Tracking the Changes of DOM Composition, Transformation, and Cycling Mechanism Triggered by the Priming Effect: Insights from Incubation Experiments

The priming effect (PE) is recognized as an important mechanism influencing organic matter transformation in aquatic systems. The land-ocean aquatic continuum (LOAC) has received large quantities of dissolved organic matter (DOM) from various sources, which is an ideal interface for PE research. Here, we investigated the PE process by utilizing such a coastal environment to explore the turnover of DOM in the LOAC system. Suwannee River natural organic matter was selected as the background, and various external environmental samples were introduced to track the changes of organic carbon. The PE process together with the variations of DOM sources, compositions, and structures was characterized. Generally, river and estuary environments exhibited a positive PE, while the offshore zone showed a negative effect. Additionally, nutrients, salinity, and DOM composition all contributed to the PE. After the incubation, the feature of carbon sources transferred from terrestrial to autochthonous. The carbonyl and alcohol functional groups significantly decomposed, while the methyl and methylene groups increased and heteroatoms further accelerated the PE process. The data also shows that special parameters and molecular markers can be utilized to track the carbon response to the PE. This research indicates that the change of carbon flux and the imbalance of its budget in aquatic systems could be partially explained from the perspective of the PE.