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Universidade Federal de Viçosa (2014)

Análise sazonal dos fluxos de CO 2 , energia e vapor d’água sobre um ecossistema de caatinga preservada em um ano seco em Petrolina-PE

Souza, Luciana Sandra Bastos

Titre : Análise sazonal dos fluxos de CO 2 , energia e vapor d’água sobre um ecossistema de caatinga preservada em um ano seco em Petrolina-PE

Seasonal analysis of CO 2 fluxes, energy and water vapor over a Caatinga ecosystem preserved in a dry year in Petrolina-PE

Auteur : Souza, Luciana Sandra Bastos

Université de soutenance : Universidade Federal de Viçosa

Grade : Doutorado em Meteorologia Agrícola 2014

Résumé
The objective of this study was to analyze the seasonal behavior of the carbon, energy and water fluxes, and the diurnal patterns of gas exchange of species occurring in an area of Caatinga preserved. The experiment was conducted at Embrapa Semi-Arid (9,05o S ; 40,19o W ; 350m), in the city of Petrolina, PE, during the year 2012, which was characterized by the occurrence of climatically long period of drought, when rained only 92 mm. Fluxes of carbon, energy and water were measured using the Covariância dos vórtices turbulentos system coupled with a micrometeorological tower of 16 meters. Over time measurements of water content in soil and the coverage index (CI) were made, as well as campaigns to determine the diurnal variation of gas exchange (photosynthesis, transpiration and stomatal conductance) of the five most common species in the experimental area (Poincianella microphylla (Mart. ex G. Don) LP Queiroz, Croton conduplicatus Kunth, Bauhinia cheilantha (Bong.) Steud., Manihot pseudoglaziovii (Pax & Hoffman), Commiphora leptophloeos (Mart.) Gillett). The campaigns were conducted in four different dates with different water availability in the range of measurements of two hours. From the experimental data we determined the radiation balance and CO 2 fluxes (NEE), latent heat (LE), sensible heat (H) and soil heat in seasonal scale and on specific days (depending on IC and of cloudy conditions), as well as the fractions of photosynthetically active radiation absorbed and intercepted. The interaction between the atmosphere and the vegetation in the exchange of water vapor was performed by means of the decoupling factor (Ω) of the surface resistance and aerodynamics. LE values were integrated to obtain the daily evapotranspiration. The data was partitioned NEE through the application of mathematical models for determination of the gross primary productivity and respiration of the ecosystem. The results revealed that the seasonality of water availability during the year 2012 influenced the pattern of the radiation balance and energy, maximizing H / Rn ratio ( 77%) (where, Rn is the net radiation). Thus, evapotranspiration under conditions of severe drought was dependent on the vapor pressure and the surface control deficit, demonstrating a strong coupling of the vegetation with the atmosphere ( 0.04 Ω). However, this interaction varied in response to the progress of water stress after rain events, when the efficiency of water use species was optimized, even with the intense reduction of the assimilation of carbon dioxide. The species P. microphylla, C. conduplicatus, cheilantha B. and M. pseudoglaziovii showed greater optimization of water use as a function of time of day and seasonal water availability conditions. The Caatinga ecosystem preserved acted during a climatically dry year as a source of carbon to the atmosphere, with an emission equal to 468.18 gC m -2 year -1

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