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

微生物对人类的健康、食物和与之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--根部和菌根真菌之间的共生--影响植物的营养和生长。这项拟议的研究解决了土壤真菌可能如何调节与广泛分布的树种的当前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的碳循环，而树木和真菌之间的相互作用是评估气候变化影响时经常被忽视的关键环节。 在加拿大西部，森林组成的变化已经被预测并已经在北方森林的南部边界被观察到是剧烈的。颤杨是这片山脉紧张地区的一种广泛分布的树木，向北延伸到北方的森林，向南延伸到草原。白杨也是世界上少数几个与丛枝菌根真菌和外生菌根真菌形成共生的树种之一，丛枝菌根真菌和外生菌根真菌是菌根的两大类群。所有的菌根真菌都依赖于活的宿主来获得碳，但丛枝菌根真菌和外生菌根真菌在生理、碳需求以及分泌到土壤中的酶的程度和类型上有所不同。因此，森林中外生菌根对丛枝菌根的优势可能会对土壤产生显著的影响。特别是，预测土壤碳通量是当务之急，因为由于土壤碳库如此之大，即使是通量的微小变化也可能对碳循环产生重大影响。关于控制菌根类型在双重定殖寄主上占优势的生态因素，人们知之甚少。在接下来的五年里，我的研究计划将确定在范围紧张的地区发生的白杨林中外生菌根和丛枝菌根之间转移的原因和后果。 本研究的预期意义有三个方面。1)从历史上看，这些真菌类群都是孤立研究的。拟议的研究将它们的相互作用视为对森林动态的回应，这是迄今为止被忽视的一个创新观点。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、广泛分布的物种内。这项拟议的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会改变土壤真菌，从而改变土壤中的养分和碳循环。3)拟议的研究建立在关于菌根如何调节土壤和植物之间的碳通量的新兴观点的基础上。这一观点是认识到除了植物营养之外，菌根在森林中发挥的复杂作用的一个转折点。

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.