Abstract

MATEUS, João; PITA, Gabriel; RODRIGUES, Abel  and  OLIVEIRA, Hélène. Seasonal Evolution of the Evapotranspiration Regime and Carbon Assimilation Over a Eucalyptus globulus Plantation. Silva Lus. [online]. 2006, vol.14, n.2, pp.135-147. ISSN 0870-6352.

Seasonal patterns of carbon assimilation and evapotranspiration of 2004 in Eucalyptus globulus plantation of the CarboEurope-IP Portuguese site of Herdade da Espirra are discussed. The atmospheric fluxes were obtained by the eddy covariance method. A separation of atmospheric carbon flux, or net ecosystem exchange (NEE), in gross primary production (GPP) and ecosystem respiration (R_eco), was made and analysed the variation of atmospheric fluxes with some micrometeorological variables. The plantation acted as a strong carbon sink, with a NEE of 7.9tonC.ha^-1.yr^-1. The diurnal NEE was mainly a function of global solar radiation, with which it is perfectly in phase all year around, except for the period between July and September. In these months, stomatal closure, strongly dependent on the water vapour pressure deficit in the atmosphere (WVD) high values and low water availability, was the main factor controlling carbon assimilation, a tendency already noticed in 2002 and 2003. The evapotranspiration is clearly controlled by water vapour deficit with decoupling factors ( Ω ) varying from 0.1 to 0.4, typical data for forest canopies. In the period from July to September evapotranspiration dependency on WVD increases as a consequence of the stomatal closure.

Keywords : seasonal patterns; evapotranspiration; carbon; radiation; vapour pressure.

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