The role of soil fertility in the function of mycorrhizal associations

背景-丛枝菌根(AM)真菌和外生菌根(ECM)真菌在植物养分获取中起着关键作用，但它们对土壤有机碳(SOC)的稳定作用可能存在很大差异。ECM真菌被认为可以促进SOC的稳定和储存，而有证据表明AM真菌可以促进SOC的矿化和以CO2的形式释放。菌根真菌储存碳的倾向可能受到土壤肥力的影响。植物-菌根互惠关系的基础是植物向真菌网络提供碳，以换取增强的养分吸收。有强有力的证据表明，菌根的作用是有限的，最近的研究表明，营养的有效性可以改变植物和AM真菌之间的关系，从互惠关系变为半寄生关系。该项目的目的是：1)首次直接比较AM和ECM真菌对土壤碳储存和释放的贡献；2)评估养分有效性在构建植物与菌根真菌之间的资源交换中的作用。研究计划-该项目将使用与AM和ECM真菌(包括杨树和杨树)相关的树苗进行一系列温室实验。同一土壤类型和两种树种之一的盆栽将接种AM、ECM、两种真菌或两种真菌的灭菌组合。不同养分的有效性将通过添加适当的化肥进行实验控制，土壤碳的储存或释放将通过定期测量土壤二氧化碳(土壤呼吸)和13C脉冲标记来评估，以跟踪碳通过植物和菌根真菌流入土壤的情况。菌根功能的变化将通过测量树木生长、叶片营养、菌根侵染率和菌根群落组成来确定。选定的处理将被用于真菌表型和功能基因的分子表征。这些实验的结果将被用于通知和发展其他树种的额外实验和/或自然肥力梯度的实地调查，以测试研究的更广泛的适用性。

Background - Arbuscular mycorrhizal (AM) fungi and ectomycorrhizal (ECM) fungi play key roles in plant nutrient acquisition but their contributions to the stabilization of soil organic carbon (SOC) could differ substantially. ECM fungi are thought to promote the stabilization and storage of SOC, whereas there is evidence that AM fungi can stimulate the mineralization of SOC and its release as CO2. The propensity of mycorrhizal fungi to store carbon is likely to be influenced by soil fertility. The plant-mycorrhizal mutualism is based on the provision of carbon by plants to the fungal network in return for enhanced nutrient uptake. There is strong evidence that mycorrhizal function is nutrient-limited and recent research suggests that nutrient availability can alter the relationship between plants and AM fungi from mutualistic to semi-parasitic. This project aims to: 1) Perform the first direct comparison of AM and ECM fungal contributions to soil carbon storage and release; and 2) Evaluate the role of nutrient availability in structuring the exchange of resources between plants and mycorrhizal fungi. Programme of research - The project will involve a series of greenhouse experiments using tree seedlings that associate with both AM and ECM fungi (including aspen and poplar). Pots with a common soil type and one of the two tree species will be inoculated with AM, ECM, both fungi, or a sterilized combination of both fungi. The availability of different nutrients will be manipulated experimentally by adding appropriate fertilisers.The storage or release of soil carbon will be assessed by regular measurements of soil CO2 (soil respiration) and 13C pulse-labelling to track the flow of carbon through plants and mycorrhizal fungi into the soil. Changes in mycorrhizal function will be determined from measurements of tree growth, foliar nutrients, mycorrhizal infection rates, and mycorrhizal community composition. Selected treatments will be chosen for molecular characterisation of fungal phenotypes and functional genes.The results of these experiments will be used to inform and develop additional experiments with other tree species and/or field surveys along natural fertility gradients to test the wider applicability of the research.