Influence of stand composition on soil organic carbon stabilization and biochemistry in aspen and conifer forests of Utah

Abstract

To assess the potential impact of conifer encroachment on soil organic carbon (SOC) dynamics and storage in montane aspen-conifer forests from the interior western US, we sampled mineral soils (0–15 cm) across the aspen-conifer ecotones in southern and northern Utah and quantified total SOC stocks, stable SOC (i.e., mineral-associated SOC (MoM)), labile SOC (i.e., light fraction (LF), decomposable (CO2 release during long-term aerobic incubations) and soluble SOC (hot water extractable organic carbon (HWEOC)). Total SOC storage (47.0 ± 16.5 Mg C ha −1 ) and labile SOC as LF (14.0 ± 7.10 Mg C ha −1 ), SOC decomposability (cumulative released CO2-C of 5.6 ± 3.8 g C g −1 soil) or HWEOC (0.6 ± 0.6 mg C g −1 soil) did not differ substantially with vegetation type, although a slight increase in HWEOC was observed with increasing conifer in the overstory. There were statistically significant differences (p = 0.035) in stable MoM storage, which was higher under aspen (31.2 ± 15.1 Mg C ha −1 ) than under conifer (22.8 ± 9.0 Mg C ha -1 ), with intermediate values under mixed (25.7 ± 8.8 Mg C ha -1 ). Texture had the greatest impact on SOC distribution among labile and stable fractions, with increasing stabilization in MoM and decreasing bio-availability of SOC with increasing silt + clay content. Only at lower silt + clay contents (40%–70%) could we discern the 1 Coauthored by Mercedes Roman Dobarco and Helga Van Miegroet. Published in the journal Forests 2014, 5(4), 666-688; doi:10.3390/f5040666 33 influence of vegetation on MoM content. This highlights the importance of chemical protection mechanisms for long-term C sequestration.