Mineralization Potential and Temperature Sensitivity of Soil Organic Carbon under Different Land Uses in the Parkland Region of Alberta, Canada

The temperature sensitivity of soil organic C contained in different particle-size fractions is important in the context of global climate change but to date has been poorly studied. We compared the effects of temperature (7, 14, and 21 degrees C) on C mineralization rates in fractionated soils from four land use systems [agriculture, AG; plantation; grassland, GRA; and native aspen (Populus tremuloides Michx.) stand, NAT] in the parkland region of Alberta, Canada, over a 370-d laboratory incubation. Carbon was largely held in the fine (<53 mu m) fraction (59%), followed by the medium (53-250 mu m, 31%) and coarse (250-2000 mu m, 10%) fractions. Across land uses and incubation temperatures, the amount of C mineralized from bulk soil over 370 d ranged between 2 and 9% of initial total organic carbon (C-i), with mineralization rates based on per unit of C-i ranging from 0.4 to 5.8 x 10(-4) mg C mg(-1) C-i d(-1) and mean residence times (MRTs) ranging from 15 to 65 yr. Of the total amount of C mineralized, 77, 14, and 9% came from the coarse, medium, and fine fractions, respectively. The temperature sensitivity (Q(10)) of organic C under NAT increased with decreasing particle size, while plantation-and GRA-derived soil organic C showed significantly greater Q(10) in the medium and fine fractions only. We conclude that the mineralization potential and temperature sensitivity of soil organic C in the studied land use systems were controlled mainly by organic matter quality and physical protection provided through aggregation and adsorption.