Mycelium biomass and community composition impact nutrient concentration in arbuscular mycorrhizal fungi at fine spatial scale

Abstract The dynamic exchange of carbon (C) and nutrients between arbuscular mycorrhizal (AM) fungi and their host plants is crucial for shaping the spatial heterogeneity of nutrients within the hyphal network. This exchange is influenced not only by mycelial growth and its interactions with plants but also by the variability of soil nutrients. Despite its importance, the spatial heterogeneity of nutrients within the mycelial network and the factors driving this variability remain poorly understood. In the field of plant–AM fungi interactions, many studies have predominantly concentrated on large‐scale spatial patterns, disregarding the heterogeneity at fine scales and potentially missing vital insights into nutrient exchange between plants and AM fungi. We conducted an experiment to quantify the spatial heterogeneity of plant–soil–mycelia nutrients within a gridded 2 × 2 m 2 quadrat. Hyphal in‐growth bags were installed to extract pure AM mycelium. The concentrations of C ([C]), nitrogen ([N]), and phosphorus ([P]) in both plant and mycelium tissues were measured. Additionally, the AM fungal community from the extracted hyphae was sequenced to assess AM fungal composition. Mycelium [N] and [P] at fine scales ranged from 2.18% to 3.37% and 0.99% to 4.46%, respectively, and their variations were much higher than those in shoot and root tissues. Mycelium stored significant amounts of nutrients, particularly [P] (2.27% in average), with levels exceeding those found in plant tissue by over 20‐fold. Mycelium [C] or [N] concentration was negatively correlated, while mycelium [P] was positively correlated with mycelium biomass. This suggests that the primary driving factor behind the variability in mycelium nutrients is mycelium biomass, which is somewhat influenced by AM fungal species composition. Investigating the variability of mycelium nutrients at fine scales enhances our understanding of nutrient cycling within ecosystems. This research also highlights the importance of studying the functional traits of AM fungi and introduces the concept that mycelium could serve as underground P reservoirs. Read the free Plain Language Summary for this article on the Journal blog.