Ectomycorrhiza functioning in young and mature forest stands

多达15,000种真菌与木本植物的根形成了称为外生菌根的共生组织。有如此多的外生菌根真菌的原因之一可能是因为它们填充了土壤中的特定生态位。分子生物学的新方法证明，不同外生菌根真菌的菌丝确实存在于不同的土层或微区。此外，菌丝(延伸到根部之外的菌丝)可能位于土壤剖面的不同部分，而不是被该真菌定植的根。然而，我们几乎不知道这些真菌的生理学如何与微区的分布有关。我的研究小组使用几种方法来研究外生菌根真菌在田间养分吸收和养分循环中的作用。重要的是，在可能的情况下，在现场研究外生菌根，以便与菌丝相关的细菌是本地细菌，并且由这些联合形成的广泛的菌丝网络可以保持完好。我们将使用一种基于根窗口的印迹技术来识别毫米级的胞外酶活性的“热点”。这些酶参与了有机物的分解。以印记为指导，我们将收集非常小的土壤样本，从中我们将扩增真菌DNA。然后，我们将确定热点地区的真菌群落是否与酶活性较低的微型地点的真菌群落不同。在一些地点，我们将测试腐烂木材中更常见的外生菌根真菌是否更有可能分泌酶来分解木材中发现的木质素和纤维素。我们将通过直接测量这些酶的活性以及检测土壤中这些酶的mRNA来做到这一点。我们还将使用稳定的氮同位素作为示踪剂，以确定在砍伐群落中占主导地位的真菌从森林中发现的真菌吸收有机氮的能力是否不同。土壤微生物群落的大部分变化“仍然被视为随机噪声”。我们的研究将有助于确定外生菌根真菌之间的生理差异是否是影响其分布的因素之一。

As many as 15,000 species of fungi form symbiotic associations called ectomycorrhizas with roots of woody plants. One reason that there are so many ectomycorrhizal fungi may be because they fill specific niches in the soil. New methods in molecular biology have demonstrated that the hyphae of different ectomycorrhizal fungi are indeed found in different soil horizons or microsites. In addition, the extramatrical hyphae (those that extend well beyond the root) may be located in a different part of the soil profile from roots colonized by that fungus. However we know almost nothing about how the physiologies of these fungi relate to distribution amongst microsites. My research group uses several approaches to study the role of ectomycorrhizal fungi in nutrient uptake and nutrient cycling in the field. It is important to study ectomycorrhizal physiology in situ, where possible, so that bacteria associated with hyphae are native ones, and so that the extensive network of hyphae formed by these associations can remain intact. We will use a root window-based imprinting technique to identify mm-scale 'hot spots' of extracellular enzyme activity. These enzymes are involved in organic matter breakdown. Using the imprints as a guide, we will collect very small soil samples, from which we will amplify fungal DNA. We will then determine whether fungal communities in the hot spots differed from those in microsites with low enzyme activities. At some sites, we will test whether ectomycorrhizal fungi that are more common in decayed wood are more likely to secrete enzymes that break down lignin and cellulose found in wood. We will do this both by measuring the activities directly, as well as by detecting soil mRNA for these enzymes. We will also use stable isotopes of nitrogen as tracers to determine whether fungi that dominate clearcut communities differ in their ability to absorb organic N from fungi found in forests with well-developed forest floors. Much of the variation in soil microbial communities is "still viewed as random noise". Our research will help to determine whether physiological differences amongst ectomycorrhizal fungi is one of the factors that influences their distribution.