Litter decomposition and soil organic carbon stabilization in a Kastanozem of Saskatchewan, Canada

Abstract Soil organic C (SOC) accumulation is known to increase by practices of increasing plant residue C inputs, while the SOC stabilization efficiency relative to C inputs is variable. The SOC stabilization efficiency in a Kastanozem soil (up to 21% of C inputs) is much greater than the global average (0.7%). To test whether litter is preserved by transformation into the mineral-associated SOC pool in a Kastanozem soil, we conducted a four-year incubation study of 13C-labeled maize residue in Saskatchewan, Canada. We monitored whether litter residue inputs are transformed and stabilized into the mineral-associated heavy fraction (> 1.60 g cm−3). The litter decomposition rates in our study were the lowest among the global dataset due to the limited microbial activities under cold and arid climate. Fractionation of SOC into light and heavy fractions (  1.60 g cm−3, respectively) and subsequent analysis using nuclear magnetic resonance spectroscopy indicated that both the light and heavy fraction pools of transformed maize litter were enriched by microbial lipids, along with aromatic and carboxylic groups. The heavy fraction exhibited the lower decomposition rates than the light fraction due to selective loss of cellulose. This leads to the greater SOC stabilization in the heavy fraction (14% of the litter input) after the 4-year incubation period, compared to the light fraction (7%). Global temperature-dependency of microbial activities can account for slow litter decomposition under semi-arid and cold prairie, while the high stabilization efficiency of the litter-derived C is supported by microbial transformation and the relatively high capacity of mineral association in Kastanozem soils.