Minéralisation de l'azote et nitrification dans les écosystèmes forestiers : Effet du type de sol et de l'essence forestière

Abstract : The aim of this thesis was to identify the main indicators of N availability in forest soils and thereafter to determine mechanisms by which tree species control soil N mineralization and nitrification. Various indicators of N availability were compared within 50 beech forests covering a large range of soil types in northeastern France. Thereafter, the effect of six tree species was studied in an acidic cambisol hyperdystric at the experimental site of Breuil (Morvan, France). Potential net N mineralization was negatively correlated with soil pH and positively with microbial C/N ratio. Percent nitrification was strongly correlated with the combination of soil pH and soil C/N or with the combination of Ellenberg's indices of N availability or Ecoplant C/N and Ellenberg's indices of acidity (R) based on the vegetation community composition. At the Breuil experimental site, the percent nitrification was high in beech, Corsican pine and Douglas fir plantations whereas it was very low in the Nordmann fir and the spruce plantations and the native forest stands (an old coppice with standard dominated by beech and oak). The exchange of soil cores between stands showed that under the « High nitrifying stands », root colonization was low and percent nitrification was quickly stimulated (<16 months). In « Low nitrifying stands », root colonization was very quick but percent nitrification decreased slowly (>28 months). Percent nitrification was quickly stimulated by clear felling of the native forest. Our results converge toward a strong influence of roots on the nitrogen cycle in forest ecosystems but it needs further efforts to identify the mechanism.
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Hasaina Sitraka Andrianarisoa. Minéralisation de l'azote et nitrification dans les écosystèmes forestiers : Effet du type de sol et de l'essence forestière. Sciences agricoles. Université Henri Poincaré - Nancy 1, 2009. Français. ⟨NNT : 2009NAN10007⟩. ⟨tel-01748509⟩

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