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Processes of Soil Organic‐Matter Accretion at a Mudfloe Chronosequence, Mt. Shasta, California
Author(s) -
Sollins P.,
Spycher G.,
Topik C.
Publication year - 1983
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1937835
Subject(s) - organic matter , chronosequence , soil organic matter , soil water , soil science , chemistry , geology , environmental science , mineralogy , environmental chemistry , hydrology (agriculture) , organic chemistry , geotechnical engineering
Amounts of carbon and nitrogen were measured in bulk soils and compenent density fractions from four mudflows (A, B, D, E) of increasing age at Mt. Shasta, California, in order to gain insight into mechanisms of soil organic—matter accretion. Soil was divided into a light fraction (specific gravity < 1.65 g/cm 3 ) in which organic matter consisted mainly of root fragments and other plant remnants and a heavy fraction in which most of the organic matter was adsorbed on mineral surfaces and occluded within organomineral microaggregates. In bulk soil and the heavy fraction, amounts of C and N increased consistently with flow age and were even greater at an older, mineralogically similar site previously studied in the Oregon Cascade Range. Amounts of light—fraction C and N increased from flow A to D but were lower at flow E. Regardless of soil age, the heavy fraction contained 55—88% of the total soil N and 37—72% of the total soil C. Thus, the heavy fraction is the major long—term sink for N and an important sink for C. Soil properties and vegetation were exceptionally variable at the D and E flows. A multiple regression on rockiness of the soil (volume of fragments > 2mm) and a tree index (reflecting number and size of trees near each soil—sampling point and their proximity) accounted for 50—80% of the variability in light—fraction C and N at the D and E flows but not at the A and B flows, where all parameters were less variable. Rockiness and tree index accounted for little of the variability in heavy—fraction C and N, indicating that light— and heavy—fraction organic—matter accumulate in response to different factors. It appears that mass and composition of light—fraction organic matter correlate with short—term changes in biological activity, whereas heavy—fraction organic matter accumulates steadily and correlates with long—term processes such as mineral weathering and soil horizon formation.