Journal
MICROBIAL ECOLOGY
Volume 74, Issue 3, Pages 534-549Publisher
SPRINGER
DOI: 10.1007/s00248-017-0976-0
Keywords
Radiocarbon; C-14; Ultra-high-resolution mass spectrometry; FT-ICR MS; DOM quality
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Funding
- German Federal Ministry of Education and Research [02WT1290A]
- European Regional Development Funds (EFRE-Europe funds Saxony)
- Helmholtz Association
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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 via C-14 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.
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