Mass and energy flux measurements over grapevine using micrometeorological techniques

The contribution of soil and vegetation CO2 fluxes to global carbon balance in tree and vine crop ecosystems needs investigation. In the last decade, the eddy covariance (EC) technique was accepted as a standard for estimating carbon and water vapour exchanges by all international flux networks. EC provides a direct measurement of energy and mass flux that uses high frequency measurements of scalars and the vertical component of wind speed. The newer surface renewal (SR) method, however, offers an alternative technique to measure fluxes. This paper reports the results from flux experiments conducted during 2005 over a vineyard ecosystem located in Tuscany (Italy) during the fruit set and veraison phenological stages. Half-hourly measurements of CO2 flux (Fc) and latent heat flux density (LE) were made using an EC system. Estimates of Fc and LE were also obtained using the SR method. In addition, net radiation (Rn) and soil heat flux density (G) data were collected, and the energy balance closure was good. Partitioning of available energy into sensible heat flux density (H) and LE was related to weather conditions and irrigation applications. The Bowen ratio values varied from 0.3 to 0.5 indicating that the plant water status was good. Daytime Fc values ranged between -5 and -8 micro-mol CO2 m-2 s-1, and the daily net C budget was positive, showing that the vineyard was a sink for C over the period studied.