Mycorrhizal associations and other means of nutrition of vascular plants: understanding the global diversity of host plants by resolving conflicting information and developing reliable means of diagnosis

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    Abstract

    A comprehensive appraisal of the mycorrhizalliterature provides data for 336 plant familiesrepresenting 99% of flowering plants, with regard tomycorrhizas and other nutritional adaptations. In total,arbuscular (AM), orchid, ectomycorrhizas (EM) andericoid mycorrhizas and nonmycorrhizal (NM) rootsoccur in 74%, 9%, 2%, 1% and 6% of Angiospermspecies respectively. Many families of NM plantshave alternative nutritional strategies such as parasitism,carnivory, or cluster roots. The remainingangiosperms (8%) belong to families reported to haveboth AM and NM species. These are designated asNM-AM families here and tend to occur in habitatsconsidered non-conducive to mycorrhizal fungi, suchas epiphytic, aquatic, extremely cold, dry, disturbed,or saline habitats. Estimated numbers of species ineach category of mycorrhizas is presented with lists ofNM and EM families. Evolutionary trends are alsosummarised by providing data on all clades andorders of flowering and non-flowering vascular plantson a global scale. A case study of Western Australianplants revealed that plants with specialised nutritionalmodes such as carnivory, cluster roots, or EM weremuch more diverse in this ancient landscape withinfertile soils than elsewhere. Detailed information onthe mycorrhizal diversity of plants presented here islinked to a website (mycorrhizas.info) to allow data toremain current. Over a century of research effort hasresulted in data on mycorrhizal associations of >10,000plant species that are of great value, but also somewhatof a liability due to conflicting information about somefamilies and genera. It is likely that these conflicts resultin part from misdiagnosis of mycorrhizal associationsresulting from a lack of standardisation in criteria usedto define them. Families that contain both NM and AMspecies provide a second major source of inconsistency,but even when these are excluded there is a ∼10%apparent error rate in published lists of mycorrhizalplants. Arbuscules are linked to AM misdiagnosis sincethey are used less often than vesicles to recognise AMassociations in roots and apparently occur sporadicallyin NM plants. Key issues with the diagnosis ofmycorrhizal plants are discussed using the Cyperaceaeas a case study. Detailed protocols designed to consistentlydistinguish AMfrom endophytic GlomeromycotanFungus Colonisation (GFC) are provided. This reviewaims to stimulate debate and provide advice to researchersdelving into root biology.
    Original languageEnglish
    Pages (from-to)37-77
    JournalPlant and Soil
    Volume320
    Issue number1/2
    DOIs
    Publication statusPublished - 2009

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