PNNL

Abstract

As sea level rises, previously sequestered blue carbon (BC) can be exported offshore as particulate or dissolved organic matter (POM or DOM) where it may be re-mineralized or sequestered. The priming effect, or interactive effects of OM turnover in the presence of a mixed substrate, is well described in soils, but is still debated in aquatic systems. However, priming may contribute to enhanced BC re-mineralization in coastal environments, particularly in the presence of labile, algal-derived DOM. We examined mangrove-derived DOM turnover in a lab incubation, using a mangrove peat leachate, a 13C-labeled algal leachate, and combined peat and algal leachates (primed). POM and DOM were assessed; microbial metatranscriptomes were evaluated; and DOM was characterized with high resolution mass spectrometry. Stable isotopes indicated rapid allocation of algal-derived DOM into POM. When comparing relative changes in CO2, the algal treatment had the greatest relative increase in CO2. However, the primed and peat treatments had the greatest amount of dissolved organic carbon (DOC) removed, significantly greater RNA concentrations, similar total CO2 released, and less abundant pathways for the biosynthesis of nitrogen-rich, non-polar compounds relative to treatments without peat. This suggests that while total CO2 did not increase under priming conditions, it is likely that the addition of a peat substrate may promote microbial biomass production relative to CO2 production. This study highlights that more targeted studies investigating the specific mechanisms of priming are necessary to address the molecular and microbial transformations associated with priming in aquatic systems.