Nutrient exchange within common mycorrhizal networks is altered in a multispecies environment

Abstract Although it is known that arbuscular common mycorrhizal networks (CMNs) mediate below‐ground interactions between one or two species, little is understood about their role in mediating interactions among multiple, co‐occurring plant species. We investigated the CMN‐mediated interactions among two Central European species, Inula conyzae and Crepis biennis within pots and the impact of a third plant, an invasive Echinops sphaerocephalus, on these relationships. We examined changes in C‐to‐P exchange within a CMN formed by Funneliformis mosseae sourced from Central Europe by tracking plant C cost with 13C signatures of 16:1ω5 and P acquisition to hosts with 33P only accessible to CMNs. When only native plants were present, the C cost was consistent for both species, despite CMNs favouring C. biennis with P uptake. In the presence of E. sphaerocephalus, CMNs also favoured C. biennis with P, but while C. biennis and E. sphaerocephalus provisioned similarly large portions of 13C, I. conyzae provided less. Mycorrhizal P acquisition, therefore, was the costliest for E. sphaerocephalus, which likely mitigated some I. conyzae's C cost even though both received a low proportion of 33P from CMNs. Echinops sphaerocephalus altered mineral nutrient and C exchange proportions between native plants and their CMN, suggesting that this species alters below‐ground plant interactions and that not only specific characteristic of plant host and fungal partner but also the wider plant community mediates resource exchanges between CMNs and individual plants. Read the free Plain Language Summary for this article on the Journal blog.