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Mineral Assemblage and Aggregates Control Carbon Dynamics in a California Conifer Forest
Author(s) -
Rasmussen Craig,
Torn Margaret S.,
Southard Randal J.
Publication year - 2005
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2005.0040
Subject(s) - soil water , humus , gibbsite , andesite , vermiculite , mineral , clay minerals , kaolinite , weathering , soil horizon , soil science , mineralogy , chemistry , geology , environmental chemistry , geochemistry , paleontology , organic chemistry , volcano , volcanic rock
Uncertainty about the effects of climate change on terrestrial soil organic 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. Granite and AN soils contained similar clay mineral assemblages as determined by x‐ray diffraction (XRD), dominated by vermiculite, hydroxy‐interlayered vermiculite (HIV), 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. Andesite‐granite 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 14 C measurements, occluded C mean residence time (MRT) > 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 organomineral association with Al‐humus complexes and SRO Al minerals control the variation in soil C dynamics in these systems.