Mycorrhizal functions in the forest floor

菌根共生是森林生态系统植物-土壤反馈和碳循环的核心组成部分。然而，尽管已知两种主要的菌根结合力类型对凋落物分解和土壤有机质形成的影响不同，但这是否也影响了它们对森林地面（FF）作为栖息地的偏好，仍未得到解决。我们假设，在寒冷或温暖的营养贫乏的森林林分中，菌根真菌更依赖FF碳(C)，因为产生和投入真菌共生体的光合作用较少。因此，真菌群落的多样性在FF增加。在中等温度下，当菌根真菌受养分有效性的限制大于受宿主C供应的限制时，两种主要菌根结合力类型的响应导致优势分化：丛枝菌根真菌在贫磷FFs中优于丛枝菌根真菌，而在富磷FFs中优于外生菌根真菌。本研究以欧洲山毛榉（Fagus sylvatica L.， ECM寄主）与梧桐槭（Acer pseudoplatanus L.， AM寄主）混交林为样本，通过分析菌根群落组成和活性对温度升高和无机磷限制的响应，验证上述预测。为了实现我们项目的目标，我们将结合功能性状分析、同位素分离分析、13C-和15n标记实验以及胞外酶分析，对FF和矿质土壤中的菌根真菌群落进行下一代测序。该项目将完善我们对混交林FF菌根真菌生态学的认识和预测，这些混交林越来越多地暴露于升温和磷限制中。

The mycorrhizal symbiosis is a central component of plant-soil feedbacks and carbon cycles of forest ecosystems. Yet even though it is known that the two major mycorrhizal association types influence litter decomposition and soil organic matter formation differently, it remains unresolved whether this also influences their preference for the forest floor (FF) as a habitat. We hypothesize that mycorrhizal fungi are more dependent on FF carbon (C) in cold or warm nutrient-poor forest stands, since less photosynthates are produced and invested into the fungal symbiont. As a result, the diversity of the mycorrhizal fungal community in the FF increases. At intermediate temperature, when mycorrhizal fungi are stronger limited by nutrient availability than by host C supply, the response of the two major mycorrhizal association type leads to diverging superiority: Arbuscular mycorrhizal fungi are superior in P-poor FFs and ectomycorrhizal fungi in P-rich FFs. We aim to test these predictions in a transect study with mature European beech (Fagus sylvatica L., ECM host) forests admixed with sycamore maple (Acer pseudoplatanus L., AM host) by analyzing the response of the mycorrhizal community composition and activity to rising temperature and inorganic P limitation. To achieve the objectives of our project, we will combine functional trait analyses, isotopic fractionation analysis, a 13C- and 15N-labeling experiment, and extracellular enzyme analyses with next generation sequencing of the mycorrhizal fungal community in the FF and mineral soil. This project will refine our understanding and prediction of the ecology of mycorrhizal fungi in the FF of mixed beech forests, which are increasingly exposed to rising temperature and P limitation.