Biogeochemistry of oxalate in the antarctic cryptoendolithic lichen-dominated community

• Published in: Microbial ecology 1993-05, Vol.25 (3), p.305-319
• Main Authors: Johnston, C.G. (Utah State University, Logan, UT.), Vestal, J.R
• Format: Article
• Language: English
• Subjects: ACIDE OXALIQUE; ACIDO OXALICO; Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Biological weathering; DISPONIBILIDAD DE NUTRIENTES; DISPONIBILITE D'ELEMENT NUTRITIF; Dissolution; ELEMENTO PRIMARIO DEL SUELO; Ferrihydrite; FLORA MICROBIANA; FLORE MICROBIENNE; Fundamental and applied biological sciences. Psychology; GEOCHIMIE; GEOQUIMICA; LICHEN; Lichens; LIQUENES; Metal oxides; MINERALISATION; MINERALIZACION; Organic acids; OXALATE; Oxalates; OXALATOS; Oxides; ROCHE MERE; Rocks; Sandstones; Synecology; Terrestrial ecosystems; ZONA FRIA; ZONE FROIDE
• ISSN: 0095-3628; 1432-184X
• DOI: 10.1007/bf00171895

Cryptoendolithic (hidden in rock) lichen-dominated microbial communities from the Ross Desert of Antarctica were shown to produce oxalate (oxalic acid). Oxalate increased mineral dissolution, which provides nutrients, creates characteristic weathering patterns, and may ultimately influence the biological residence time of the community. Oxalate was the only organic acid detectable by HPLC, and its presence was verified by GC/MS. Community photosynthetic metabolism was involved in oxalate production since rates of 14C-oxalate production from 14CO2 were higher in light than in dark incubations. Flaking of the sandstone at the level of the lichen-dominated zone a few millimeters beneath the rock surface can be explained by dissolution of the sandstone cement, which was enhanced by Si, Fe, and Al oxalate complex formation. Added oxalate was observed to increase the solubility of Si, Fe, Al, P, and K. Oxalate's ability to form soluble trivalent metal-oxalate complexes correlated with the observed order of metal oxide depletion from the lichen-dominated zone (Mn Fe Al). Thermodynamic calculations predict that Fe oxalate complex formation mobilizes amorphous Fe oxides (ferrihydrite) in the lichen-dominated zone, and where oxalate is depleted, ferrihydrite should precipitate. Hematite, a more crystalline Fe oxide, should remain solid at in situ oxalate concentrations. Oxalate was not a carbon source for the indigenous heterotrophs, but the microbiota were involved in oxalate mineralization to CO2, since oxalate mineralization was reduced in poisoned incubations. Photooxidation of oxalate to CO2 coupled with photoreduction of Fe(III) may be responsible for oxalate removal in situ, since rates of 14C-oxalate mineralization in dark incubations were at least 50% lower than those in the 2 light. Removal of oxalate from Si, Fe, and Al complexes should allow free dissolved Si, Fe, and Al to precipitate as amorphous silicates and metal oxides