Lampe, Vanessa (2018) The priming effect: can the microbial turn-over of deep-sea organic matter be stimulated?. (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 58, XIX pp.

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Abstract

Over time, organic compounds in the marine realm are reworked by microbes. The older the compound becomes, the more alteration it has undergone and the less it is available for further oxidation. It becomes refractory (less bioavailable). However, observations have shown that the microbial utilisation of refractory organic matter can be stimulated, when fresh (and labile) OM is added. This effect is called the priming effect. In the global oceans, large pools of organic matter are stored in the deep-sea, though concentrations of the individual compounds are low. Deep-sea OM is considered as refractory and biologically rather unavailable. This thesis aimed to resolve, whether microbial turn-over of deep-sea OM is limited by it's intrinsic chemical structure and can be stimulated by labile OM priming effect. Alternatively, it was tested whether the dilution of abyssal OM limits it's turn-over and the respective enrichment would enhance it's turn-over (concentration effect). An incubation study was performed: for 30 days, bacteria harvested in the deep Southwest Pacific were incubated under different substrate conditions. To test, whether an increased reworking of abyssal OM could be induced by the addition of labile OM, surface water OM was added to the incubations in one treatment, and an extremely labile mixture of glucose and leucine was added in another. The concentration of deep-sea OM was enriched through ultrafiltration in a third treatment, to test whether increased OM turn-over could be detected. All treatments were compared to a control group, in which microbes and substrate OM both originated from the deep-sea. Over the course of the incubation period, various biogeochemical and biological parameters were sampled. The concentration effect hypothesis could not be clearly rejected nor accepted. Even though no clear signs of RDOM degradation could be detected through the analysis of various biogeochemical parameters, the microbial activity was clearly enhanced compared to the control. The priming effect hypothesis found support in various analyses. Most strikingly, the extremely elevated microbial growth rate after adding labile OM, compared to the control, supports the assumption that OM turn-over increased. Furthermore, after labile OM amendments, TOC and DOC concentrations decreased to values lower than their initial concentrations, indicating degradation of the native abyssal DOM. Reviewing the findings of this study, the molecular properties seem to influence the microbial degradation of refractory dissolved organic matter, rather than it's concentration.

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