Search

Purpose: The objective of this study is to estimate the contribution of various sources that influence soil CO concentrations in calcareous grassland. Materials and methods: The research was performed at the Podgorski Kras plain (45 °33′ N, 13 °55′ E, 400-430 m.a.s.l.) in the sub-Mediterranean region of Slovenia (SW Slovenia), where many meadows and pastures have been abandoned. In parallel to the measurement of soil respiration R, soil gas was sampled for stable isotope analysis. Samples were taken biweekly at two sites, Grassland and Invaded, from July 2008 until November 2010. In addition, daily variations in concentration and stable isotope composition of soil CO were determined in May 2009. The partitioning of soil CO concentrations was performed using stable isotope mass balance calculation. Results and discussion: The concentration and isotope composition of soil CO exhibited similar seasonal variations at both sites. Lower δC values, ranging from −28.2 to −15.2 ‰, which occurred during warm periods and higher values, up to −12.1 ‰, were typical of cold winter periods, from December to March. Organic sources were estimated to constitute between 78 and 99 % of total soil CO during warmer periods from May until October. This contribution was lower during the winter, ranging from 46 to 77 %. In winter, the atmospheric component to soil CO dominated, constituting up to 60 %. On average, the inorganic contribution was estimated to comprise 12 % of the soil CO at all sampling locations. The contribution of this source to soil CO concentration, at up to 41 %, was highest in Grassland during the growing season. The inorganic source of soil CO was also an important component during daily variations. The highest contribution was observed during the day, in parallel to the highest respiration rates. Conclusions: The inorganic pool is shown to be an important part of soil CO in calcareous areas and should be considered as equal to organic CO as a source in soil CO partitioning. [ABSTRACT FROM AUTHOR]