Application of eddy covariance measurements to the temperature dependence of soil organic matter mean residence time

Abstract. We have set up a facility allowing steady state 13CO2 labeling of short stature vegetation (12 m2) for several years. 13C labelling is obtained by scrubbing the CO2 from outdoors air with a self-regenerating molecular sieve and by replacing it with 13C depleted (−34.7±0.03‰) fossil-fuel derived CO2 The facility, which comprises 16 replicate mesocosms, allows to trace the fate of photosynthetic carbon in plant-soil systems in natural light and at outdoors temperature. This method was applied to the study of soil organic carbon turnover in temperate grasslands. We tested the hypothesis that a low disturbance by grazing and cutting of the grassland increases the mean residence time of carbon in coarse (>0.2 mm) soil organic fractions. Grassland monoliths (0.5×0.5×0.4 m) were sampled from high and low disturbance treatments in a long-term (14 yrs) grazing experiment and were placed during two years in the mesocosms. During daytime, the canopy enclosure in each mesocosm was supplied in an open flow with air at mean CO2 concentration of 425 µmol mol−1 and δ13C of −21.5±0.27‰. Fully labelled mature grass leaves reached a δ13C of −40.8 (±0.93) and −42.2‰ (±0.60) in the low and high disturbance treatments, respectively, indicating a mean 13C labelling intensity of 12.7‰ compared to unlabelled control grass leaves. After two years, the delta 13C value of total soil organic matter above 0.2 mm was reduced in average by 7.8‰ in the labelled monoliths compared to controls. The isotope mass balance technique was used to calculate for the top (0–10 cm) soil the fraction of 13C labelled carbon in the soil organic matter above 0.2 mm (i.e. roots, rhizomes and particulate organic matter). A first order exponential decay model fitted to the unlabelled C in this fraction shows an increase in mean residence time from 22 to 31 months at low compared to high disturbance. A slower decay of roots, rhizomes and particulate organic matter above 0.2 mm is therefore likely to contribute to the observed increased in soil carbon sequestration in grassland monoliths exposed to low disturbance.

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Age, turnover and molecular diversity of soil organic matter in aggregates of a Gleysol

Canadian Journal of Soil Science ◽

10.4141/s95-064 ◽

1997 ◽

Vol 77 (3) ◽

pp. 379-388 ◽

Cited By ~ 61

Author(s):

C. M. Monreal ◽

H.-R. Schulten ◽

H. Kodama

Keyword(s):

Mass Spectrometry ◽

Fatty Acids ◽

Organic Matter ◽

Soil Organic Matter ◽

Residence Time ◽

Mean Residence Time ◽

Turnover Time ◽

Ionization Mass ◽

Organic C ◽

Soil Organic Matter Turnover

We used an integrated approach to describe soil organic matter (SOM) dynamics through known inorganic and organic components in aggregates of adjacent forested and cultivated Gleysolic soil. Mineral and SOM components were examined in water stable macroaggregates (>250 µm), microaggregates 1 (50–250 µm) and microaggregates 2 (<50 µm) fractions. SOM was characterized by pyrolysis-field ionization mass spectrometry (Py-FIMS), and soil minerals by X-ray diffraction analysis. The mean residence time of organic-C (OC) was determined using radiocarbon dating. OC turnover was determined using the natural abundance of native 13C and that derived from corn residue. We found that OC in macroaggregates was young (<100 yr), turned over in 14 yr, and consisted of OM typical of that found in tissues of plants and soil organisms. Chemical classes of compounds in macroaggregates consisted mainly of carbohydrates, lignin monomers and phenols, lignin dimers, lipids (alkanes, alkenes, n-alkyl esters), fatty acids, sterols, suberin and aliphatic and aromatic N compounds. The fast turnover time of OC in larger size aggregates supports the hypothesis that the initial decline in SOM after breaking native land is associated with losses of SOM stored in macroaggregates. OC in microaggregates 1 was young (<100 yr) and turned over in 61 yr. OC in microaggregates 2 was old, turned over in 275 yr, and consisted of highly humified macromolecules. Pyrolyzable SOM products representing plant and microbial components like lignin dimers, sterols, suberin and fatty acids were absent from microaggregates 2 containing old OC. The turnover time of OC correlated directly with the amount of smectite and Al extracted with ammonium oxalate, inversely with non-expandable phyllosilicates, and weakly with the total clay content of aggregates. Thermolabile and thermostable molecular components in aggregates indicated degree of association between SOM and clay minerals. Carbohydrates, peptides and alkylaromatics appeared to be less affected by abiotic stabilization reactions. Key words: Soil organic matter, turnover, mean residence time, inorganic soil components, mass spectrometry, macroaggregates and microaggregates

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Carbon and nitrogen molecular composition of soil organic matter fractions resistant to oxidation

Soil Research ◽

10.1071/sr16182 ◽

2017 ◽

Vol 55 (8) ◽

pp. 809

Author(s):

Katherine Heckman ◽

Dorisel Torres ◽

Christopher Swanston ◽

Johannes Lehmann

Keyword(s):

