carbon cycling because the soil carbon pool is so large. Little is known on the ecological factors controlling which mycorrhizal type dominates on dually colonized hosts. Over the next five years, my research program will identify causes and consequences of shifts between ectomycorrhizas and arbuscular mycorrhizas in aspen forests occurring in regions of range tension.*** The anticipated significance of this research is threefold. 1) Historically, these groups of fungi have been studied in isolation. The proposed research considers their interaction as a response to forest dynamics, an innovative perspective ignored to date. 2) Shifts in arbuscular and ectomycorrhizal dominance have been tracked across landscapes, but not within a single, widespread species. Novel approaches described in this proposed research test whether the expression of a changing climate through a single tree species can alter soil fungi to the extent they change nutrient and carbon cycling in soils. 3) The proposed research builds on emerging perspectives on how mycorrhizas mediate carbon fluxes between soils and plants. This perspective is a turning point in recognizing the complex role mycorrhizas play in forests aside from plant nutrition.