Stabilization of recent soil carbon in the humid tropics following land use changes: evidence from aggregate fractionation and stable isotope analyses

Abstract

Quantitative knowledge of stabilizationand decomposition processes is necessary to understand, assess and predict effects of land use changes on storage and stability of soil organic carbon (soil C) in the tropics. Although it is well documented that different soil types have different soil C stocks, it is presently unknown how different soil types affect the stability of recently formed soil C. Here, we analyze the main controls of soil C storage in the top 0.1 m of soils developed on Tertiary sediments and soils developed on volcanic ashes. Using a combination of fractionation techniques with 13 C isotopes analyses we had the opportunity to trace origin and stability of soil carbon in different aggregate fractions under pasture and secondary forest. Soil C contents were higher in volcanic ash soils (47-130 g kg -1 ) than in sedimentary soils (19-50 g kg -1 ). Mean residence time (MRT) of forest-derived carbon in pastures increased from 37 to 57 years with increasing silt + clay content in sedimentary soils, but was independent from soil properties in volcanic ash soils. MRTs of pasture-derived carbon in secondary forests were considerably shorter, especially in volcanic ash soils, where no pasture-derived carbon could be detected in any of the four studied secondary forests. The implications of these results are that the MRT of recently incorporated organic carbon depends on clay mineralogy and is longer in soils dominated by smectite than non-crystalline minerals. Our results show that the presence of soil C stabilization processes, does not necessarily mean that recent incorporated soil C will also be effectively stabilized.

Effect of compaction on microbial activity and carbon and nitrogen transformations in two oxisols with different mineralogy

“…In oxidic soils, especially Oxisols, microaggregation is stronger, which enables them to resist higher compaction pressures. Also, it has been recently shown that aggregation and organic C stabilization depend strongly on soil mineralogy (Paul et al, 2008). This is further supported by results of a field study where the C MIC of a sandy-loam soil was not altered by tractor traffic, possibly because the porous space was not reduced enough to affect the microbial population (Lee et al, 1996).…”

Contribution of a sewage sludge application to the short-term carbon sequestration across a wide range of agricultural soils

“…In this study, a simple approach is presented to discern the effect of sewage sludge application on the short-term SOC pool across a wide range of agricultural soils. The role of soil properties in the C sequestration of recently added carbon was also studied since little is known about this contribution (Paul et al 2008).…”

Soil carbon dynamics following afforestation of a tropical savannah with Eucalyptus in Congo

“…However the potential for carbon sequestration in the soil in these Eucalyptus plantations on savannah is thought to be limited because soil under native savannah is less carbon depleted than cropland soils and because sandy soils do not contain large amounts of carbon relative to finer textured soils (Six et al 2002;Stewart et al 2007Stewart et al , 2008. In any case, the change in soil carbon after afforestation is commonly more pronounced in coarser particle-size fractions (Feller and Beare 1997;Li et al 2005;d'Annunzio et al 2008), which means that recently incorporated soil C is less stabilized than carbon remaining from the native ecosystem (Paul et al 2008).…”