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Università degli studi della Tuscia - Viterbo (2012)

Impatto dell’aumento di temperatura e dei periodi siccitosi sui flussi di carbonio in un arbusteto mediterraneo

Guidolotti, Gabriele

Titre : Impatto dell’aumento di temperatura e dei periodi siccitosi sui flussi di carbonio in un arbusteto mediterraneo

Impact of increased temperature and drought on carbon fluxes in a Mediterranean shrubland

Auteur : Guidolotti, Gabriele

Université de soutenance : Università degli studi della Tuscia - Viterbo

Grade : Dottorato di ricerca in Ecologia forestale 2012

Résumé
Arid and semiarid woody shrubland ecosystems make up between 30 and 45% of the global terrestrial surface area, 24% of the global organic carbon and 16% of the global aboveground biomass. Despite their potential impact on the global carbon balance, these ecosystems and their responses to the climate change are still poorly understood. The aim of this thesis was to investigate the impact of increased temperatures and reduced water input from precipitation on the functionality of Mediterranean shrubland (garigue). A microclimatic manipulation was performed in 9 experimental plots (about 25 m2) with an automatic roof that cover the vegetation during the night increasing about 1°C the minimum soil and air temperature (Warming treatment, 3 plots) and during rain events reducing of about 20% the precipitation input (Drought treatment, 3 plots), the remaining 3 plots were used as control. A manual and modular canopy chamber was developed for gas-exchange determination. The several tests carried out in the chamber estimated that the leaks introduced an error of 1% in the flux computation, the attenuation of visible radiation due to the chamber walls was only about 10% and there were not sensible pressure variations. The chamber was used, inside the experimental plots, to monitor NEE (Net Ecosystem Exchange) and TER (Total Ecosystem Respiration). GPP (Gross Primary Production) was estimated as difference between NEE and TER. Soil CO2 efflux (SR) was monitored by a commercial chamber. All the C fluxes examined showed a strong temporal variation with the highest rates during the spring, where the high water content and the mild temperature supported both the photosynthetic and respiratory activity, lower rates were recorded during the hot dry non-vegetative summer season. The autumnal rains enhanced SR and TER more than GPP, is in this period that NEE rich the minimum values. At the same microclimatic conditions, drought treatment did not affect significantly the C fluxes ; this underlined the high resilience of this ecosystem to water stress. The warming treatment influenced productivity (GPP and NEE) during the periods with lower temperatures and higher soil water content. The statistical regression approach, allowed to fill the discontinuity of the measurements, highlighted the marked reduction of GPP on drought plots. The application of a respiration model based on temperature and soil water content, allowed an estimation of the temperature sensitivity of respiration (Q10). The Q10 was lower in the wet growing season (1.54) and higher in the hot arid dormant season (2.11). Although this temporal variation was not noticed in the drought plots, the total annual C loss from soil was unchanged among treatments (on average 969 g C m-2 y-1)

Mots Clés : Arbusteto mediterraneo, CO2 fluxes, Drought, Flussi di CO2, Mediterranean shrubland, Riscaldamento notturno, Siccità, Warming

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Page publiée le 12 janvier 2014, mise à jour le 15 mars 2019