1. Isotopic Composition of Organic and Inorganic Carbon in Desert Biological Soil Crust Systems Kathryn Alexander 1, Hilairy Hartnett 1,2, Ariel Anbar 1,2, Hugo Beraldi 3, Ferran Garcia-Pichel 3 Location Field Sites and Samples Dark, Lichen dominated BSC Light, Cyanobacteria dominated BSC Sunday Churt Site Green Butte Site Dark Crusted-Sunday Churt (09B) Dark Crusted-Green Butte (10J) Light Crusted-Green Butte (10H) Light Crusted-Green Butte(10G) Dark Uncrusted-Sunday Churt (09C) Average Depth (cm)  g (C,N)/mg soil  13C vs VPDB ( ‰ ) Total Carbon Total Nitrogen Inorganic CarbonOrganic Carbon Global distribution of BSCs Cyanobacteria dominated Green algal dominated Lichen dominated Moss/Liverwort dominated (Büdel, 2001) 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 B13C-1116 Carbon (C) Cycle (Adapted from Rost et al., 1998) Nitrogen (N) Cycle N2N2 NH 4 + NO 2 - NO 3 - NO 2 - Denitrification Nitrification Nitrogen Fixation Organic N Compounds Assimilation Mineralization Nitrate Reduction (Adapted from Schink, 1999) How do Biological Soil Crusts manipulate geochemical systems to obtain required nutrients and metals in a chemically and physically stressful environment? Biological Soil Crusts (BSCs) 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 (Belnap et al., 2001) Methods 1)Soil cores collected in March, 2006 2)Samples dried, ground, sieved, and homogenized 3)Analyzed on an elemental analyzer connected to a Finnigan Deltaplus isotope ratio mass spectrometer 4)Organic carbon measured after fuming bulk samples with concentrated HCl 5)Inorganic carbon calculated as the difference between bulk and organic (with full error propagation) 6)20% of samples were analyzed in duplicate 7)Isotope measurements made relative to three laboratory working standards previously calibrated to the VPDB scale by measurement against IAEA standards. Depth Light Heavy Isotopic Composition Organic C Total C Inorganic C Carbon Content Less More Depth Organic C Inorganic C Conceptual Model – Idealized Soil Profile Predictions: 1)Organic C will reflect photosynthetically derived C, -20 to -30 ‰ 2)Inorganic C will be isotopically heavy relative to organic C (i.e., -10 to 0 ‰) Results: 1)In some cores, data support predictions 2)Green Butte cores have heavier C than expected Current Research Directions 1)Higher resolution sampling with depth 2)Direct measurement of inorganic carbon content and isotopic composition 3)Concurrent analysis of clay mineralogy Denitrification Nitrification CO 2 Arid regions of North America (Rosentreter and Belnap, 2001) Cold deserts Hot deserts 1 2 ~ 3 km Map of field sites near Moab, Utah 1)Sunday Chert 2)Green Butte 3)Colorado River (no crust here!) ConsumersProducers Organic C Sedimentary Rock Photo-, Chemosynthesis Respiration Preservation Burial Decomposition Gap in sequence Quartz Orthoclase Calcite Ca-smectite Illite Weight % Minerals Present in Core 10G1 14% Clays 87.7% Non-clays % Clays in Core 10G1 Acknowledgements: A. Michaud, L. Williams, M. Kelly, S. Klonowski, M.Kraft 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. (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 For questions or further information contact Katie Alexander at katiealex@asu.edu 3 Peak Intensity (x10 3 ) 2-Theta (deg) 206050403010 Quartz Calcite Zincite* Illite *Zincite added as a standard Raw Spectrum of Bulk Mineralogy for Core 10G1 16 14 12 10 8 6 4 2 0 Thanks to the National Science Foundation for funding (0525569)! Results Schematic diagram describing a range of geomicrobiological interactions and their components present in Biological Soil Crusts. * Soil crust cutter is 23cm x 28cm Soil crust community extends about 0.5 cm below the soil surface Objective To evaluate influence of BSC on underlying soil mineralogy and geochemistry Sites chosen based on previous work and geomicrobiological data