Craig Rasmussen, Univ of Arizona, Soil, Water, and Environmental Science, 520 Shantz Bldg, PO Box 210038, Tucson, AZ 85721
Uncertainty about the effects of climate change on
terrestrial soil organic carbon (C) stocks has generated interest in clarifying
the processes that underlie soil C dynamics.
We investigated the role of soil mineralogy and aggregate stability as
key variables controlling soil C dynamics in a California
conifer forest. We characterized soils
derived from granite (GR) and mixed andesite-granite (AN) parent materials from
similar forest conditions. GR and AN
soils contained similar clay mineral assemblages as determined by X-ray
diffraction (XRD), dominated by vermiculite, hydroxy-interlayered vermiculite,
kaolinite and gibbsite. However, AN soils contained significantly more Al in Al-humus
complexes (6.2 vs. 3.3 kg m-2) and more crystalline and short range
order (SRO) Fe oxyhydroxides (30.6 vs. 16.8 kg m-2) than GR
soils. AN
pedons contained nearly 50% more C relative to GR soils (22.8 vs. 15.0 kg m-2). Distribution of C within density and
aggregate fractions (free, occluded, and mineral associated C) varied
significantly between AN and GR soils. In particular, AN
soils had at least twice as much mineral associated C relative to GR soils in
all horizons. Based on 14C
measurements, occluded C mean residence time > mineral C > free C in both
soil types, suggesting a significant role for aggregate C protection in
controlling soil C turnover. We found
highly significant, positive correlations between Al-humus complexes, SRO Al
minerals and total C content. We suggest
that a combination of aggregate protection and organo-mineral association with
Al-humus complexes and SRO Al minerals control the variation in soil C dynamics
in these systems.
Back to Symposium--Mineralogical Regulation of Soil Carbon Storage
Back to S09 Soil Mineralogy
Back to The ASA-CSSA-SSSA International Annual Meetings (November 12-16, 2006)