Decomposition of ectomycorrhizal fine roots

树木将很大一部分生产力分配给它们细小的营养根部。在北部的森林中，这些根中的大多数被外生菌根真菌定居--这种真菌共生体有助于吸收养分和水分，以换取植物糖。虽然外生菌根细根的周转代表着碳和氮对土壤生态系统的巨大输入，但我们对涉及的分解者以及所释放的资源的命运知之甚少。外生菌根细根大约40%是真菌组织，含有甲壳素，因此比植物组织含有更多的氮。然而，目前还不清楚哪些生物主导了森林土壤中真菌的分解。细菌和真菌的分解影响土壤养分的有效性和碳固存，因为资源在细菌群落中的移动比通过真菌群落的移动更快。在碱性土壤中，细菌被认为是甲壳素的主要分解者，在酸性条件下，土壤真菌被认为是更重要的。然而，真菌的细菌分解可能会随着温度的升高而增加，因此在气候变暖的情况下，更大比例的真菌碳和氮可能会通过更不稳定的细菌群落。细根也由真菌内生菌在内部定植。尽管人们对这些真菌的生态作用知之甚少，但它们可能参与了外生菌根植物成分的分解，并且很好地定位在根组织中。形成特定外生菌根的共生真菌也可能影响其分解速度，因为一些物种产生抗菌化合物。*本研究的目标是：1)利用基于DNA的技术确定哪些分解者在不同的环境条件下利用外生菌根中的真菌成分；2)利用RNA技术(基因表达)跟踪整个外生菌根分解过程中的微生物活动；3)确定不同真菌种类形成的外生菌根的分解速率，以表征顽固性物种产生的抗微生物化合物。*加拿大景观的一个显著特征是北方森林，这是一个生态系统，在这个生态系统中，所有优势树种都形成了外生菌根。了解细菌、土壤真菌、根内生真菌和外生菌根真菌在细根分解过程中的相对重要性，是解决由此产生的资源流经我们北方森林的途径的关键。关于土壤微生物在不同环境条件下的动态作用的信息，包括气候变化下的预期作用，对于理解现在和未来北方森林生态系统的功能也是至关重要的。********

Trees allocate a large portion of their productivity to their fine feeder roots. In northern forests, the majority of these roots are colonized by ectomycorrhizal fungi - fungal symbionts that aid in nutrient and water uptake in exchange for plant sugars. Although the turnover of ectomycorrhizal fine roots represents an enormous input of carbon and nitrogen into the soil ecosystem, we have very little information regarding the decomposers involved, and therefore the fate of the resources liberated. Ectomycorrhizal fine roots are approximately 40% fungal tissue, which contains chitin and therefore significantly more nitrogen than plant tissue. However, it is not clear which organisms dominate the breakdown of fungi in forest soils. Bacterial vs fungal decomposition impacts both soil nutrient availability and carbon sequestration, as resources move more quickly through bacterial communities than through fungal communities. Bacteria are thought to be the dominant decomposers of chitin in alkaline soils, and soil fungi are considered to be more important under acidic conditions. However, bacterial decomposition of fungi may increase with higher temperatures, such that a larger proportion of fungal carbon and nitrogen may move through the more labile bacterial community in a warmer climate. Fine roots are also colonized internally by fungal endophytes. Although the ecological roles of these fungi are poorly understood, they may be involved in the decomposition of the plant component of ectomycorrhizae, and are well positioned within the root tissue. The symbiotic fungus forming a given ectomycorrhiza may also influence its decomposition rate, as some species produce antimicrobial compounds. ***The objectives of the proposed research are to: 1) determine which decomposers utilize the fungal component of ectomycorrhizae under different environmental conditions using DNA based techniques, 2) track microbial activity during the decomposition of whole ectomycorrhizae using RNA techniques (gene expression) and 3) determine the decomposition rates of ectomycorrhizae formed by different fungal species, characterizing the antimicrobial compounds produced by recalcitrant species. ***A prominent feature of the Canadian landscape is the boreal forest, an ecosystem in which all dominant tree species form ectomycorrhizae. Knowing the relative importance of bacteria, soil fungi, root endophytes and ectomycorrhizal fungi in the process of fine root decomposition is key to resolving the pathways though which the resulting fluxes of resources move through our northern forests. Information on the dynamic roles of soil microbes under varying environmental conditions, including those expected under climate change, is also critical to understanding present and future boreal forest ecosystem function. ********