Global Diversity and Importance of Mycorrhizal and Nonmycorrhizal Plants

Abstract

The definitions of different types of mycorrhizas and problems with mycorrhizal diagnosis, especially for plants with sparse or inconsistent mycorrhizal colonisation, are discussed. These include plants which have arbuscular mycorrhizas (AM) in some habitats but have nonmycorrhizal (NM) roots in others (NM-AM plants). NM and NM-AM plants are most common in harsh environments where plant productivity is limited by soil infertility, disturbance, cold, salinity, waterlogging, etc. Revised estimates are provided for the total number of flowering plants and vascular plants with mycorrhizal or NM roots, confirming the overall importance of AM that occurs in 72% of vascular plants, while about 7% have inconsistent AM associations (NM-AM), 2% are ectomycorrhizal (EcM), <2% have ericoid mycorrhizas and 10% have orchid mycorrhizas. Estimates of the relative diversity of plants with different mycorrhiza types are provided for geographic regions along with examples where the relative dominance of mycorrhizal plants has been determined. These comparisons show that mycorrhizal plants are dominant in almost every habitat and situation, with the exception of habitats where soil conditions are hostile to fungal activity or plant productivity. Finally, the main trends in mycorrhizal evolution are briefly discussed.