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Abstract Arbuscular mycorrhizal (AM) fungi can support the establishment of mycotrophic plants in new environments. However, the role of mycorrhizal symbiosis in interactions between perennial and weedy annual plants is not well understood. In our current study, we examine how widespread generalist AM fungi and soil disturbance, including disturbance of AM fungal networks (CMNs), affect the performance of two late-successional perennial plants of Central Europe, Senecio jacobaea and Crepis biennis, co-occurring with weedy annual forbs, Conyza canadensis and Erigeron annuus . Although presence of weedy annual E. annuus or C. canadensis did not affect the performance of the paired perennials, AM fungi supported perennial C. biennis in competition with weedy annual E. annuus . However, this AM-aided underpinning was independent of disturbance of CMNs. Conversely, although AM fungi benefited perennial S. jacobaea , this did not affect its competitive abilities when grown with weedy annual C. canadensis . Similarly, soil disturbance, independent of AM fungal presence, improved plant tissue P and biomass production of S. jacobaea , but not its competitive abilities. Our results show AM fungi may be advantageous for perennial plants growing in competition with weedy annual plants. Therefore, maintaining healthy soils containing an abundance of AM fungi, may encourage late successional perennial plants, potentially limiting establishment of weedy annual plant species. 

Abstract In a globalized world, plant invasions are common challenges for native ecosystems. Although a considerable number of invasive plants form arbuscular mycorrhizae, interactions between arbuscular mycorrhizal (AM) fungi and invasive and native plants are not well understood. In this study, we conducted a greenhouse experiment examining how AM fungi affect interactions of co-occurring plant species in the family Asteracea, invasive Echinops sphaerocephalus and native forb of central Europe Inula conyzae . The effects of initial soil disturbance, including the effect of intact or disturbed arbuscular mycorrhizal networks (CMNs), were examined. AM fungi supported the success of invasive E. sphaerocephalus in competition with native I. conyzae , regardless of the initial disturbance of CMNs. The presence of invasive E. sphaerocephalus decreased mycorrhizal colonization in I. conyzae , with a concomitant loss in mycorrhizal benefits. Our results confirm AM fungi represent one important mechanism of plant invasion for E. sphaerocephalus in semi-natural European grasslands.