Assessing the priming effect of dissolved organic matter from typical sources using fluorescence EEMs-PARAFAC

Priming effect (PE) is increasingly recognized as an important mechanism in the microbial degradation of dissolved organic matter (DOM) from freshwater to the ocean. However, potential PE during the mixing of DOM from different sources and the effects on different DOM constituents are still largely unknown. This study examined the PE after adding DOM from typical natural and anthropogenic sources (rainwater, fresh plant, leaf litter, and wastewater) into pre-aged river DOM, using dissolved organic carbon (DOC) measurement, absorption spectroscopy, and fluorescence excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC). The plant-derived DOM had a low humic content and was dominated by benzoic acid-like and tyrosine-like fluorescent components (C4 and C5), which showed a high DOC bioavailability of 80%. DOC in rainwater and wastewater also had high bioavailabilities (45%–50%), while DOM in the leaf litter leachate showed high aromaticity, average molecular weight, and humic content but low DOC bioavailability (12%). There was generally limited PE (