The effects of natural carbon dioxide seepage on edaphic protozoan communities in Campo de Calatrava, Ciudad Real, Spain

The effects of natural carbon dioxide [CO2] seepages or “upwellings” on edaphic protozoan communities at two locations in the Campo de Calatrava district in Spain were studied. The fluxes of CO2 in the soil ranged from 11.46 g m−2 day−1 (ambient) to 117.45 g m−2 day−1 at Cañada site and from 14.64 to 293,508.66 g m−2 day−1 at Sima location. No significant changes in the total abundance of ciliates, flagellates and amoeba with CO2 increases were observed at either of the sites. Nevertheless, the composition and structure of the community of ciliates were significantly affected by CO2. The diversity of the community, calculated by using both the Shannon and the Margalef indexes, decreased as CO2 increased. Equitability (or evenness) and even more so total richness decreased with higher CO2. A shift from Polyhymenophorea (Spirotrichea and Heterotrichea) to Colpodea dominated communities and a decrease in the percentage of rapacious ciliates was observed as CO2 increased. The composition of the ciliate community could therefore be used as a potential indicator of CO2 concentrations in soils.