Impact of snow cover duration on biogeochemical cycles in alpine tundra

• Main Author: Baptist, Florence
• Other Authors: Laboratoire d'Ecologie Alpine (LECA), Université Joseph Fourier - Grenoble 1 (UJF)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS), Université Joseph-Fourier - Grenoble I, Serge Aubert; Philippe Choler([e-mail])
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2007
• Subjects: biogeochemical cycles; carbon cycle; alpine ecosystems; productivity; litter decomposition; cycles biogéochimiques; cycle du carbone; écosystèmes alpins; neige; productivité; décomposition des litières; [SDV.BV]Life Sciences [q-bio]/Vegetal Biology; Arctique*; Tundra
• Online Access: https://theses.hal.science/tel-00376004; https://theses.hal.science/tel-00376004/document; https://theses.hal.science/tel-00376004/file/These_FBaptist.pdf

Alpine tundra store large carbon stocks in their soils. In these ecosystems, the local mesotopography determines snow cover distribution, a key variable, which affect the edapho-climatic conditions on the short term (direct effects) and, in the longer-term, select for contrasting plant and microbial communities at both ends of the topographical gradient (indirect effects). In the context of global change, where large changes in snow precipitations are projected, this study explores the controls exerted by snow cover on carbon fixation and carbon mineralization in alpine tundra. Edapho-climatic variables (water and temperature) were measured during several years and we used vegetation functional characteristics (using plant functional traits) to quantify the indirect effects of snow cover on biogeochemical cycles. Various approaches (in situ measurements, experimental manipulations and modeling) were used. This study demonstrates that carbon fixation along mesotopographical gradients is determined by plant functional traits, canopy properties and growing season length. A longer growing season may lead to a marked increase in primary production, if freezing events at snowmelt remain infrequent. In contrast, carbon mineralization is mainly dependant over soil organic matter quality. Shifts in plant functional traits, in particular those related to litter lignin content, will strongly impact the degradation process. Finally, the quantification of carbon and nitrogen fluxes in plants and at the plant-soil interface reveals a tight spatial and temporal coupling which is essential for species whose growth is limited by growing vegetation length. This coupling is reduced in plant communities which benefit from a longer growing season. The evolution of carbon fluxes and stocks in alpine ecosystems is discussed in the context of climatic changes. Les écosystèmes alpins, au même titre que les écosystèmes arctiques, séquestrent des quantités importantes de carbone dans leurs sols. Dans ces écosystèmes, la topographie ...