Does Microbial Priming Influence the Turnover of Blue Carbon in Aquatic Systems?

As sea level rise progresses, the carbon stored in coastal systems, commonly referred to as blue carbon, is at risk of being lost and transported to estuarine waters. However, the bioavailability of this ancient carbon is not yet known, nor is the prevalence of priming effects in the conversion of this carbon to CO₂. There has been increasing recognition that ancient carbon can be bioavailable in certain environmental contexts, causing a re-evaluation of the age-bioavailability paradigm. This study was conducted to investigate the susceptibility of ancient blue carbon to microbial priming effects through a series of laboratory incubations, paired with metabolomic and metatranscriptomic analyses. Treatments were (1) a peat treatment, (2) an algal treatment, (3) a peat + algae treatment (i.e. primed treatment) and a (3) seawater control. Ancient peat (2 m depth) was collected from a mangrove swamp and used as substrate for peat treatments. ¹³C-labeled algal biomass was used as the substrate for algal treatments. All incubations were inoculated with a mixed microbial consortium isolated from estuarine waters adjacent to the mangrove swamp. Four replicates were analyzed for each treatment. An initial and final (210 hours) timepoint was collected for each treatment and ¹³CO₂ and ¹⁴CO₂ were analyzed to determine the relative contributions of algal and peat substrates, respectively. Internal metabolites and transcript abundances were evaluated to determine the microbial drivers of blue carbon priming in aquatic systems. This work provides further investigation into the mechanisms of priming in aquatic systems, and the vulnerability of blue carbon to global change.