Molecular Structure ◽

Organic Matter ◽

Soil Organic Matter ◽

Residence Time ◽

Mean Residence Time ◽

Chromic Acid ◽

Soil Morphology ◽

Fuel Type ◽

Organic Residues ◽

Photo Oxidation

The methods used to isolate and characterise pyrogenic organic carbon (PyC) from soils vary widely, and there is little agreement in the literature as to which method truly isolates the most chemically recalcitrant (inferred from oxidative resistance) and persistent (inferred from radiocarbon abundance) fraction of soil organic matter. In addition, the roles of fire, fuel type and soil morphology in the preservation of PyC are not yet defined. In an attempt to elucidate the importance of oxidative recalcitrance, fuel type and soil morphology to the persistence of soil organic matter, we examined two strongly contrasting soils using a variety of PyC isolation techniques coupled with quantifications of the molecular structure and mean residence time of the isolated organic materials. Surface and subsurface soil samples were examined from a Red Chromosol soil and a Black Vertosol soil. The δ13C values suggest that PyC in the Red Chromosol was sourced from eucalyptus, whereas PyC in the Black Vertosol was formed from grass. Soils were sieved at 53µm, treated with hydrofluoric acid to remove organics associated with mineral surfaces, then subjected to three common ‘PyC isolation’ treatments: chromic acid, photo-oxidation and chromic acid followed by photo-oxidation. Molecular structure of the organic residues remaining after each treatment was quantified by solid-state 13C cross polarisation magic angle spinning nuclear magnetic resonance and near edge X-ray absorption fine structure spectroscopy, and the mean residence time of the organic residues was estimated based on radiocarbon abundance. In all cases, treatment with chromic acid followed by photo-oxidation isolated the smallest proportion of organic matter (5–10% of <53µm C) which also had the longest mean residence time (estimated 600–3460 years). Additionally, molecular structure measurements indicated that this fraction was not composed solely of aromatic compounds, suggesting a non-homogenous source for the most oxidative-resistant fraction of soil organic matter.

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Mean residence time of soil organic matter associated with kaolinite and smectite

European Journal of Soil Science ◽

10.1046/j.1365-2389.2003.00512.x ◽

2003 ◽

Vol 54 (2) ◽

pp. 269-278 ◽

Cited By ~ 108

Author(s):

E. J. W. Wattel- Koekkoek ◽

P. Buurman ◽

J. Van Der Plicht ◽

E. Wattel ◽

N. Van Breemen

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Residence Time ◽

Mean Residence Time

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Reactivation of nutrient cycling in an urban tropical dry forest after abandonment of agricultural activities

REVISTA CHAPINGO SERIE CIENCIAS FORESTALES Y DEL AMBIENTE ◽

10.5154/r.rchscfa.2020.11.068 ◽

2021 ◽

Vol 27 (3) ◽

pp. 355-365

Author(s):

Juan D. León-Peláez ◽

◽

William Caicedo-Ruiz ◽

Jeiner Castellanos-Barliza ◽

◽

...

Keyword(s):

Organic Matter ◽

Leaf Litter ◽

Residence Time ◽

Mean Residence Time ◽

Dry Forest ◽

Agricultural Activities ◽

Forest Fragment ◽

Leaf Litterfall ◽

Passive Restoration ◽

Standing Litter

Introduction: Standing leaf litter represent an essential source of organic matter and nutrients to dynamize biogeochemical processes at the ecosystem level. Objectives: To characterize the accumulation and decomposition of organic materials and flow of nutrients from standing litter in an urban dry tropical forest in a successional stage, after 10 years of abandonment of agricultural activities, and to determine the potential use of three species in future active restoration activities. Materials and methods: Standing litter samples were collected from a forest fragment in Santa Marta, Colombia, separating leaves, reproductive material, woody material and other residues. Additionally, leaves of three species of interest for ecological restoration (Albizia niopoides Spruce ex Benth., Cordia alba [Jacq.] Roem. & Schult. and Machaerium milleflorum Dugand G. A.) were separated and Ca, Mg, K, N and P concentrations were determined. Results and discussion: Total standing litter was 8.3 Mg∙ha-1 with a mean residence time of two years. The leaves represented 20% of the standing litter, with a mean residence time of 1.4 years. Based on the decomposition constant (kj = 0.73) and the rate of leaf litterfall, organic matter returns accounted for 3.4 Mg∙ha-1∙year-1. Leaf decomposition rate decreased in the following order C. alba > M. milleflorum > A. niopoides. P represented the greatest limitation with low release rates (0.1 to 1.2 kg∙ha-1∙year-1). Conclusions: The passive restoration strategy allowed reactivation of biogeochemical cycle via fine leaf litter. Cordia alba showed potential for inclusion in restoration activities, with lower values for leaf N/P ratio, and higher rates for leaf litterfall, litter decomposition and nutrient release.

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Radiocarbon Variation in Charcoal/Wood and Soil Fractions from a Loessic Setting in Central Alaska

Radiocarbon ◽

10.1017/rdc.2016.41 ◽

2016 ◽

Vol 59 (2) ◽

pp. 449-464 ◽

Cited By ~ 1

Author(s):

Joshua D Reuther ◽

Alexander Cherkinsky ◽

Sam Coffman

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Residence Time ◽

Age Differences ◽

Soil Formation ◽

Soil Samples ◽

Small Particles ◽

Vegetation Development ◽

Lucky Strike ◽

Soil Residue

AbstractThe Healy’s Lucky Strike site in central Alaska has an exceptional Holocene loess-paleosol sequence that has afforded us the ability to look at variation in 14C dating of soil organic matter (SOM) fractions in a high-latitude loess setting. Our work has focused on comparing the radiocarbon ages of charcoal and wood to base-soluble humic acids (HA) and base-insoluble soil residue (SR) fractions from bulk soil samples. Charcoal/wood ages were younger than HA ages reflecting the later stages of vegetation development at the surface of the soils prior to being covered by loess accumulation; the HA ages generally reflect the overall timing of soil formation and mean residence time of SOM. Soil residue ages are older than charcoal/wood and HA ages. SOM ages at this location become increasingly older than charcoal/wood ages with depth, reaching 750 to 8070 yr in difference and associated with weakly developed soils at the lowest depths. We suggest the drastic SOM age differences at this site result from the differential incorporation of small particles of coal throughout the sedimentary matrices introduced older contaminants to SR fractions.

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