Organic carbon storage and stable isotope composition of soils along a grassland to forest environmental gradient in Saskatchewan

Abstract

Limited information is available about soil organic carbon accumulation rates and stable isotope composition in the boreal region of the Canadian prairies. The objectives of the study were to document soil development, measure carbon storage and accumulation rates, and determine the 13C/12C ratio of organic matter in native prairie soils in the major soil-climatic zones of Saskatchewan. The mean thickness of the Ah horizon increases from 5 cm in the Brown Chernozems to 14 cm in Black Chernozems, and this horizon is absent in Gray Luvisols. The thickness and degree of development of B horizons increase from Brown to Gray soils. Total organic C storage to 1.2 m depth in Brown, Dark Brown, Black Chernozems, and Gray Luvisols is 9.08, 11.72, 14.88, 9.63 kg C m-2, respectively. The long-term mean annual accumulation rates of organic C for Brown, Dark Brown, Black, and Gray soils are 0.57, 0.90, 1.18, and 0.84 g m-2 yr-1, respectively. For a Rego Black Chernozem the rate is 1.83 g m-2 yr-1. All these values are higher than those reported for temperate grasslands in the United States of America. The ỏ13C values of organic C (an average of all profiles in each soil zone to 1.2-m depth) range from -22.9 ‰ for Dry Brown soils, -24.3‰ for Brown soils, -24.8‰ for Dark Brown soils, -25.3‰ for Black soils, and -26.8‰ for Gray soils. The relative contribution of C4 plants to soil organic C decreases from the warm semiarid grassland to the moist Boreal region, where C4 plants have not influenced organic C at all. Considering the net primary production (NPP) estimated for the soil zones, average aboveground carbon sequestration is estimated to be about 0.46% of NPP. These data provides a realistic assessment of C balances in native prairie soils of Saskatchewan. Key words: Rate of carbon accumulation, stable isotope of soil carbon, soil zones of Saskatchewan, grassland soils, forest soils, Rego Black Chernozem soils