Network perspectives of ectomycorrhizal associations

Network analysis has successfully been applied to investigate ecological interactions. Most information about the structure of ecological networks is derived from aboveground interactions of plants with pollinators and seed dispersers. Here we examine ectomycorrhizal interactions between plants and fungi in a network perspective that has received little attention so far. For network analyses, we examined the main network propertiesnestedness and modularity. Certain ectomycorrhizal fungal communities displayed modularity, which is directly attributable to partner selectivity and, thus, context dependent. Our data also showed that ectomycorrhizal networks exhibit non-nested or anti-nested patterns, which is in contrast to other mutualistic interactions. The low level of nestedness may indicate that specific ectomycorrhizal plant species do not favour generalist ectomycorrhizal fungi over specialists and vice versa. This can stem from a strong selection pressure of host in choosing its mycobionts as suggested from the substantial host phylogeny effect on ectomycorrhizal fungal richness and community. Whether the low level of nestedness in ectomycorrhizal associations is due to methodological or ecological factors requires further investigation.