Aggregate-associated soil organic matter as an ecosystem property and a measurement tool ☆

Abstract Our 2000 paper Soil macroaggregate turnover and microaggregate formation: A mechanism for C sequestration under no-tillage agriculture had its genesis in attempts to identify and isolate soil organic matter (SOM) fractions that reflect the impacts of climate, soil physiochemical properties and physical disturbance on the soil organic carbon balance. A key prerequisite for the investigation was the development of a simple device to isolate the microaggregates (53–250 μm) contained within stable (i.e., resistant to slaking) macroaggregates (>250 μm) obtained by conventional wet-sieving. By comparing the abundance and C content of micro-within-macroaggregates, the size distribution of intra-aggregate particulate organic matter (iPOM) and isotopically-based estimates of the age of the organic matter in the different fractions, we were able to corroborate our hypothesis that the absence of tillage (i.e., in no-till and native soils) promotes greater longevity of newly-formed macroaggregates, resulting in greater SOM stabilization in microaggregates formed within stable macroaggregates. Follow-up research has indicated that the microaggregate-within-macroaggregate fraction is 1) potentially a robust indicator for management-induced SOC changes over decadal time scales, 2) of biological origin and therefore useful in interpreting impacts of soil biota on soil C and N dynamics, but not in-situ CO 2 and N 2 O fluxes, 3) useful in complimentary chemical and spectroscopic approaches to relate SOM dynamics to soil structure and attributes of the soil pore space, and 4) a good candidate for being incorporated into models as a measurable fraction.

[1]  B. D. Kay,et al.  Rates of Change of Soil Structure Under Different Cropping Systems , 1990 .

[2]  J. Six,et al.  Microbial community assimilation of cover crop rhizodeposition within soil microenvironments in alternative and conventional cropping systems , 2012, Plant and Soil.

[3]  Rattan Lal,et al.  Carbon sequestration in soils , 1999 .

[4]  J. Six,et al.  Microbial community composition and carbon cycling within soil microenvironments of conventional, low-input, and organic cropping systems. , 2011, Soil biology & biochemistry.

[5]  Anthony R. Dexter,et al.  Advances in characterization of soil structure , 1988 .

[6]  J. Six,et al.  Microaggregate-associated carbon as a diagnostic fraction for management-induced changes in soil organic carbon in two Oxisols , 2007 .

[7]  J. Six,et al.  Indications for Soil Carbon Saturation in a Temperate Agroecosystem , 2008 .

[8]  E. T. Elliott,et al.  Physical separation of soil organic matter , 1991 .

[9]  Johan Six,et al.  Aggregation and soil organic matter accumulation in cultivated and native grassland soils , 1998 .

[10]  Johan Six,et al.  Soil macroaggregate turnover and microaggregate formation: a mechanism for C sequestration under no-tillage agriculture , 2000 .

[11]  K. Paustian,et al.  A re‐evaluation of the enriched labile soil organic matter fraction , 2000 .

[12]  J. Marinissen,et al.  Soil structure and earthworm activity in a marine silt loam under pasture versus arable land , 2001, Biology and Fertility of Soils.

[13]  E. T. Elliott.  Aggregate structure and carbon, nitrogen, and phosphorus in native and cultivated soils , 1986 .

[14]  K. Paustian,et al.  Soil Aggregation and Soil Organic Carbon Stabilization: Effects of Management in Semiarid Mediterranean Agroecosystems , 2009 .

[15]  J. Skjemstad,et al.  Structural and dynamic properties of soil organic-matter as reflected by 13C natural-abundance, pyrolysis mass-spectrometry and solid-state 13C NMR-spectroscopy in density fractions of an oxisol under forest and pasture , 1995 .

[16]  E. T. Elliott,et al.  Particulate soil organic-matter changes across a grassland cultivation sequence , 1992 .

[17]  D. Coleman,et al.  Let the soil work for us , 1988 .

[18]  R. Kachanoski,et al.  Carbon mineralization in soil size fractions after various amounts of aggregate disruption , 1989 .

[19]  E. T. Elliott,et al.  Carbon and Nitrogen Distribution in Aggregates from Cultivated and Native Grassland Soils , 1993 .

[20]  J. Six,et al.  Pore structure changes during decomposition of fresh residue: X-ray tomography analyses , 2006 .

[21]  R. Protz,et al.  Chemistry and micromorphology of aggregation in earthworm casts , 1989 .

[22]  J. Tisdall,et al.  Organic matter and water‐stable aggregates in soils , 1982 .

[23]  J. Six,et al.  Preferential accumulation of microbial carbon in aggregate structures of no-tillage soils , 2004 .

[24]  W. Post,et al.  AggModel: A soil organic matter model with measurable pools for use in incubation studies , 2013 .

[25]  P. Sale,et al.  The influence of the soil matrix on nitrogen mineralisation and nitrification V. Microporosity and manganese , 1999 .

[26]  P. Sale,et al.  The influence of the soil matrix on nitrogen mineralisation and nitrification. IV.Texture , 1999 .

