Age of soil organic matter and soil respiration: Radiocarbon constraints on belowground C dynamics

  • Wang H
  • Wang Y
  • Amundson R
 et al. 
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Soil organic matter OM) can be stabilized against decomposition by association with minerals, by its inherent recalcitrance and by occlusion in aggregates. However, the relative contribution of these factors to OM stabilization is yet unknown. We analyzed pool size and isotopic composition (C-14, C-13) of mineral-protected and recalcitrant OM in 12 subsurface horizons from 10 acidic forest soils. The results were related to properties of the mineral phase and to OM composition as revealed by CPMAS C-13- NMR and CuO oxidation. Stable OM was defined as that material which survived treatment of soils with 6 wt% sodium hypochlorite (NaOCl). Mineral-protected OM was extracted by subsequent dissolution of minerals by 10% hydrofluoric acid HF). Organic matter resistant against NaOCl and insoluble in HF was considered as recalcitrant OM. Hypochlorite removed primarily C-14-modern OM. Of the stable organic carbon (OC), amounting to 2.4-20.6 g kg(-1) soil, mineral dissolution released on average 73%. Poorly crystalline Fe and Al phases (Fe-o, Al-o) and crystalline Fe oxides (Fed-o) explained 86% of the variability of mineral-protected OC. Atomic C-p/( Fe+ Al)(p) ratios of 1.3 - 6.5 suggest that a portion of stable OM was associated with polymeric Fe and Al species. Recalcitrant OC (0.4 - 6.5 g kg(-1) soil) contributed on average 27% to stable OC and the amount was not correlated with any mineralogical property. Recalcitrant OC had lower Delta(14)C and delta(13)C values than mineral-protected OC and was mainly composed of aliphatic (56%) and O-alkyl (13%) C moieties. Lignin phenols were only present in small amounts in either mineral-protected or recalcitrant OM mean 4.3 and 0.2 g kg(-1) OC). The results con. rm that stabilization of OM by interaction with poorly crystalline minerals and polymeric metal species is the most important mechanism for preservation of OM in these acid subsoil horizons.

Author-supplied keywords

  • 13 may 2001
  • 14C activity
  • 14c
  • 22 june 2001
  • 28 february 2001 acceptance
  • AMS
  • Aggregate
  • Belowground processes and global change
  • C isotopes
  • Carbon allocation
  • Carbon contort extrapolations
  • Carbon cycle
  • Carbon stabilization
  • Chemical composition
  • Compound specific radiocarbon
  • Deep soil
  • Depth profiles
  • Ecosystem allocation
  • Fagus silvativa
  • Fagus sylvatica
  • Fine root production
  • Fine root turnover
  • Fractionation
  • Global climate change
  • Hydrofluoric acid
  • Isotopes
  • Lignin
  • Microscopy
  • Molecular analysis
  • New AMS facility
  • Nuclear magnetic resonance spectroscopy
  • Organic matter
  • Particle
  • Picea abies
  • Plant functional types
  • Plant-climate interactions
  • Polysaccharides
  • Precipitation reduction
  • Process blank
  • Radiocarbon
  • Radiocarbon sample preparation
  • Recalcitrant organic matter
  • Root : shoot ratio
  • Root area index
  • Root distributions
  • Root morphology
  • Sandy soils
  • Sink
  • Small samples
  • Sodium hypochlorite
  • Soil carbon stabilization
  • Soil carbon storage
  • Soil gradients
  • Soil organic matter
  • Soil respiration
  • Soil water storage capacity
  • Soil-climate-vegetation relationships
  • Source
  • Spectroscopy
  • Stabilisation
  • Stable organic matter
  • Subsoil
  • Turnover rate
  • Visualization
  • carbon cycle
  • climate
  • copyright
  • data analysis
  • education
  • fine roots
  • palaeontological association
  • radiocarbon
  • root density
  • software
  • soil organic matter
  • state factor
  • submission

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  • H Wang

  • Yang Wang

  • Ronald Amundson

  • Susan Trumbore

  • E. D. Vance

  • P. C. Brookes

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