Comparison of Fractionation Methods for Soil Organic Matter <sup>14</sup>C Analysis

Trumbore, Susan E.; Zheng, Shuhui

doi:10.1017/s0033822200017598

Cited by 165 publications

(137 citation statements)

References 40 publications

Supporting

Mentioning

126

Contrasting

Unclassified

Order By: Relevance

“…Thus, a heterogeneous mixture of organic components in SOM is reflected by a wide range in 14 C ages from recent, including post-1954 ("bomb") material with absurd 14 C ages of up to more than 20,000 y (Scharpenseel and Becker-Heidmann, 1992;Trumbore and Zheng, 1996).…”

Section: Carbon-14 Analysis Of Sommentioning

confidence: 99%

“…In modern soils, this interpretation is problematical because of the presence of bomb-14 C. (2) Bomb-14 C, derived from atmospheric testing of nuclear weapons, mainly in the late 1950s until the early 1960s, can be used as a tracer for C exchanges that occurred on decadal time scales (Trumbore and Zheng, 1996). However, this approach requires the availability of archived soil samples collected before the release of bomb-14 C into the atmosphere, to correct the measured bomb-14 C contributions for the effect of aging of SOM.…”

Section: Carbon-14 Analysis Of Sommentioning

confidence: 99%

See 1 more Smart Citation

How relevant is recalcitrance for the stabilization of organic matter in soils?

Marschner

Brodowski

Dreves

et al. 2008

Z. Pflanzenernähr. Bodenk.

625

359

View full text Add to dashboard Cite

Traditionally, the selective preservation of certain recalcitrant organic compounds and the formation of recalcitrant humic substances have been regarded as an important mechanism for soil organic matter (SOM) stabilization. Based on a critical overview of available methods and on results from a cooperative research program, this paper evaluates how relevant recalcitrance is for the long-term stabilization of SOM or its fractions. Methodologically, recalcitrance is difficult to assess, since the persistence of certain SOM fractions or specific compounds may also be caused by other stabilization mechanisms, such as physical protection or chemical interactions with mineral surfaces. If only free particulate SOM obtained from density fractionation is considered, it rarely reaches ages exceeding 50 y. Older light particles have often been identified as charred plant residues or as fossil C. The degradability of the readily bioavailable dissolved or water-extractable OM fraction is often negatively correlated with its content in aromatic compounds, which therefore has been associated with recalcitrance. But in subsoils, dissolved organic matter aromaticity and biodegradability both are very low, indicating that other factors or compounds limit its degradation. Among the investigated specific compounds, lignin, lipids, and their derivatives have mean turnover times faster or similar as that of bulk SOM. Only a small fraction of the lignin inputs seems to persist in soils and is mainly found in the fine textural size fraction (<20 lm), indicating physico-chemical stabilization. Compound-specific analysis of 13 C : 12 C ratios of SOM pyrolysis products in soils with C3-C4 crop changes revealed no compounds with mean residence times of > 40-50 y, unless fossil C was present in substantial amounts, as at a site exposed to lignite inputs in the past. Here, turnover of pyrolysis products seemed to be much longer, even for those attributed to carbohydrates or proteins. Apparently, fossil C from lignite coal is also utilized by soil organisms, which is further evidenced by low 14 C concentrations in microbial phospholipid fatty acids from this site. Also, black C from charred plant materials was susceptible to microbial degradation in a short-term (60 d) and a long-term (2 y) incubation

show abstract

Section: Carbon-14 Analysis Of Sommentioning

confidence: 99%

Section: Carbon-14 Analysis Of Sommentioning

confidence: 99%

How relevant is recalcitrance for the stabilization of organic matter in soils?

Marschner

Brodowski

Dreves

et al. 2008

Z. Pflanzenernähr. Bodenk.

625

359

View full text Add to dashboard Cite

show abstract

“…The remaining materials are treated as bulk soils. For soil aggregates fractionation, the > 250 μm and 63-250 μm fractions were isolated by wet sieving [41], and the 2-63 μm and < 2 μm fractions were separated by settling from a suspension [42], the different particle-size aggregate fractions were then freeze-dried and weighed for calculating their relative percentages. Finally the bulk soils and soil aggregate fractions obtained with the above processes were prepared for analysis of the organic carbon (TOC) and total nitrogen (TN) contents, δ 13 C org , δ 15 N, and 14 C.…”

Section: Soil Aggregates Fractionationmentioning

confidence: 99%

“…The soil aggregate fractionation method used in our study has successfully distinguished the differences in SOC turnover times among different particle-size aggregate fractions (Table 4), but failed to yield the active soil organic matter pool with turnover time at the inter-annual scale, thus resulting in an underestimation of the soil CO 2 flux. Therefore, it is necessary to combine the physical fractionation approach with the chemical fractionation or the biological fractionation methods for more effectively separating organic matter into pools that cycle with different intrinsic turnover timescales [35,41,42,116,117]. Such an approach would significantly improve the accuracy of soil CO 2 flux estimates in future studies.…”

Section: Soil Co 2 Fluxmentioning

confidence: 99%

Soil aggregate fraction-based 14C analysis and its application in the study of soil organic carbon turnover under forests of different ages

2013

View full text Add to dashboard Cite

There still exist uncertainties in the trend, magnitude and efficiency of carbon sequestration with regard to the changes in soil organic carbon (SOC) pools after afforestation. In this study, SOC turnover times of the meadow steppe and planted forests at Saihanba Forest Station of Hebei Province, China are estimated by means of the radiocarbon ( 14 C) method. Our results show that the SOC turnover times can be as long as from 70 to 250 years. After planting the Pinus sylvestri var. mongolica in the Leymus chinensis meadow steppe, the turnover times of organic carbon in both bulk samples and soil aggregate fractions of the topsoils are decreased with an increase of the stand age. Such a lowering of the turnover time would cause an increase in soil CO 2 flux, implying that afforestation of grassland may reduce the capacity of topsoil to sequestrate organic carbon. Combined stable isotope and 14 C analyses on soil aggregate fractions suggest that there are different responses to afforestation of grassland between young and old carbon pools in topsoils. In the young and middle-age planted forests, the proportion of CO 2 emission from the older soil carbon pool shows an increasing trend. But in the mature planted forest, its proportion tends to decline, indicating that the stand age may influence the soil carbon sequestration mechanism. The CO 2 emission from the topsoils estimated using the 14 C method is relatively low compared to those by other methods and may be caused by the partial isolation of the young carbon component from the soil aggregates. For more accurate estimation of CO 2 flux, future studies should therefore employ improved methodology for more effective separation of different soil carbon components before isotope analyses.14 C, soil organic carbon turnover, aggregate fractions, Saihanba, afforestation of grassland, stand age Citation:Tan W B, Zhou L P, Liu K X. Soil aggregate fraction-based 14 C analysis and its application in the study of soil organic carbon turnover under forests of different ages.

show abstract

“…The basic approach is that a light fraction is floated on a dense liquid and the denser, or heavy fraction, sinks (Strickland 1987;Sollins et al 1999). The light fraction is typically less degraded, more plant-like, and of more recent origin than the C in the mineralassociated heavy fraction (Gregorich et al 1996;Trumbore and Zheng 1996). Golchin et al (1994a) modified this technique to separate the 'free', unprotected light fraction first, then disrupted aggregates to separate the "occluded", aggregate-protected light fraction from the dense fraction.…”

Section: Fractionation Of Soil Organic Mattermentioning

confidence: 99%