Articles | Volume 13, issue 4
Biogeosciences, 13, 1269–1286, 2016
https://doi.org/10.5194/bg-13-1269-2016
Biogeosciences, 13, 1269–1286, 2016
https://doi.org/10.5194/bg-13-1269-2016

Research article 01 Mar 2016

Research article | 01 Mar 2016

Unambiguous evidence of old soil carbon in grass biosilica particles

Paul E. Reyerson1,2,a, Anne Alexandre3, Araks Harutyunyan1, Remi Corbineau3, Hector A. Martinez De La Torre1, Franz Badeck4, Luigi Cattivelli4, and Guaciara M. Santos1 Paul E. Reyerson et al.
  • 1Earth System Science, University of California, Irvine, USA
  • 2Department of Botany, University of Wisconsin-Madison, USA
  • 3Aix Marseille Université, CNRS, IRD, CEREGE UM34, 13545 Aix-en-Provence CEDEX 4, France
  • 4Consiglio per la Ricerca in Agricoltura e l'analisi dell'economis agraria – Genomics Research Centre, Fiorenzuola d'Arda, Italy
  • acurrent address: Department of Geography and Earth Science, University of Wisconsin-La Crosse, USA

Abstract. Plant biosilica particles (phytoliths) contain small amounts of carbon called phytC. Based on the assumptions that phytC is of photosynthetic origin and a closed system, claims were recently made that phytoliths from several agriculturally important monocotyledonous species play a significant role in atmospheric CO2 sequestration. However, anomalous phytC radiocarbon (14C) dates suggested contributions from a non-photosynthetic source to phytC. Here we address this non-photosynthetic source hypothesis using comparative isotopic measurements (14C and δ13C) of phytC, plant tissues, atmospheric CO2, and soil organic matter. State-of-the-art methods assured phytolith purity, while sequential stepwise-combustion revealed complex chemical-thermal decomposability properties of phytC. Although photosynthesis is the main source of carbon in plant tissue, it was found that phytC is partially derived from soil carbon that can be several thousand years old. The fact that phytC is not uniquely constituted of photosynthetic C limits the usefulness of phytC either as a dating tool or as a significant sink of atmospheric CO2. It additionally calls for further experiments to investigate how SOM-derived C is accessible to roots and accumulates in plant biosilica, for a better understanding of the mechanistic processes underlying the silicon biomineralization process in higher plants.

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We characterize the origin of carbon (C) in phytoliths (biosilica of higher plants) by a multi-isotope approach. We show that phytoliths occlude soil organic C adsorbed through the roots, making them unsuitable for paleo-proxy studies, 14C dating or atmospheric CO2 sequestration. Our findings are in parallel with recent soil paradigm shifts showing that soil microbes access old C and therefore call for further investigations on the role of old C in root–plant interactions and biomineralization.
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