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Universitat de Barcelona (2017)

High mountain dwarf shrubs under climate change : effects of in situ experimental warming, CO2 enrichment and drought on their growth and functioning

Anadon Rosell, Alba

Titre : High mountain dwarf shrubs under climate change : effects of in situ experimental warming, CO2 enrichment and drought on their growth and functioning

Subarbusts d’alta muntanya davant el canvi climàtic. Efectes de l’escalfament, l’enriquiment de CO2 i la sequera experimentals in situ en el seu creixement i funcionament

Auteur : Anadon Rosell, Alba

Université de soutenance : Universitat de Barcelona

Grade : Doctoral Thesis 2017

Résumé
High-elevation and high-latitude ecosystems are expected to be especially vulnerable to global change. Dwarf shrub species cover extensive areas in high mountain ecosystems, and warmer temperatures and land-use change have favoured their expansion. Co-occurring dwarf shrub species may respond differently to climate change, which can have major effects on their interactions, growth and performance, and ultimately lead to drastic changes in plant communities. In this Thesis, warming, CO2 enrichment and drought experiments have been carried out at the ecotone between the subalpine and alpine belts in different study sites across the Pyrenees and the Alps. The objective was to assess how these factors may influence dwarf shrub species interactions, growth, xylem anatomy and C allocation dynamics. Results of this Thesis show species-specific responses to the treatments, and these responses differed in magnitude and direction depending on the treatment applied. Vaccinium myrtillus responded positively to increased temperatures, whereas the co-occurring Vaccinium uliginosum and Empetrum hermaphroditum showed no response. Vaccinium myrtillus growth and functioning was similar across stands differing in neighbouring shrub species and we did not find evidence of alterations in plant-plant interactions with warming. Vaccinium myrtillus responded positively to CO2 enrichment with an increased stem basal area and a lagged increased vessel lumen size and xylem-specific hydraulic conductivity, but hydraulic efficiency decreased with warming. Although there was a correlation between growth and accumulated hydraulic conductivity, the growth-anatomical relationship changed with soil warming and CO2 enrichment, and growth stimulation occurred without immediate accompanying changes in the xylem anatomy. We did not find major effects of the experimental summer drought on V. myrtillus water potential and its allocation of recently assimilated C. However, V. uliginosum showed evidence of mild stress, since its stomatal conductance, water potential and speed of C transfer to belowground organs were reduced under drought. All these results suggest that climate change acts differently on co-occurring species, which may lead to future changes in plant community composition, structure and function

Mots clés : Plantes ; Plantas ; Plants ; Canvis climàtics ; Cambios climáticos ; Climatic changes ; Muntanyes ; Montañas ; Mountains

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Page publiée le 30 janvier 2019, mise à jour le 13 février 2019