The dynamics of organic matter in rock fragments in soil investigated by 14C dating and measurements of 13C

Rock fragments in soil can contain significant amounts of organic carbon. We investigated the nature and dynamics of organic matter in rock fragments in the upper horizons of a forest soil derived from sandstone and compared them with the fine earth fraction (<2 mm). The organic C content and its distribution among humic, humin and non‐humic fractions, as well as the isotopic signatures (Δ14C and δ13C) of organic carbon and of CO2 produced during incubation of samples, all show that altered rock fragments contain a dynamic component of the carbon cycle. Rock fragments, especially the highly altered ones, contributed 4.5% to the total organic C content in the soil. The bulk organic matter in both fine earth and highly altered rock fragments in the A1 horizon contained significant amounts of recent C (bomb 14C), indicating that most of this C is cycled quickly in both fractions. In the A horizons, the mean residence times of humic substances from highly altered rock fragments were shorter than those of the humic substances isolated in the fine earth. Values of Δ14C of the CO2 produced during basal respiration confirmed the heterogeneity, complexity and dynamic nature of the organic matter of these rock fragments. The weak 14C signatures of humic substances from the slightly altered rock fragments confirmed the importance of weathering in establishing and improving the interactions between rock fragments and surrounding soil. The progressive enrichment in 13C from components with high‐14C (more recent) to low‐14C (older) indicated that biological activity occurred in both the fine and the coarse fractions. Hence the microflora utilizes energy sources contained in all the soil compartments, and rock fragments are chemically and biologically active in soil, where they form a continuum with the fine earth.

[1]  A. Agnelli,et al.  Microbial biomass-C and basal respiration of fine earth and highly altered rock fragments of two forest soils , 2001 .

[2]  P. Puget,et al.  Dynamics of soil organic matter associated with particle‐size fractions of water‐stable aggregates , 2000 .

[3]  K. Kalbitz,et al.  Land use impacts on the isotopic signature (13C, 14C, 15N) of water-soluble fulvic acids in a German fen area , 2000 .

[4]  Susan E. Trumbore,et al.  AGE OF SOIL ORGANIC MATTER AND SOIL RESPIRATION: RADIOCARBON CONSTRAINTS ON BELOWGROUND C DYNAMICS , 2000 .

[5]  A. Agnelli,et al.  Chemical and spectroscopic characterization of the humic substances from sandstone-derived rock fragments , 2000 .

[6]  G. Eglinton,et al.  Radiocarbon Dating of Aliphatic Hydrocarbons A New Approach for Dating Passive-Fraction Carbon in Soil Horizons , 1999 .

[7]  R. Bol,et al.  The influence of soil processes on carbon isotope distribution and turnover in the British uplands , 1999 .

[8]  A. Agnelli,et al.  Classing the soil skeleton (greater than two millimeters) : Proposed approach and procedure , 1998 .

[9]  S. Archer,et al.  δ13C values of soil organic carbon and their use in documenting vegetation change in a subtropical savanna ecosystem , 1998 .

[10]  Steven W. Leavit.  Biogeochemistry, An Analysis of Global Change , 1998 .

[11]  S. Trumbore,et al.  Potential responses of soil organic carbon to global environmental change. , 1997, Proceedings of the National Academy of Sciences of the United States of America.

[12]  Gary A. Peterson,et al.  Radiocarbon Dating for Determination of Soil Organic Matter Pool Sizes and Dynamics , 1997 .

[13]  Gary A. Peterson,et al.  Carbon isotope ratios of great plains soils and in wheat-fallow systems , 1997 .

[14]  A. Agnelli,et al.  Mineralogical, physical, and chemical properties of rock fragments in soil , 1996 .

[15]  G. Eglinton,et al.  The 14C age and residence time of organic matter and its lipid constituents in a stagnohumic gley soil , 1996 .

[16]  N. Batjes,et al.  Total carbon and nitrogen in the soils of the world , 1996 .

[17]  R. Amundson,et al.  Rapid Exchange Between Soil Carbon and Atmospheric Carbon Dioxide Driven by Temperature Change , 1996, Science.

[18]  P. Vitousek,et al.  Soil organic matter dynamics along gradients in temperature and land use on the Island of Hawaii , 1995 .

[19]  S. Trumbore.  Comparison of carbon dynamics in tropical and temperate soils using radiocarbon measurements , 1993 .

[20]  H. Neue,et al.  Bomb-carbon, 14C-dating and 13C-measurements as tracers of organic matter dynamics as well as of morphogenetic and turbation processes , 1989 .

[21]  R. Hodson,et al.  Depletion of 13C in lignin and its implications for stable carbon isotope studies , 1987, Nature.

[22]  C. D. Kimpe,et al.  PROPRIETES DE QUELQUES SOLS RICHES EN GRAVIERS DANS LA REGION DE QUEBEC , 1980 .

[23]  D. Buchanan,et al.  Sealed Tube Combustions for Determination of Carbon- 14 and Total Carbon , 1959 .

[24]  E. Teller,et al.  ADSORPTION OF GASES IN MULTIMOLECULAR LAYERS , 1938 .

[25]  Eric A. Davidson,et al.  Soil carbon cycling in a temperate forest: radiocarbon-based estimates of residence times, sequestration rates and partitioning of fluxes , 2000 .

[26]  I. Levin,et al.  RADIOCARBON - A UNIQUE TRACER OF GLOBAL CARBON CYCLE DYNAMICS , 2000 .

[27]  J. Deckers,et al.  World Reference Base for Soil Resources , 1998 .

[28]  T. Boutton,et al.  Stable carbon isotope ratios of soil organic matter and their use as indicators of vegetation and climate change. , 1996 .

[29]  S. Trumbore,et al.  Applications of accelerator mass spectrometry to soil science. , 1996 .

[30]  Hari Eswaran,et al.  Organic Carbon in Soils of the World , 1993 .

[31]  J. Vogel.  Rapid Production of Graphite Without Contamination for Biomedical AMS , 1992, Radiocarbon.

[32]  André Mariotti,et al.  Natural 13C abundance as a tracer for studies of soil organic matter dynamics , 1987 .

[33]  F. J. Stevenson.  HUmus Chemistry Genesis, Composition, Reactions , 1982 .

[34]  B. J. O'brien,et al.  Movement and turnover of soil organic matter as indicated by carbon isotope measurements , 1978 .

[35]  M. Stuiver,et al.  Discussion Reporting of 14C Data , 1977, Radiocarbon.