Photosynthetica 2007, 45(1):30-35 | DOI: 10.1007/s11099-007-0005-5

Variations in daytime net carbon and water exchange in a montane shrubland ecosystem in southeast Spain

P. Serrano-Ortiz^1,*, A. S. Kowalski¹, F. Domingo^2,4, A. Rey², E. Pegoraro², L. Villagarcía³, L. Alados-Arboledas¹

¹ Department of Applied Physics, University of Granada, Granada, Spain

² Arid Zones Research Station (Estación Experimental de Zonas Áridas), CSIC, Almería, Spain

³ Department of Environmental Sciences, University of Pablo Olavide, Sevilla, Spain

⁴ Department of Vegetal Biology and Ecology, University of Almería, Almería, Spain

Carbon and water fluxes in a semiarid shrubland ecosystem located in the southeast of Spain (province of Almería) were measured continuously over one year using the eddy covariance technique. We examined the influence of environmental variables on daytime (photosynthetically active photons, F _P >10 µmol m^-2 s^-1) ecosystem gas exchange and tested the ability of an empirical eco-physiological model based on F _P to estimate carbon fluxes over the whole year. The daytime ecosystem fluxes showed strong seasonality. During two solstitial periods, summer with warm temperatures (>15 °C) and sufficient soil moisture (>10 % vol.) and winter with mild temperatures (>5 °C) and high soil moisture contents (>15 % vol.), the photosynthetic rate was higher than the daytime respiration rate and mean daytime CO₂ fluxes were ca. -1.75 and -0.60 µmol m^-2 s^-1, respectively. Daytime evapotranspiration fluxes averaged ca. 2.20 and 0.24 mmol m^-2 s^-1, respectively. By contrast, in summer and early autumn with warm daytime temperatures (>10 °C) and dry soil (<10 % vol.), and also in mid-winter with near-freezing daytime temperatures the shrubland behaved as a net carbon source (mean daytime CO₂ release of ca. 0.60 and 0.20 µmol m^-2 s^-1, respectively). Furthermore, the comparison of water and carbon fluxes over a week in June 2004 and June 2005 suggests that the timing-rather than amount-of spring rainfall may be crucial in determining growing season water and carbon exchange. Due to strongly limiting environmental variables other than F _P, the model applied here failed to describe daytime carbon exchange only as a function of F _P and could not be used over most of the year to fill gaps in the data.

Keywords: carbon dioxide flux; eddy covariance; phenology; photon flux density; shrubland; water vapour flux

Received: February 17, 2006; Accepted: May 12, 2006; Published: March 1, 2007Show citation