title: Loss of functional diversity and network modularity in introduced plant-fungal symbioses.
abstract: The introduction of alien plants into a new range can result in the loss of co-evolved symbiotic organisms, such as mycorrhizal fungi, that are essential for normal plant physiological functions. Prior studies of mycorrhizal associations in alien plants have tended to focus on individual plant species on a case-by-case basis. This approach limits broad scale understanding of functional shifts and changes in interaction network structure that may occur following introduction. Here we use two extensive datasets of plant-fungal interactions derived from fungal sporocarp observations and recorded plant hosts in two island archipelago nations: New Zealand (NZ) and the United Kingdom (UK). We found that the NZ dataset shows a lower functional diversity of fungal hyphal foraging strategies in mycorrhiza of alien as compared with native trees. Across species this resulted in fungal foraging strategies associated with alien trees being much more variable in functional composition compared with native trees, which had a strikingly similar functional composition. The UK data showed no functional difference in fungal associates of alien and native plant genera. Notwithstanding this, both the NZ and UK data showed a substantial difference in interaction network structure of alien trees compared with native trees. In both cases, fungal associates of native trees showed strong modularity, while fungal associates of alien trees generally integrated into a single large module. The results suggest a lower functional diversity (in one dataset) and a simplification of network structure (in both) as a result of introduction, potentially driven by either limited symbiont co-introductions or disruption of habitat as a driver of specificity due to nursery conditions, planting, or plant edaphic-niche expansion. Recognizing these shifts in function and network structure has important implications for plant invasions and facilitation of secondary invasions via shared mutualist populations.
authors.affiliation: Bio-Protection Research Centre, Lincoln University, Box 85084, Lincoln 7647, New Zealand ian.dickie@lincoln.ac.nz.
authors.forename: Ian A
authors.initials: IA
authors.lastname: Dickie
authors.affiliation: Landcare Research, PO Box 69040, Lincoln 7640, New Zealand.
authors.forename: Jerry A
authors.initials: JA
authors.lastname: Cooper
authors.affiliation: Bio-Protection Research Centre, Lincoln University, Box 85084, Lincoln 7647, New Zealand.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Bufford
authors.affiliation: Bio-Protection Research Centre, Lincoln University, Box 85084, Lincoln 7647, New Zealand.
authors.forename: Philip E
authors.initials: PE
authors.lastname: Hulme
authors.affiliation: Bio-Protection Research Centre, Lincoln University, Box 85084, Lincoln 7647, New Zealand.|Landcare Research, PO Box 69040, Lincoln 7640, New Zealand.|Department of Plant Pathology, University of Minnesota, Saint Paul, MN 55108, United States of America.
authors.forename: Scott T
authors.initials: ST
authors.lastname: Bates
keywords: Bipartite interaction networks; ectomycorrhizal symbiosis; foraging strategies; functional traits; invasion ecology; network modularity; second-genome; soil ecology.