Analytical methods can offer insights into the structure of biological networks, but mechanisms that determine the structure of these networks remain unclear. We conducted a synthesis based on 111 previously published datasets to assess a range of ecological and evolutionary mechanisms that may influence the plant-associated fungal interaction networks. We calculated the relative host effect on fungal community composition and compared nestedness and modularity among different mycorrhizal types and endophytic fungal guilds. We also assessed how plant-fungal network structure was related to host phylogeny, environmental and sampling properties. Orchid mycorrhizal fungal communities responded most strongly to host identity, but the effect of host was similar among all other fungal guilds. Community nestedness, which did not differ among fungal guilds, declined significantly with increasing mean annual precipitation on a global scale. Orchid and ericoid mycorrhizal fungal communities were more modular than ectomycorrhizal and root endophytic communities, with arbuscular mycorrhizal fungi in an intermediate position. Network properties among a broad suite of plant-associated fungi were largely comparable and generally unrelated to phylogenetic distance among hosts. Instead, network metrics were predominantly affected by sampling and matrix properties, indicating the importance of study design in properly inferring ecological patterns.

Department of Biology Plant Conservation and Population Biology KU Leuven Kasteelpark Arenberg 31 B 3001 Heverlee Belgium

Department of Botany University of Tartu 40 Lai Street 51005 Tartu Estonia

Department of Botany University of Tartu 40 Lai Street 51005 Tartu Estonia Department of Organismal Biology Evolutionary Biology Centre Uppsala University Norbyvägen 18D 75236 Uppsala Sweden

Department of Botany University of Tartu 40 Lai Street 51005 Tartu Estonia Institute of Botany Academy of Sciences of the Czech Republic CZ 252 43 Průhonice Czech Republic Faculty of Science Charles University CZ 128 44 Prague 2 Czech Republic

Department of Plant Biology University of Minnesota 1445 Gortner Ave St Paul MN 55108 USA

Natural History Museum University of Tartu 14a Ravila 50411 Tartu Estonia

Natural History Museum University of Tartu 14a Ravila 50411 Tartu Estonia Department of Botany University of Tartu 40 Lai Street 51005 Tartu Estonia

Shenzhen Key Laboratory for Orchid Conservation and Utilization The National Orchid Conservation Center of China and The Orchid Conservation and Research Center of Shenzhen 518114 Shenzhen China Center for Biotechnology and BioMedicine and Division of Life and Health Sciences Graduate School at Shenzhen Tsinghua University 518055 Shenzhen China State Key Laboratory of Mycology Institute of Microbiology Chinese Academy of Sciences Beijing 100101 China

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