Isotopic Composition of Organic and Inorganic Carbon in Desert Biological Soil Crust SystemsKathryn Alexander1, Hilairy Hartnett1,2, Ariel Anbar1,2, Hugo Beraldi3, Ferran Garcia-Pichel3
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)
Ave
rage
Dep
th (
cm)
g (C,N)/mg soil 13C vs VPDB (‰)
Total Carbon Total Nitrogen Inorganic Carbon Organic 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
N2
NH4+
NO2-
NO3-NO2
-Denitrification
NitrificationNitrogen Fixation
Organic N CompoundsAssimilation
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, 20062) Samples dried, ground, sieved, and homogenized3) Analyzed on an elemental analyzer connected to a Finnigan Deltaplus isotope
ratio mass spectrometer4) Organic carbon measured after fuming bulk samples with concentrated HCl5) Inorganic carbon calculated as the difference between bulk and organic (with full
error propagation)6) 20% of samples were analyzed in duplicate7) Isotope measurements made relative to three laboratory working standards
previously calibrated to the VPDB scale by measurement against IAEA standards.
Dep
th
Light Heavy
Isotopic Composition
Organic C
Total C
Inorganic C
Carbon Content
Less More
Dep
th
Organic C Inorganic C
Conceptual Model – Idealized Soil ProfilePredictions: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
DenitrificationNitrification
CO2
Arid regions of North America(Rosentreter and Belnap, 2001)
Cold deserts
Hot deserts
1
2
~ 3 km
Map of field sites near Moab, Utah1) Sunday Chert2) Green Butte3) Colorado River (no crust here!)
ConsumersProducers
Organic C
Sedimentary Rock
Photo-, Chemosynthesis
Respiration
Preservation
Burial
Decomposition
Gap in sequence Gap in sequence
Qua
rtz
Ort
hocl
ase
Cal
cite
Ca-
smec
tite
Illite
Wei
ght
%
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 [email protected]
3
Pea
k In
tens
ity (
x103
)
2-Theta (deg)20 6050403010
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.
Atmosphere
Aqueous phase
Biological Components
Solid Phases
Net exports
Emergent properties, lasting signatures
L I GHT
* Soil crust cutter is 23cm x 28cm
Soil crust community extends about 0.5 cm below the soil surface
ObjectiveTo evaluate influence of BSC on underlying soil mineralogy and geochemistry
Sites chosen based on previous work and geomicrobiological data
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