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Interactions entre processus microbiens, cycle des nutriments et fonctionnement du couvert herbacé: cas de la nitrification dans les sols d'une savane humide de Côte d'Ivoire sous couvert à Hyparrhenia diplandra.

Abstract : Soil nitrification is an important process that partly controls nitrogen availability for plants and nitrogen conservation at ecosystem level. This process is particularly critical in nutrient-poor systems like the wet savanna of Lamto (West Africa) where nitrogen is considered as the major factor limiting primary production. Savanna facies dominated by the grass Hyparrhenia diplandra are known to exhibit low levels of nitrification and thus avoid nitrate losses. We used high/low nitrification sites as models to investigate whether vegetation could inhibit nitrification, and the possible consequences in terms of ecosystem performance and nutrient behaviour. We showed that H. diplandra sites exhibiting high- and very low-nitrification potential coexist. Stability of the two systems was suggested through studies of H. diplandra nitrate reductase enzyme, showing different nutrition modalities of the two subpopulations (i.e. from the two sites). Through transplantation experiments, we provided the first in situ evidence of the direct control of nitrification by H. diplandra at subpopulation level, with an inhibition/stimulation balance. This conclusion has been sustained by negative correlations between root density and nitrification in low nitrification site. Aboveground primary production and shoot-root ratio were much lower in high than in low nitrification sites. Size, growth and functional indices of H. diplandra from high-nitrification site were lower in the field and greenhouse compared to H. diplandra from low-nitrification-site. When mixed, they presented decreasing size indices, suggesting a lower competitive ability via lower light resource access. These results suggested lower nitrogen availability in the high nitrification site and existence of distinct grass subpopulations exhibiting intrinsic different structural/functional characteristics. Further studies should deal with inhibition mechanisms, and stability and dynamics of these two contrasted systems.
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Contributor : Jean-Christophe Lata <>
Submitted on : Monday, March 14, 2011 - 7:10:26 PM
Last modification on : Thursday, December 10, 2020 - 12:36:20 PM
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  • HAL Id : tel-00576611, version 1
  • PRODINRA : 246598

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Jean-Christophe Lata. Interactions entre processus microbiens, cycle des nutriments et fonctionnement du couvert herbacé: cas de la nitrification dans les sols d'une savane humide de Côte d'Ivoire sous couvert à Hyparrhenia diplandra.. Ecologie, Environnement. Université Pierre et Marie Curie - Paris VI, 1999. Français. ⟨tel-00576611⟩

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