title: Tracing Aquatic Priming Effect During Microbial Decomposition of Terrestrial Dissolved Organic Carbon in Chemostat Experiments.
abstract: Microbial decomposition of terrestrial carbon may be enhanced by the addition of easily decomposable compounds, a phenomenon referred to as priming effect. We investigated the microbial decomposition of terrestrial dissolved organic carbon (DOC) in one-stage and two-stage flow-through cultures (chemostats) in the absence and presence of growing phytoplankton as phytoplankton-derived organic matter might facilitate the mineralization of more refractory terrestrial compounds. Peat water and soil leachate were used as terrestrial substrates, and only slight DOC decomposition was observed in the absence of phytoplankton for both substrates. A priming effect was revealed via14C data. Priming was more pronounced for the peat water substrate than for the soil leachate. The total DOC concentrations increased for both substrates in the presence of phytoplankton due to exudation and cell lysis. Samples from the soil leachate experiments were analyzed using ultra-high-resolution mass spectrometry (FT-ICR MS). Predominantly, the same saturated, aliphatic molecules with H/C ratios >1.5 were completely decomposed in the absence and in the presence of phytoplankton. The decomposition of more stable molecules differed in their intensity. Oxidized and unsaturated molecules with H/C ratios <1.0 and O/C ratios >0.4 were more strongly decomposed in phytoplankton presence (i.e., under priming). We conclude that an aquatic priming effect is not easily detectable via net concentration changes alone, and that qualitative investigations of the DOC processed by bacterial decomposition are necessary to detect aquatic priming.
authors.affiliation: Department of Lake Research, Helmholtz Centre for Environmental Research - UFZ, Brückstr. 3a, 39114, Magdeburg, Germany. karoline.morling@ufz.de.
authors.forename: Karoline
authors.initials: K
authors.lastname: Morling
authors.affiliation: Department of Analytical Chemistry, Helmholtz Centre for Environmental Research - UFZ, Permoserstr. 15, 04318, Leipzig, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Raeke
authors.affiliation: Department of Lake Research, Helmholtz Centre for Environmental Research - UFZ, Brückstr. 3a, 39114, Magdeburg, Germany.|Department of River Ecology, Helmholtz Centre for Environmental Research - UFZ, Brückstr. 3a, 39114, Magdeburg, Germany.
authors.forename: Norbert
authors.initials: N
authors.lastname: Kamjunke
authors.affiliation: Department of Analytical Chemistry, Helmholtz Centre for Environmental Research - UFZ, Permoserstr. 15, 04318, Leipzig, Germany.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Reemtsma
authors.affiliation: Department of Lake Research, Helmholtz Centre for Environmental Research - UFZ, Brückstr. 3a, 39114, Magdeburg, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Tittel
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D005858:Germany; D006812:Humic Substances / Q000032:analysis*; D013058:Mass Spectrometry; D012987:Soil / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D014867:Water / Q000737:chemistry*
chemical_list: D006812:Humic Substances; D012987:Soil; D014867:Water
keywords: 14C; DOM quality; FT-ICR MS; Radiocarbon; Ultra-high-resolution mass spectrometry