Shining Light on Priming in Euphotic Sediments: Nutrient Enrichment Stimulates Export of Stored Organic Matter

Abstract

Estuarine sediments are important sites for the interception, processing, and retention of organic matter, prior to its export to the coastal oceans. Stimulated microbial cometabolism (priming) potentially increases export of refractory organic matter through increased production of hydrolytic enzymes. Using the microphytobenthos community to directly introduce a pulse of labile carbon into sediment, we traced a priming effect and assessed the decomposition and export of preexisting organic matter. We show enhanced efflux of preexisting carbon from intertidal sediments enriched with water column nutrients. Nutrient enrichment increased production of labile microphytobenthos carbon, which stimulated degradation of previously unavailable organic matter and led to increased liberation of "old" (6855 ± 120 years BP) refractory carbon as dissolved organic carbon (DOC). These enhanced DOC effluxes occurred at a scale that decreases estimates for global organic carbon burial in coastal systems and should be considered as an impact of eutrophication on estuarine carbon budgets.

Exploring the Complexities of Dissolved Organic Matter Photochemistry from the Molecular Level by Using Machine Learning Approaches

“…Analysis of three explicitly photochemical molecular pools (probability > 0.95) indicated that explicitly photolabile MFs exhibited higher aromatic and humifaction degree (Figure ), which is consistent with previous irradiation-based studies, ,, also suggesting that the partially oxidized processes are probably predominant in estuarine ecosystems. Moreover, the photolabile pool had the highest CHOS% among the three pools (Figure and Figure ), supporting its facile photochemical degradation as reported from the deep sea, , porewater, and acid mine drainage, with the potential products of climate-impacting gases carbonyl sulfide, dimethyl sulfide, or methanesulfonic acid. Significant amounts of N-containing compounds produced after photoirradiation were also found in samples from both natural and anthropogenic sources and were interpreted by the photoinduced incorporation of dissolved organic nitrogen into DOM. , The photoresistant pool was dominated by the HU group (Figure ) that is also known to be biologically recalcitrant to heterotrophic microbes .…”

“…To study the potential photochemical reactivity of samples without employing irradiation experiments, a favorable practice is to compare the MFs occurring in samples from various aquatic ecosystems with the classified MFs acquired from previously performed irradiation experiments. − Despite the success of this “molecular matching” approach in evaluating the photochemical quality of the samples, many concerns remain. First, considering the complexity of the DOM transformation, the relationship between the classes of photochemistry related MFs and their chemical composition is complicated and probably nonlinear, which cannot be simply elucidated through the molecular matching approach.…”

Lake Chemodiversity Driven by Natural and Anthropogenic Factors

“…These nutritional parameters contributed strongly to the determination of DOM composition. Nutrient enrichment may increase the degradation of previously unavailable DOM by increasing the production of hydrolytic enzymes from stimulated microbial cometabolism . Eutrophication promotes the transformation of tyrosine-like components to protein-like components with elevated humification and molecular weight .…”

The impact of mobile demersal fishing on carbon storage in seabed sediments

“…On the other hand, the transfer of high‐quality OC from the surface to deeper layers may prime microbial communities and in this way stimulate degradation of more refractory OC found in deeper sediment layers (Middelburg, 2018 ; van Nugteren et al, 2009 ). This can lead to significantly increased total OC remineralization rates, although the process is known to vary between environmental settings (Bengtsson et al, 2018 ; Riekenberg et al, 2020 ; van Nugteren et al, 2009 ).…”