Continuous soil carbon storage of old permanent pastures in Amazonia

Stahl Clément, Fontaine Sébastien, Klumpp Katja, Picon-Cochard Catherine, Grise Marcia Mascarenhas, Dezécache Camille, Ponchant Lise, Freycon Vincent, Blanc Lilian, Bonal Damien, Burban Benoit, Soussana Jean-François, Blanfort Vincent. 2017. Continuous soil carbon storage of old permanent pastures in Amazonia. Global Change Biology, 23 (8) : 3382-3392.

https://doi.org/10.1111/gcb.13573

Article de revue ; Article de recherche ; Article de revue à facteur d'impact

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Url - éditeur : http://onlinelibrary.wiley.com/doi/10.1111/gcb.13573/full

Quartile : Outlier, Sujet : ENVIRONMENTAL SCIENCES / Quartile : Outlier, Sujet : BIODIVERSITY CONSERVATION / Quartile : Outlier, Sujet : ECOLOGY

Résumé : Amazonian forests continuously accumulate carbon (C) in biomass and in soil, representing a carbon sink of 0.42–0.65 GtC yr−1. In recent decades, more than 15% of Amazonian forests have been converted into pastures, resulting in net C emissions (~200 tC ha−1) due to biomass burning and litter mineralization in the first years after deforestation. However, little is known about the capacity of tropical pastures to restore a C sink. Our study shows in French Amazonia that the C storage observed in native forest can be partly restored in old (≥24 year) tropical pastures managed with a low stocking rate (±1 LSU ha−1) and without the use of fire since their establishment. A unique combination of a large chronosequence study and eddy covariance measurements showed that pastures stored between −1.27 ± 0.37 and −5.31 ± 2.08 tC ha−1 yr−1 while the nearby native forest stored −3.31 ± 0.44 tC ha−1 yr−1. This carbon is mainly sequestered in the humus of deep soil layers (20–100 cm), whereas no C storage was observed in the 0- to 20-cm layer. C storage in C4 tropical pasture is associated with the installation and development of C3 species, which increase either the input of N to the ecosystem or the C:N ratio of soil organic matter. Efforts to curb deforestation remain an obvious priority to preserve forest C stocks and biodiversity. However, our results show that if sustainable management is applied in tropical pastures coming from deforestation (avoiding fires and overgrazing, using a grazing rotation plan and a mixture of C3 and C4 species), they can ensure a continuous C storage, thereby adding to the current C sink of Amazonian forests.

Mots-clés Agrovoc : forêt, forêt tropicale, déboisement, pâturages, séquestration du carbone, cycle du carbone, émission atmosphérique, matière organique du sol, litière forestière, écosystème forestier, plante fourragère, utilisation des terres