DIFFERENTIAL PRODUCTION OF OXALATE BY MYCORRHIZAL FUNGI IN ARID ECOSYSTEMS

Oxalate crystals and elements binding to the surfaces of mycorrhizal f ungal hyphae were examined using scanning electron microscopy coupled with X-ray analysis of elemental composition. Mycorrhizae from the ari d zone vegetation types in southern California were examined including chaparral, riparian oak woodlands, coastal sage, grasslands, and dese rts. Only mat-forming ectomycorrhizal hyphae, such as Hysterangium sep arabile, were found to produce oxalate crystals. None of the arbuscula r mycorrhizal fungal hyphae (Glomus spp. and Acaulospora elegans) exam ined had crystal structures associated with them. The hyphae of Hyster angium separabile without crystals did not show the Ca peaks that were present when the crystals existed nor did the arbuscular mycorrhizal fungal hyphae have the Ca peaks. The elimination of arbuscular mycorrh izae using benomyl did not affect soil P or oxalate. These data indica te that there are some fundamental differences in chemical exudation b etween mycorrhizal fungi that could affect P uptake and cycling in ari d ecosystems.