Mycorrhizal or not mycorrhizal? Assessing the role of root-associated fungi in plant nutrition

在自然界中，植物根系与复杂的微生物群落有关，这些微生物群落决定着植物的健康和生产力。这些群落中充满了适应扎根根部的真菌，这些真菌与植物产生了一系列致病的互惠相互作用。菌根是广泛的、稳定的根与真菌的结合体，真菌帮助植物获得营养和水分，并接受光合作用作为回报。然而，绝大多数根相关真菌对植物适应性具有未知的功能和隐式作用，这就提出了这些共生体如何进化和维持的问题。据推测，这些非菌根真菌为宿主提供了植物资源交换的利益，或者它们有助于维持根系微生物群落。事实上，最近的研究表明，非菌根真菌可以以多种方式对植物有益，包括以类似菌根的方式帮助植物吸收营养。然而，这些相互作用的普遍性仍有待检验。本项目旨在系统评估非菌根根相关真菌在协助植物营养方面的潜力。该项目将针对功能相关的根相关真菌群体，通过在营养可用性的自然梯度上进行真菌多样性采样，并通过体外富集试验来检测和分离这些真菌。选定的真菌类群在植物营养中的作用将通过植物-真菌共培养生物测定直接确定，其中营养转运将通过示踪同位素检测。系统发育和基于性状的分析将用于探索真菌谱系中功能性状的发生模式，以提出有关真菌根共生生活方式进化驱动力的假设。破译根相关真菌的隐生态将进一步加深我们对植物微生物组功能如何依赖于单个微生物和食物网的理解，并将有助于开发真菌在可持续农业中的应用方法。

In nature, plant roots associate with complex microbial communities that determine plant health and productivity. These communities are rife with fungi adapted to colonize roots, which develop a range of pathogenic to mutualistic interactions with plants. Mycorrhizas are widespread, stable root-fungus associations, in which the fungus assists the plant in acquiring nutrients and water and receives photosynthates in return. However, the large majority of root-associated fungi have unknown functions and cryptic effects on plant fitness, which raises questions about how these symbioses evolved and are maintained. It is hypothesized that these non-mycorrhizal fungi provide hosts with benefits in exchange for plant resources, or that they help to maintain root microbial communities. Indeed, recent research shows that non-mycorrhizal fungi can benefit plants in multiple ways, including the assistance in plant nutrients' uptake in a mycorrhiza-like manner. The generality of these interactions, however, remains to be tested. The project proposed here aims at a systematic assessment of the potential of non-mycorrhizal root-associated fungi in assisting plants' nutrition. The project will target functionally relevant groups of root-associated fungi by performing fungal diversity samplings across natural gradients of nutrient availability, and by using in vitro enrichment trials to detect and isolate these fungi. The involvement of selected fungal groups in plant nutrition will be directly determined by using plant-fungus co-cultivation bioassays, in which nutrient translocation will be detected by means of tracer isotopes. Phylogenetic and trait-based analyses will be used to explore patterns of functional traits occurrence across fungal lineages, in order to propose hypotheses about the forces driving the evolution of the root-symbiotic lifestyle in fungi. Deciphering the cryptic ecology of root-associated fungi will further our understanding on how plant-microbiome functions depend on individual microorganisms and food webs, and will contribute to the development of methods for the application of fungi in sustainable agriculture.