PNNL

Abstract

The molecular diversity of dissolved organic matter (DOM) in soil depends onthe stage of plant litter decomposition and microbial metabolism. Yet thecontributions of catabolic and anabolic processes on DOM molecular diver-sity, and their consequences for organic carbon mineralization, remainunclear. To address this question, we used an 18O-H2O isotope-labellingapproach to track microbial transformation of DOM during blue grama grass(Bouteloua gracilis) decomposition and determine how these processes altermolecular diversity. Here, we show that 18O-isotopically labeled compoundsindicate that microbially produced DOM increases functional moleculardiversity (recognizing compound dissimilarity) during early decomposition(days) but not at later stages (months). Furthermore, carbon mineralizationfrom DOM is most strongly correlated with molecular weight, highlighting therole of chemical properties in regulating microbial decomposition. Our find-ings suggest that early microbial catabolic and anabolic metabolism enhancesDOM molecular diversity, whereas later decomposition favors the accumula-tion of fewer, recycled microbial compounds.