Temporal Dynamics of CO2 Fluxes over a Non-Irrigated Vineyard

Some knowledge gaps still remain regarding carbon sequestration in non-irrigated agroecosystems, where plants may experience drought stress during summertime. Therefore, by the combination of the eddy covariance (EC) and soil chamber techniques, we determined the role of a non-irrigated grassed vineyard in carbon sequestration in the Slovak Republic. Based on the EC data, the cumulative net uptake of CO2 (NEE) for the whole growing season was weak and was ca. −97 (g C m−2). This value resulted from −796 (g C m−2) carbon uptake from the atmosphere through photosynthesis (GEE) and 699 (g C m−2) carbon released to the atmosphere through respiration (Reco). Carbon emissions through Reco were considerable and accounted for ca. 88% of GEE, which points out the importance of Reco for managing non-irrigated agroecosystems. Data from the soil chamber indicated that ca. 302 g C m−2 was released by the vineyard through soil respiration (Rsoil) over a growing season, which was constantly lower than Reco and accounted for ca. 44 ± 18% of Reco. This finding implies that the vineyard soil was not a main source of carbon emissions. Rsoil was mainly driven by temperature (exponentially ca. 69–85%). Meanwhile, vapour pressure deficit (VPD) and temperature appeared to be the most important limiting factors for GEE, NEE, and Reco, particularly when they exceeded a certain threshold (e.g., temperature > 17 °C, and VPD > 10 hPa).