How do ecological trade-offs drive ectomycorrhizal fungal community assembly? Fine-scale processes with large-scale implications

几乎所有的植物都与栖息在根部的共生真菌有关。这些菌根真菌为植物提供营养来源，作为交换，植物为真菌伴侣提供碳来源。树木通常与外生菌根真菌（ECM）相关，这些真菌对生态系统中的许多过程至关重要，包括分解和氮和碳循环。不同种类的ECM真菌在获取营养物质的能力或它们执行的一整套功能上可能有所不同。因此，了解影响ECM真菌物种组成的因素对于更好地全面了解土壤养分循环、森林健康、生产力和生物多样性非常重要。ECM真菌的个别物种在树木的根部竞争空间。有些真菌可能比其他真菌更适合争夺根空间，但最好的竞争者在其他重要策略上的表现可能不太好，比如养分获取。这些“权衡”，即在一个方面表现最佳的能力与另一个方面表现下降相关，已知是如此多的大型生物物种可以在一个栖息地中共存的根本原因。然而，这些权衡在影响菌根群落中的作用知之甚少，尽管它在确定这些生态重要真菌的物种组成方面可能很重要。在这项研究中，我检验了这样一个假设，即营养获取（可以吸收的氮的宽度）和竞争力（在植物根系上赢得空间和获得植物碳的能力）之间的权衡是驱动菌根真菌物种的关键过程，这些真菌物种可以在单个植物根系上共同发生，这最终影响了整个景观尺度上观察到的真菌群落组成。我在实验室里用一系列的实验来验证这个假设，这些实验让我可以追踪从植物提供给单个真菌物种的碳的数量，以及作为交换，有多少氮从真菌传递给植物。在一个已经接受了30多年试验氮肥的森林中进行的实地实验将使我能够测试这些权衡在更复杂的自然环境中是如何运作的，在那里氮的可用性可能会改变权衡的动态以及植物和真菌伴侣之间碳和氮的交换速率。最后，我将使用一系列长期监测的森林地块，测试在实验室和野外观察到的结果如何扩大到整个欧洲ECM物种发生的模式。英国的森林提供了重要的舒适性，碳捕获和木材价值，而全球树木形成了超多样化的热带雨林，并在北方生态系统中储存了大量的碳。由于ECM真菌是所有树木主导的生态系统的重要组成部分，该项目的产出将为我们自然环境的这一关键方面提供高质量的见解，并有助于在英国及其他地区发展未来的研究、政策和林业实践。

Nearly all plants are associated with mutualistic fungi which inhabit their roots. These mycorrhizal fungi provide the plants with a source of nutrients and in exchange, the plant provides the fungal partner with a source of carbon. Trees typically associate with ectomycorrhizal (ECM) fungi, which are critical to many processes within ecosystems including decomposition and nitrogen and carbon cycling. Different species of ECM fungi can differ in their ability to acquire nutrients or in the suite of functions that they carry out. Understanding what affects the species composition of ECM fungi is therefore important for a better overall understanding of nutrient cycling in soils, forest health, productivity and biodiversity. Individual species of ECM fungi compete for space on the roots of trees. Some fungi are likely to be better competitors for root space than others, but the best competitors are likely to perform less well in other important strategies, such as nutrient acquisition. These 'trade-offs', which mean the ability to perform optimally in one respect is associated with a decline in performance in another, are known to be a fundamental reason why so many species of macro-organisms can co-occur in a single habitat. However, the role that these trade-offs play in affecting mycorrhizal communities is poorly understood despite its probable importance in determining the species composition of these ecologically vital fungi.In this fellowship, I test the hypothesis that trade-offs between nutrient acquisition (the breadth of nitrogen that can be taken up) and competitiveness (the ability to win space on plant roots and obtain plant carbon) is a critical process driving the species of mycorrhizal fungi that can co-occur on individual plant roots, and that this ultimately affects the community composition of fungi observed across landscape-scales. I test this hypothesis using a series of experiments in the laboratory which allow me to trace the quantities of carbon being supplied from the plant to individual species of fungi, and in exchange how much nitrogen is being passed from the fungus to the plant. Field experiments in a forest which has received more than 30 years of experimental nitrogen fertilisation will allow me to test how these trade-offs operate in a more complex natural setting, where the availability of nitrogen may alter the dynamics of the trade-off and the exchange rate of carbon and nitrogen between plant and fungal partner. Finally, I will test how the results observed in the lab and field scale-up to patterns of ECM species occurrence across Europe, using a series of long-term monitoring forest plots.The UK's forests provide significant amenity, carbon-capture and timber value, whilst globally trees form hyper-diverse tropical rainforests, and hold significant stores of carbon in boreal ecosystems. As ECM fungi are a critical component of all tree-dominated ecosystems, the outputs from this project will provide high-quality insights into this key aspect of our natural environment, and help to develop future research, policy and forestry practice in the UK and beyond.