Impacts of global change on the biogeochemical cycling of water and nutrients in the soil-plant system and consequences for vegetation growth in south-western Siberia

• Main Author: Brédoire, Félix
• Other Authors: Interactions Sol Plante Atmosphère (UMR ISPA), Institut National de la Recherche Agronomique (INRA)-Ecole Nationale Supérieure des Sciences Agronomiques de Bordeaux-Aquitaine (Bordeaux Sciences Agro), Université de Bordeaux, Mark Bakker
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2016
• Subjects: Nitrogen; Soil water budget; Tree-ring; Phosphorus; South-western Siberia; Global change; Snow; Soil temperature; Fine roots; Isotopes; Aspen; Grassland; Sibérie du sud-ouest; Changement global; Levant; Température du sol; Bilan hydrique du sol; Cerne; Phosphore; Azote; Racines fines; Peuplier; Prairie; [SDV.SA]Life Sciences [q-bio]/Agricultural sciences; taiga; Siberia
• Online Access: https://tel.archives-ouvertes.fr/tel-01386679; https://tel.archives-ouvertes.fr/tel-01386679/document; https://tel.archives-ouvertes.fr/tel-01386679/file/BREDOIRE_FELIX_2016.pdf

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. Dans un contexte de changement global, prédire l’évolution de la productivité de la végétation dans le sud-ouest (SO) Sibérien reste un défi du fait d’incertitudes fortes sur les processus régulant la disponibilité en eau et en nutriments. Nous avons mis en évidence des relations entre cycles biogéochimiques, climat et propriétés du sol sur six sites contrastés.La croissance radiale des tiges de peuplier est ...