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δ 13 C Variation from Plants to Soil

δ 13 C Variation from Plants to Soil. Jonathan Harris MEA 760 NCSU. δ 13 C within Plants and Soil. C3 Plants depleted ~ 21 – 30 per mil C4 Plants depleted ~ 10 – 15 per mil. Plants at Prarie Ridge, NC. Current Plot currently dominated by bermuda grass, a C4 grass.

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δ 13 C Variation from Plants to Soil

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  1. δ13C Variation from Plants to Soil Jonathan Harris MEA 760 NCSU

  2. δ 13C within Plants and Soil • C3 Plants depleted ~ 21 – 30 per mil • C4 Plants depleted ~ 10 – 15 per mil

  3. Plants at Prarie Ridge, NC • Current Plot currently dominated by bermuda grass, a C4 grass. • Historically maintained as a cow pasture dominated by fescue, with some orchard grass, both C3 grasses. • Area underwent manipulation starting 2 years ago.

  4. The Plant to Soil Transition • How δ13C changes from plant to soil • Disequilibrium factor • Difference in atmospheric CO2 between time of soil carbon production and current plant utilized CO2 • Modern CO2 averages -8 per mil while 30-100 years ago CO2 averaged -6.5 per mil. • Decomposition is likely not a factor

  5. How δ13C changes with depth • Many studies have indicated that δ13C becomes enriched with depth. (Nisselbaum et. al 1974, Deines 1980, Ehleringer et. al 2000) • Also that soil organic matter decreases in size and amount with depth.

  6. What causes this? • 4 hypotheses from Ehleringer et. al 2000 • Atmospheric CO2 change over time • Microbial fractionation during decomposition • Preferential microbial decomposition of litter • Mixing of C in the soil

  7. Plant δ13C Relative to Surface • The mean δ13C of all the plant samples collected was -22.21 per mil • The mean δ13C of all the surface soil samples (PRP-5,7) was -19.33 • Clearly an enrichment has occurred from just the transition of living plant material to soil organic matter.

  8. δ13C change in the Soil Profile • Ignoring the isotopic values or large size plant fragments removed from soil the δ13C changed as follows • O horizon -19.05 per mil • A horizon -18.83 per mil • Ap horizon -15.76 per mil • B horizon -22.94 per mil

  9. Do our results match the model? • All of the data collected matched the idea of soil organic matter becomes enriched in δ13C with an increase in depth. • The one exception was the B horizon which in both samples showed a more depleted δ13C than any other soil.

  10. Conclusions • δ13C decreases with soil depth at Prairie Ridge, NC • Likely a combination of processes • Soil mixing • Disequilibrium effect • A great deal of information can be learned from this site if coupled with a definite time of transition from C3 to C4 dominated.

  11. References • Balesdent et. al, 1993. Site-related δ13C of Tree Leaves and Soil Organic Matter in a Temperate Forest. Ecology 74: 1713-1721. • Ehleringer et. al, 2000. Carbon Isotope Ratios in Belowground Carbon Cycle Processes. Ecological Application 10: 412–422. • Keyworth, Amy J. An Investigation into the Fate of Carbon, Nitrogen, and their Isotopes in a Former Cow Pasture in the Piedmont Region of North Carolina • Yamakura,T. and Sahunalu, P. 1990. Soil Carbon/nitrogen Ratio as a Site Quality Index for Some South-east Aasian Forests. Journal of Tropical Ecology. 6: 371-378.

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