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Certain millet genotypes store more carbon in the soil than others

Relying on isotopic measurements, a collaboration involving BIAM (CEA-CNRS-AMU) and the LSCE (CEA-CNRS-UVSQ) has succeeded in quantifying the amount of carbon released into the soil by the roots of millet after only a few weeks of growth. The researchers were thus able to identify millet genotypes (lines) that offer optimal carbon storage while preserving the older carbon stocks already present in the soil.

Published on 15 March 2022

Promoting carbon storage in soils through virtuous agricultural practices has a dual advantage:

  • it reduces atmospheric CO2 levels and thus contributes to climate change mitigation
  • it increases soil fertility

With this in mind, researchers from BIAM and the LSCE, in collaboration with the IRD and the University of Montpellier, chose to study millet, a cereal grown primarily in Africa and India. Specifically, they compared different lines whose roots aggregate soil particles more or less efficiently. This property of "rhizospheric aggregation" is known to allow plants to adapt to stresses, in particular water stress.
The biologists grew four lines of Pennisetum glaucum millet (C4 type) in soil dominated by the organic material from C3 plants. After four weeks of growth, they evaluated:

  • The ratio of root-adhering soil mass (rhizosheath) to root tissue biomass was found to be significantly variable between the lines: this is indicative of the plant's ability to deposit carbon in the soil.
  • Carbon isotope measurements (13C and 14C) in roots and soil were used to quantify the transfer of carbon from the roots to the soil at an early stage of millet growth, and to assess how much of the "old" carbon was respired by soil microorganisms under the stimulating effect of an influx of "fresh" organic matter (known as the priming effect).
  • Using a model, the researchers were able to quantify this priming effect for all millet lines and show that it is lower for lines with a high rhizospheric aggregation.

Millet lines whose roots have aggregated more soil particles are therefore able to input more carbon in the soil, and among the high-aggregation lines, one was pointed out as best preserving the old soil carbon from overconsumption by soil microorganisms.

In a subsequent stage, the identification of genes controlling rhizospheric aggregation could pave the way for varietal selection programs designed to promote soil carbon storage. 

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