Storage and Stability of Soil Organic Carbon in Aspen and Conifer Forest Soils of Northern Utah

Abstract

This study compares the amount, distribution, and stability of soil organic carbon (SOC) in six paired quaking aspen (Populus tremuloides Michx) and conifer plots at three locations in northern Utah, to assess the influence of vegetation cover and other biotic and abiotic drivers on SOC storage capacity in seasonally dry environments. Aspen soils accumulated significantly more SOC in the mineral soil (0–60 cm) (92.2 ± 26.7 Mg C ha−1 vs. 66.9 ± 18.6 Mg C ha−1 under conifers), and despite thicker O horizons under conifers that contained higher amounts of SOC (11.6 ± 8.8 Mg C ha−1 under conifers vs. 1.65 ± 0.38 Mg C ha−1 in aspen), across all sites SOC storage was 25% higher under aspen. Shallow soil cores (0–15 cm) did not indicate significant differences in SOC with vegetation type. The SOC under aspen was also more stable, indicated by well‐developed mollic epipedon (A horizon 38–53‐cm thick vs. 5.5–34 cm under conifers), slower turnover of surficial SOC deduced from long‐term laboratory incubations (67.7 ± 15.7 g CO2–C per kg C for aspen vs. 130.9 ± 41.3 g CO2–C per kg C for conifer soils), and a greater preponderance of mineral‐associated SOC (55±13% in aspen vs. 41±13% in conifer). Aspen soils were generally wetter and we hypothesize that rapid litter turnover coupled with greater water supply may have caused greater downward redistribution and adsorption of dissolved organic carbon (DOC) in aspen soils.