A unique mode of parasitism in the conifer coral treeParasitaxus ustus(Podocarpaceae)
2005
Feild, TS | Brodribb, TJ
Almost all parasitic plants, including more than 3000 species,are angiosperms. The only suggested gymnospermexception is the New Caledonian conifer,Parasitaxusustus, which forms a bizarre graft-like attachment to theroots of another coniferFalcatifolium taxoides. Yet, thedegree of resource dependence ofParasitaxusonFalcatifoliumhas remained speculative. Here we show thatParasitaxusis definitively parasitic, but it displays a physiologicalhabit unlike any known angiosperm parasite.Despite possessing chloroplasts, it was found that theburgundy red shoots ofParasitaxuslack significant photosyntheticelectron transport. However unlike nonphotosyntheticangiosperm parasites (holoparasites),tissues ofParasitaxusare considerably enriched in13carbonrelative to its host. In line with anatomical observations offungal hyphae embedded in the parasite/host union, stablecarbon isotopic measurements indicate that carbon transportfrom the host toParasitaxusmost likely involves afungal partner. Therefore,Parasitaxusparallels fungusfeedingangiosperms (mycoheterotrophs) that steal carbonfrom soil mycorrhizal fungi. Yet with its tree-like habit,association with fungi residing within the host union, highstomatal conductance, and low water potential, it is demonstratedthatParasitaxusfunctions unlike any knownangiosperm mycoheterotroph or holoparasite.Parasitaxusappears to present a unique physiological chimera of mistletoe-like water relations and fungal-mediated carbon traffickingfrom the host.
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