Water consumption of a CO2 enriched poplar stand

he responses of trees to global change, particularly to the predicted increase of atmosphericCO2, will be crucial in determining the ability of planted and natural forests to sequester carbon on a globalscale. Limited information is presently available on the overall behaviour of agro-forestry and forestsystems to enhanced CO2. Objective of this experiment was to determine the response in terms of water useof a cultivated agro-forestry system, to future atmospheric CO2. The FACE facility is located in Tuscania(Viterbo, Central Italy) and the plantation was realized in spring 1999, utilising three different species ofpoplar cuttings. Within the plantation, six 350 m2 plots were treated either with atmospheric or enrichedCO2 concentration (550 ppm); the three enriched plots were equipped with octagonal FACE ringsenclosing a circular area of 21 m in diameter. Evapotranspiration was monitored on ambient and enrichedplots of Populus x euramericana plants - by means of the residual energy balance approach - starting in thesecond decade of August 2001. Net radiation and soil heat flux were measured on 3 replicates for eachtreatment. Canopy radiative temperature was also monitored in these same plots by means of infraredthermometers, while wind and temperature profiles were measured at a single location in the centre of thefield. Sensible heat flux was computed on the basis of air and canopy temperatures and of the aerodynamicresistance - and latent heat flux as the residual of the crop energy balance. The mean daytime canopytemperature of FACE plots increased up to 2 °C, but such differences decreased and were almostundetectable by the end of the measurements, in the first decade of September. During this period, meandaily water consumption decreased from about 8 mm to 6 mm and was 5.6 % lower in FACE plots.