Biological But Not Thermal Stability of Soil Organic Carbon Differs between Two Agroforestry Systems and Their Component Land-Uses in Western Canada

Agroforestry systems play important roles in increasing carbon (C) sequestration and mitigating climate change in western Canada. However, the effect of different agroforestry systems and their component land-uses on soil organic C (SOC) stability is poorly understood. We studied SOC stability in surface (0-10 cm) soils from two agroforestry systems (shelterbelts and hedgerows) and their component land-uses (forest and cropland) in central Alberta, Canada. Laboratory incubation was used to assess biological SOC stability, and compared to thermal SOC stability measured during ramped combustion. The shelterbelt system had higher cumulative soil respiration and SOC loss during incubation, and thus lower biological stability than the hedgerow system. Cumulative respiration and SOC loss during incubation in forest land-use was 1.63 and 1.57 times that in the cropland, indicating lower biological stability in the former. Thermal stability indicators, CO 2 -T 50 (the temperature at which half of the CO 2 is produced), DSC-T 50 (the temperature at which half of the exothermic energy is released) and ROI (return on energy investment) were influenced by the interactive effects of the agroforestry system by land-use, while TG-T 50 (the temperature at which half of the exothermic mass is lost) and Ed (energy density) were influenced by land-use and the interactive effects of agroforestry system by land-use. Planting trees in agricultural land to form agroforestry systems alters SOC biological and thermal stabilities, and these agroforestry systems have the added bonus effect of sequestering stable SOC in the context of climate change, and thus, maintaining the hedgerow system and expansion of agroforestry systems, may enhance C stability, promote C sequestration and climate change mitigation