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Impacts du changement global sur les cycles biogéochimiques de l’eau et des nutriments dans le système sol–plante et conséquences pour la croissance de la végétation en Sibérie du sud-ouest

Abstract : Predicting the evolution of vegetation productivity in SW Siberia in the contextof global change remains a challenge because of major uncertainties concerningthe biogeochemical cycling and the plant-availability of water and nutrients. Weprovided insights on their relation to climate and soil properties, investigating sixcontrasting sites.Aspen stem radial growth is mainly sensitive to soil water budget in the foreststeppezone established in the south of SW Siberia while it is enhanced by highsummer temperatures in the sub-taiga, in the north of the region.Field measurements and water budget simulations revealed that snow-melt isimportant re-filling soil water reserves in the south. In the north, these reservesare mostly re-filled in autumn and snow-melt is associated with drainage. A thicksnow-pack also prevents soil from freezing in winter in the sub-taiga. Water deficitand soil freezing largely impact the distribution of fine roots within the soil profilewhich is deeper in forest-steppe than in sub-taiga.The homogeneous soil phosphorus (P) status in the region investigated revealedthis nutrient has not been yet very impacted by contrasting soil processes. High Pstocks, and in particular plant-available forms, suggest P is unlikely to be limitingunder current and future conditions.By contrast, we found differences in nitrogen (N) status. Above-ground litterdecay and the release of N occurs faster in sub-taiga than in forest-steppe. Higherdrainage may explain deeper N transfer in sub-taiga soils. However, sub-taiga soilsalso seem to be efficient in retaining N, limiting losses from the soil–plant system.
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Submitted on : Monday, October 24, 2016 - 2:33:06 PM
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Félix Brédoire. Impacts du changement global sur les cycles biogéochimiques de l’eau et des nutriments dans le système sol–plante et conséquences pour la croissance de la végétation en Sibérie du sud-ouest. Sciences agricoles. Université de Bordeaux, 2016. Français. ⟨NNT : 2016BORD0033⟩. ⟨tel-01386679⟩

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