Goldschmidt 2013

© University of Reading 2013 www.reading.ac.uk

Geography and Environmental Science

August 28, 2013

The role of earthworm-produced CaCO3 in the terrestrial carbon cycle Mark E. Hodson, Emma A. A. Versteegh & Stuart Black

The role of earthworm-produced CaCO3 in the terrestrial carbon cycle

Earthworm secreted CaCO3 granules

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Canti (2007) Versteegh et al. (2013)


How are the granules produced?

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Darwin (1881) / Canti & Piearce (2003)

•  Calciferous glands

• Milky fluid

• → CaCO3 concretions

• → granules


Why do they produce them?

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•  “It is probable that they primarily serve as organs of excretion, and secondarily as an aid to digestion” (Darwin, 1881)

•  Egg formation?

•  Triturate food in gizzard?

•  Absorption of food products?

•  Water regulation → evolutionary adaptation to terrestrial habitat?

•  Excretion of toxic cations?

•  pH regulation / eliminate excess CO2?


What are they made of?

•  Calcite

•  Amorphous calcium carbonate (ACC)

•  (some aragonite / vaterite)

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Backscattered SEM

Electron backscatter diffraction (EBSD) crystallographic orientation


Questions

• What is the carbon sequestration potential of earthworms? –  Influence of temperature –  Influence of [CO2] on CaCO3 production rates

• What are the sources of carbon in earthworm CaCO3 granules? –  Food / organic matter –  CO2

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Lumbricus terrestris – lob worm

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Experiment 1

•  3 soils

•  3 types of water (England, Fiji, Norway)

•  5 temperatures (3, 10, 16, 18, 20 °C)

•  3 weeks acclimatisation

•  1 month

•  6 replicates

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Experiment 2

•  1soil; 1 type of water, 1 temperature (16 °C)

•  4 [CO2] (low, medium, high, ambient)

•  3 weeks acclimatisation + 1 month experiment

•  6 replicates

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Analyses •  CaCO3 production

•  [CO2] (ppm)

•  δ13C values of: –  Soil organic matter –  Food (horse manure) –  Soil CO2

–  Earthworm body wall tissue

–  Calciferous gland tissue –  Milky fluid –  Granules in pouches –  Granules in soil

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A δ18O-based palaeothermometer

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1000 ln α = 20.21 (103 T-1) - 38.58


At what rate are granules produced?

•  0.8-2.9 mg/individual/day

•  Larger worms produce more

• Well-fed worms produce more

• High-pH soils yield more

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Lambkin et al. (2011)


CaCO3 production and temperature

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CO2 concentrations

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CaCO3 production and CO2

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δ13C values

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δ13C values of CO2

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δ13C values of earthworm tissues

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δ13C values of CaCO3

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δ13C values of CO2 and CaCO3

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Contribution to C sequestration •  CaCO3 production: 0.49-3.64

mg/individual/day

•  Typical population density: ~15 individuals/m2 (max 62)

•  CaCO3 production: ~113 kg/ha/y

•  C sequestration: ~45 kg C/y/ha (max. 329)

•  ~ 1% of total soil carbon

•  < 0.5 % of UK C emissions

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Conclusions •  CaCO3 production by L. terrestris increases with temperature;

•  CaCO3 production is higher at higher [CO2];

•  There is no relationship between δ13C values of earthworm tissues and the CaCO3 produced;

•  A decrease in δ13C values of milky fluid → granules in pouches → granules in soil probably reflects transformation of ACC into calcite;

•  δ13C values of soil CO2 and granule CaCO3 are correlated, indicating a direct contribution of CO2 to the granules;

•  Earthworm-produced CaCO3 forms only a minor contribution to C sequestration in soils.

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Thank you!

Questions?

Versteegh EAA, Black S, Canti MG, Hodson ME (2013) Earthworm-produced calcite granules: a new terrestrial palaeothermometer? Geochimica et Cosmochimica Acta, 10.1016/j.gca.2013.06.020

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