Influence of organic-mineral aggregates on microbial degradation of the dinoflagellate Scrippsiella trochoidea

Abstract

Aggregation of particulate organic matter (POM) and mineral grains may result in physical protection of organic matter (OM). To test this, phytoplankton cells of the dinoflagellate Scrippsiella trochoidea were inoculated with a natural bacterial assemblage and incubated with or without the clay montmorillonite. Within 5 h, aggregation of phytoplankton OM and clay resulted in transfer of the majority (∼80%) of OM into the >1.6 g cm −3 density fraction. Degradation of particulate organic carbon (POC), particulate nitrogen (PN), dissolved organic carbon (DOC), and dissolved and particulate total hydrolyzable amino acids (THAA), were modeled with a multi-G approach. Quantity of resistant OM was between two and four times larger during clay incubation relative to clay-free incubation. The two incubations did not exhibit significant differences in degradation state of particulate amino acids nor were there indications of preferential sorption of basic amino acids. The results suggest that a considerable fraction of phytoplankton OM can become resistant, at least on a timescale of weeks, mostly due to aggregation of POM and clay mineral grains.