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Turnover and storage of C and N in five density fractions from California annual grassland surface soils
Author(s) -
Baisden W. T.,
Amundson R.,
Cook A. C.,
Brenner D. L.
Publication year - 2002
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2001gb001822
Subject(s) - soil water , chronosequence , decomposition , organic matter , soil organic matter , environmental chemistry , mineral , grassland , environmental science , chemistry , mineralogy , soil science , geology , agronomy , biology , organic chemistry
We measured 14 C/ 12 C in density fractions from soils collected before and after atmospheric thermonuclear weapons testing to examine soil organic matter (SOM) dynamics along a 3 million year California soil chronosequence. The mineral‐free particulate organic matter (FPOM; <1.6 g cm −3 ) mainly contains recognizable plant material, fungal hyphae, and charcoal. Mineral‐associated light fractions (1.6–2.2 g cm −3 ) display partially or completely humified fine POM, while the dense fraction (>2.2 g cm −3 ) consists of relatively OM‐free sand and OM‐rich clays. Three indicators of decomposition (C:N, δ 13 C, and δ 15 N) all suggest increasing SOM decomposition with increasing fraction density. The Δ 14 C‐derived SOM turnover rates suggest that ≥90% of FPOM turns over in <10 years. The four mineral‐associated fractions contain 69–86% “stabilized” (decadal) SOM with the remainder assumed to be “passive” (millenial) SOM. Within each soil, the four mineral‐associated fractions display approximately the same residence time (34–42 years in 200 kyr soil, 29–37 years in 600 kyr soil, and 18–26 years in 1–3 Myr soils), indicating that a single stabilized SOM “pool” exists in these soils and may turn over primarily as a result of soil disruption.