Differential production of oxalate by mycorrhizal fungi in arid ecosystems

Oxalate crystals and elements binding to the surfaces of mycorrhizal fungal hyphae were examined using scanning electron microscopy coupled with X-ray analysis of elemental composition. Mycorrhizae from the arid zone vegetation types in southern California were examined including chaparral, riparian oak woodlands, coastal sage, grasslands, and deserts. Only mat-forming ectomycorrhizal hyphae, such as Hysterangium separabile, were found to produce oxalate crystals. None of the arbuscular mycorrhizal fungal hyphae (Glomus spp. and Acaulospora elegans) examined had crystal structures associated with them. The hyphae of Hysterangium 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 mycorrhizae using benomyl did not affect soil P or oxalate. These data indicate that there are some fundamental differences in chemical exudation between mycorrhizal fungi that could affect P uptake and cycling in arid ecosystems. Received: 7 December 1994