Mycorrhizal Networks

Introduction and Definition: Mycorrhizae are widespread symbiotic associations between fungi and plant roots that extend fungal access into the surrounding soil. The term mycorrhiza describes this close relationship: “A mycorrhiza is a symbiotic association between a fungus and the roots of a vascular plant.” When mycorrhizal fungal mycelium associates with the roots of multiple plants, it can form a common mycorrhizal network (CMN). Mycorrhizal associations play fundamental roles in terrestrial ecosystems by contributing to nutrient cycling, soil stability, plant growth, and ecosystem resilience. Mycorrhizal symbioses are estimated to have originated approximately 400–450 million years ago, contributing to the colonization of land by early plants. Body: Major forms of mycorrhizal associations include arbuscular, ectomycorrhizal, ericoid, and orchid mycorrhizae, which differ in their fungal partners, structures, and host ranges. In these associations, plants provide photosynthetically derived carbon to fungi, while fungi enhance plant access to water and mineral nutrients. Mycorrhizal associations influence ecosystem functioning by enhancing nutrient acquisition, supporting soil aggregation, and affecting plant community composition and soil carbon cycling. Common mycorrhizal networks have been investigated as potential pathways for the movement of resources and signals among associated plants. Experimental studies have detected movement of carbon, nitrogen, and phosphorus among plants associated with common fungal mycelia, as well as defence-associated responses in connected plants. However, the magnitude, mechanisms, and ecological consequences of these processes vary among experimental systems and remain under investigation. Knowledge of mycorrhizal symbioses is informing research in sustainable agriculture, forestry, reforestation, and ecosystem restoration. Recent scientific debate has emphasized the importance of distinguishing evidence that plants are connected, evidence that resources or signals move between them, and evidence that these processes provide ecologically meaningful benefits to recipient plants. This distinction is central to ongoing research into the ecological significance of common mycorrhizal networks.