[27]  Julie D. Jastrow,et al.  Soil aggregate formation and the accrual of particulate and mineral-associated organic matter , 1996 .

[28]  K. Paustian,et al.  Sources and composition of soil organic matter fractions between and within soil aggregates , 2001 .

[29]  Johan Six,et al.  Carbon Sequestration in Microaggregates of No‐Tillage Soils with Different Clay Mineralogy , 2004 .

[30]  E. T. Elliott,et al.  Methods for physical separation and characterization of soil organic matter fractions , 1993 .

[31]  I. Kögel‐Knabner,et al.  Content and composition of free and occluded particulate organic matter in a differently textured arable Cambisol as revealed by solid‐state 13C NMR spectroscopy , 2004 .

[32]  P. Lavelle,et al.  Transformation of the soil structure through Pontoscolex corethrurus (Oligochaeta) intestinal tract , 1993 .

[33]  P. Sale,et al.  The influence of the soil matrix on nitrogen mineralisation and nitrification III. Predictive utility of traditional variables and process location within the pore system , 1999 .

[34]  K. Paustian,et al.  Modeling the Measurable or Measuring the Modelable: A Hierarchical Approach to Isolating Meaningful Soil Organic Matter Fractionations , 1996 .

[35]  J. Six,et al.  Impacts of different N management regimes on nitrifier and denitrifier communities and N cycling in soil microenvironments. , 2010, Soil biology & biochemistry.

[36]  E. T. Elliott,et al.  Carbon and Nitrogen Dynamics of Soil Organic Matter Fractions from Cultivated Grassland Soils , 1994 .

[37]  P. Hallett,et al.  Are the links between soil aggregate size class, soil organic matter and respiration rate artefacts of the fractionation procedure? , 2003 .

[38]  J. Six,et al.  Influence of earthworm activity on aggregate-associated carbon and nitrogen dynamics differs with agroecosystem management , 2007 .

[39]  J. Six,et al.  Earthworms and management affect organic matter incorporation and microaggregate formation in agricultural soils , 2005 .

[40]  P. Sale,et al.  The influence of the soil matrix on nitrogen mineralisation and nitrification. II. The pore system as a framework for mapping the organisation of the soil matrix , 1998 .

[41]  Rattan Lal,et al.  Agricultural soils as a sink to mitigate CO2 emissions , 1997 .

[42]  I. Kögel‐Knabner,et al.  Submicron scale imaging of soil organic matter dynamics using NanoSIMS – From single particles to intact aggregates , 2012 .

[43]  J. Crawford,et al.  Spatial distribution of bacterial communities and their relationships with the micro-architecture of soil. , 2003, FEMS microbiology ecology.

[44]  J. Six,et al.  Soil organic matter distribution and microaggregate characteristics as affected by agricultural management and earthworm activity , 2005 .

[45]  R. Protz,et al.  Factors Influencing the Dispersibility of Clay in Worm Casts , 1988 .

[46]  J. Six,et al.  Rapid incorporation of carbon from fresh residues into newly formed stable microaggregates within earthworm casts , 2004 .

[47]  K. Paustian,et al.  Soil structure and organic matter: I. Distribution of aggregate-size classes and aggregate-associated carbon. , 2000 .

[48]  J. Six,et al.  Earthworms, soil fertility and aggregate-associated soil organic matter dynamics in the Quesungual agroforestry system , 2010 .

[49]  Johan Six,et al.  Aggregate and Soil Organic Matter Dynamics under Conventional and No-Tillage Systems , 1999 .

[50]  C. Jacobsen,et al.  Carbon (1s) NEXAFS spectroscopy of biogeochemically relevant reference organic compounds , 2009 .

[51]  Johan Six,et al.  Soil structure and soil organic matter : II. A normalized stability index and the effect of mineralogy , 2000 .

[52]  W. D. Kemper,et al.  Gas displacement and aggregate stability of soils , 1985 .

[53]  R. Bol,et al.  Molecular dynamics of organic matter in a cultivated soil. , 2002 .

[54]  Johan Six,et al.  The relationship between carbon input, aggregation, and soil organic carbon stabilization in sustainable cropping systems , 2005 .

[55]  J. Six,et al.  Protection of soil carbon by microaggregates within earthworm casts , 2005 .

[56]  Rattan Lal,et al.  Managing U.S. cropland to sequester carbon in soil , 1999 .

[57]  K. Ritz,et al.  Tillage, habitat space and function of soil microbes , 2000 .

[58]  J. Crawford,et al.  New methods and models for characterising structural heterogeneity of soil , 2001 .

[59]  D. Coleman,et al.  Habitable pore space and microbial trophic interactions , 1980 .

[60]  C. Cambardella,et al.  Surface residue- and root-derived carbon in stable and unstable aggregates , 2000 .

[61]  J. Six,et al.  Biochemical changes across a carbon saturation gradient: Lignin, cutin, and suberin decomposition and stabilization in fractionated carbon pools , 2012 .