Isotopic Composition of Organic and Inorganic Carbon in Desert Biological Soil Crust Systems

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B13C-1116 Isotopic Composition of Organic and Inorganic Carbon in Desert Biological Soil Crust Systems Conceptual Model – Idealized Soil Profile Depth Predictions: Organic C will reflect photosynthetically derived C, -20 to -30 ‰ Inorganic C will be isotopically heavy relative to organic C (i.e., -10 to 0 ‰) Results: In some cores, data support predictions Green Butte cores have heavier C than expected Gap in sequence Gap in sequence Carbon Content Isotopic Composition More Light Less Heavy Total C Inorganic C Depth Organic C Inorganic C Organic C Minerals Present in Core 10G1 Sunday Churt Site Raw Spectrum of Bulk Mineralogy for Core 10G1 Weight % 16 Quartz 14 Calcite Zincite* 12 Illite Illite Quartz 10 Calcite Orthoclase Ca-smectite Peak Intensity (x103) 8 6 4 2 14% Clays 0 % Clays in Core 10G1 10 20 30 40 50 60 2-Theta (deg) *Zincite added as a standard Green Butte Site Schematic diagram describing a range of geomicrobiological interactions and their components present in Biological Soil Crusts. 87.7% Non-clays Light, Cyanobacteria dominated BSC Dark, Lichen dominated BSC Kathryn Alexander1, Hilairy Hartnett1,2, Ariel Anbar1,2, Hugo Beraldi3, Ferran Garcia-Pichel3 1. School of Earth & Space Exploration, Arizona State University; 2. Department of Chemistry & Biochemistry, Arizona State University; 3. School of Life Sciences, Arizona State University Objective How do Biological Soil Crusts manipulate geochemical systems to obtain required nutrients and metals in a chemically and physically stressful environment? To evaluate influence of BSC on underlying soil mineralogy and geochemistry Methods Soil cores collected in March, 2006 Samples dried, ground, sieved, and homogenized Analyzed on an elemental analyzer connected to a Finnigan Deltaplus isotope ratio mass spectrometer Organic carbon measured after fuming bulk samples with concentrated HCl Inorganic carbon calculated as the difference between bulk and organic (with full error propagation) 20% of samples were analyzed in duplicate Isotope measurements made relative to three laboratory working standards previously calibrated to the VPDB scale by measurement against IAEA standards. Carbon (C) Cycle Biological Soil Crusts (BSCs) CO2 • Crucial components of arid ecosystems • Cyanobacteria, algae, lichen, micro-fungi, mosses, and others • Involved in C and N cycling • N fixation • Photosynthesis • Decomposition • Tolerate extremes • UV radiation • Temperature • Desiccation Decomposition Respiration Photo-, Chemosynthesis Results Current Research Directions Producers Consumers Total Carbon Total Nitrogen Inorganic Carbon Organic Carbon Higher resolution sampling with depth Direct measurement of inorganic carbon content and isotopic composition Concurrent analysis of clay mineralogy Burial g (C,N)/mg soil 13C vs VPDB (‰) Organic C Dark Crusted-Sunday Churt (09B) Preservation Sedimentary Rock (Adapted from Rost et al., 1998) Nitrogen (N) Cycle Denitrification NO2- NO3- Nitrate Reduction Denitrification (Belnap et al., 2001) Nitrification N2 NO2- Nitrogen Fixation Nitrification Assimilation Dark Uncrusted-Sunday Churt (09C) Organic N Compounds NH4+ Mineralization (Adapted from Schink, 1999) Field Sites and Samples Location Sites chosen based on previous work and geomicrobiological data Average Depth (cm) Light Crusted-Green Butte(10G) Global distribution of BSCs Cyanobacteria dominated Green algal dominated Lichen dominated (Eberl, 2003) 4) Soil solution organic content, composition and presence of metallophores - Metal acquisition - Metal isotopic fractionation 5) The BIG picture: - Impact of BSCs on biogeochemical cycles - Isotopic or mineralogical biosignatures Moss/Liverwort dominated (Büdel, 2001) Cold deserts Light Crusted-Green Butte (10H) Hot deserts Arid regions of North America (Rosentreter and Belnap, 2001) 2 1 3 Dark Crusted-Green Butte (10J) Acknowledgements: A. Michaud, L. Williams, M. Kelly, S. Klonowski, M.Kraft Thanks to the National Science Foundation for funding (0525569)! References: Belnap, J., Budel, B, and Lange, O.L. (2001) In Biological Soil Crusts: Structure, Function, and Management (ed. J. Belnap and O.L. Lange), pp. 3-30. Springer. Büdel, B. (2001) In Biological Soil Crusts: Structure, Function, and Management (ed. J. Belnap and O.L. Lange), pp. 141-152. Springer. Eberl, D.D. (2003) U.S.G.S. Open-File Report 03-78, Boulder, Colorado, 46 p. Schink, B. (1999) In Biology of the Prokaryotes (ed. J.W. Lengeler, G. Drews, and H.G. Schlegel), pp. 804-814. Blackwell Science. Rosentreter, R. and Belnap, J. (2001) In Biological Soil Crusts: Structure, Function, and Management (ed. J. Belnap and O.L. Lange), pp. 31-50. Springer. Rost, T.L., Barbour, M.G., Stocking, C.R., and Murphy, T.M. (199) Plant Biology. Wasdsworth. ~ 3 km * Soil crust cutter is 23cm x 28cm Map of field sites near Moab, Utah Sunday Chert Green Butte Colorado River (no crust here!) Soil crust community extends about 0.5 cm below the soil surface For questions or further information contact Katie Alexander at katiealex@asu.edu