Characterization of soil organic matter fractions from grassland and cultivated soils via C content and δ¹³C signature

Abstract

Variations in (13)C natural abundance and distribution of total C among five size and density fractions of soil organic matter, water soluble organic C (WSOC) and microbial biomass C (MBC) were investigated in the upper layer (0-20 cm) of a continuous grassland soil (CG, C(3) vegetation), a C(3)-humus soil converted to continuous maize cultivation (CM, C(4) vegetation) and a C(3)-humus soil converted to a rotation of maize cultivation and grassland (R). The amounts of WSOC and MBC were both significantly larger in the CG than in the CM and the R. In the three soils, WSOC was depleted while MBC was enriched in (13)C as compared with whole soil C. The relative contributions to the total C content of C stored in the macro-organic matter and in the size fraction 50-150 microm decreased with decreasing total C contents in the order CG > R > CM, while the relative contribution of C associated with the clay- and silt-sized fraction <50 microm increased. This reflects a greater stability and physical protection against microbial degradation associated with soil disruption (tillage) of the clay- and silt-associated organic C, in relation to the organic C in larger size fractions. The size and density fractions from the CG soil showed significant differences in (13)C enrichment, indicating different degrees of microbial degradation and stability of soil organic C associated with physically different soil organic matter (SOM) fractions. Delta(13)C analysis of the size and density fractions from CM and R soils reflected a decreasing turnover rate of soil organic C with increasing density among the macro-organic matter fractions and with decreasing particle size.

Aggregate and soil organic carbon dynamics in South Chilean Andisols

“…In contrast to e.g. Accoe et al (2002), no gradual shift in δ 13 C value towards finer aggregate classes could be observed as a result of increasing decomposition (O'Brien and Stout, 1978). In this study, we could only distinguish two different SOC pools: the MOM and the mineral soil pool.…”

Effects of human land use on the terrestrial and aquatic sources of fluvial organic matter in a temperate river basin (The Meuse River, Belgium)

“…Consequently, SOM decomposition leads to an enrichment in microbial compounds in residual SOM at the expense of plant-derived compounds (Hobara et al 2014;Kaiser and Kalbitz 2012;Malik and Gleixner 2013). In line with this assumption is the observation that DOM in pore-water of agricultural soils can have lower molecular weights and lower aromaticity compared to soils under native vegetation (Accoe et al 2002;Chantigny 2003;Delprat et al 1997;Kalbitz et al 2003). Therefore, one can hypothesize that greater SOM degradation in humandisturbed catchments results in a stronger microbial fingerprint in soil OM that, once exported into the fluvial network, contributes to the above mentioned shift in stream OM composition observed between disturbed and pristine catchments.…”

Anthropogenic disturbance of natural forest vegetation on calcareous soils alters soil organic matter composition and natural abundance of 13C and 15N in density fractions

“…The light fraction obtained by density fractionation primarily represents labile material of relatively recent origin, and we would expect this fraction to reflect 13 C and 15 N values similar to current vegetation (Compton and Boone 2000;Accoe et al 2002).…”

“…Stable isotope data are useful for assessing C and N turnover in SOM density fractions. Because the light fraction from density fractionation primarily represents labile material of relatively recent origin, we would expect this fraction to reflect 13 C and 15 N values that are closer to current vegetation (Compton and Boone 2000;Accoe et al 2002). The heavy fraction, representing older, more humified and amorphous organic compounds, displays relatively enriched d 13 C values (Ehleringer et al 2000).…”