Seminar: Marion Schrumpf

Mineral associated organic matter (MAOM) plays an important role for soil carbon persistence, so that it is important to understand its formation. Recent years led to change in paradigm suggesting that MAOM is not formed from plant but rather microbial residues. Underlying mechanisms for a preferential stabilization of microbial decomposition products on minerals are, however, unresolved. Since the formation of dissolved organic matter (DOM) is an important prerequisite for sorption to mineral surfaces, we analysed the release of DOM from maize litter, fungal and bacterial residues during three months of incubation and tested the affinity of this DOM to a clay mineral (illite) and an iron oxide (goethite). Results will be compared to (1) an incubation experiment, where the formation of MAOM was determined when the same substrates were incubated in direct contact with the two minerals and (2) a long-term field experiment, where the two minerals were exposed to natural conditions, allowing for microbial colonization of mineral surfaces. Results show no universal preference of microbial over plant-residues for DOM sorption and MAOM formation in laboratory experiments, but there are indications, that the relative importance of microbial- versus plant-derived MAOM could be mineral-dependent.