Mycorrhizal associations between fungi and plant roots have globally significant impacts on nutrient cycling. Mucoromycotina ‘fine root endophytes’ (MFRE) are a distinct and recently characterised group of mycorrhiza‐forming fungi that associate with the roots of a range of host plant species. Given their previous misidentification and assignment as arbuscular mycorrhizal fungi (AMF) of the Glomeromycotina, it is now important to untangle the specific form and function of MFRE symbioses. In particular, relatively little is known about the nature of MFRE colonisation and its role in N uptake and transfer to host plants. Even less is known about the mechanisms by which MFRE access and assimilate N, and how this N is processed and subsequently exchanged with host plants for photosynthates. Here, we summarise and contrast the structures formed by MFRE and arbuscular mycorrhizal fungi in host plants as well as compare the N source preference of each mycorrhizal fungal group with what is currently known for MFRE N uptake. We compare the mechanisms of N assimilation and transfer to host plants utilised by the main groups of mycorrhizal fungi and hypothesise potential mechanisms for MFRE N assimilation and transfer, outlining directions for future research.

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The intensification of agriculture over the past decades has helped increase crop yields but has also led to various environmental issues, potentially undermining future productivity. One of the options considered for increasing the sustainability of agriculture is the stimulation or enhancement of microorganisms that associate with plants and help them acquire more nutrients from the soil leading to benefits such as increased growth. One key player considered are arbuscular mycorrhizal fungi (AMF), a group of below-ground fungi that form symbiotic relationships with the vast majority of land plants. However, evidence from lab and field trials suggests that not all plants respond equally to colonization by these fungi, and research is on-going to better understand the context-dependency of the symbiosis. Moreover, introducing AMF to agricultural fields through the application of commercial inoculants that contain fungal spores and hyphae has been inconsistent in their desired effects of boosting crop yield and quality. Recently, a quality framework has been put forward to try and increase the reliability of these inocula so farmers can make better use of them. Although further research on the fundamental and applied aspects of plant–arbuscular mycorrhizal associations is required, agricultural practices that favour these fungi should be encouraged as they are likely to lead to wider benefits and ultimately contribute to a more sustainable agricultural system.