Autor:innen:
De Shorn Bramble | Max Planck Institut for Biogeochemistry Jena | Germany
Dr. Ingo Schöning | Max Planck Institut for Biogeochemistry Jena | Germany
Shane Stoner | Max Planck Institut for Biogeochemistry Jena | Germany
Susanne Ulrich | Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
Prof. Dr. Robert Mikutta | Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
Dr. Klaus Kaiser | Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
Prof. Dr. Kai Totsche | Friedrich Schiller University of Jena
Prof. Susan Trumbore | Max Planck Institut for Biogeochemistry Jena
Dr. Marion Schrumpf | Max Planck Institut for Biogeochemistry Jena
The largest share of total soil organic matter is associated with soil minerals, making the formation of mineral-associated organic matter (MAOM) a key factor in the global carbon (C) cycle. Little is known about the effect of mineral type and land use on the extent of MAOM formation, its stability, and age along soil profiles. We addressed this research gap by exposing pristine minerals (an iron oxyhydroxide, goethite, and a clay mineral, illite) for five years to ambient soil conditions at 0, 5 and 30 cm depth in 27 forest plots, and at 5 and 30 cm depth in 27 grassland plots across three regions in Germany. After recovery, the content of organic C (OC) of the minerals was determined by dry combustion. The stability of the mineral-bound C was assessed by sequential extraction with 0.01M CaCl2 and 0.1M Na4P2O7. Radiocarbon was used to determine the 14C age and assess the potential source of the MAOM-C. Results show that irrespective of soil depth, goethite accumulated more OC than illite (on average 0.28, 0.20, and 0.10 mg m-2 mineral surface at 0, 5 and 30 cm depth, respectively for goethite, and 0.09, 0.05, and 0.02 mg m-2 mineral for illite). The amount of MAOM-C that accumulated at 5 and 30 cm depth was similar in forests and grasslands. We further show that in forest, MAOM-C accumulation at 0 cm depth was higher in coniferous forests than deciduous forests. This trend persisted at 5cm depth for goethite. However, at 30 cm depth, both forest types accumulated similar amounts of MAOM-C for both minerals. The proportion of MAOM-C extracted by CaCl2 depended on mineral type, being higher for illite than goethite, but was not affected by land use. Conversely, Na4P2O7-extractable OC was higher for goethite than illite, and was higher in forests than in grasslands at 5 cm but not 30 cm depth. First results show a decline in the 14C content of the MAOM-C with depth. Overall, our results suggest that i) the accumulation and stability of MAOM along the soil profile is mineral dependent, and ii) the effect of land use on the formation and stability of MAOM is limited to the topsoil.