PNNL

Abstract

Rapid microbial growth on simple substrates in the early phase of plant litter decomposition is viewed as an important component of soil organic matter (SOM) formation but the nature of the substrate pool and interactions with microbes is unresolved. Further, dissolved organic carbon (DOC) is composed of a mixture of plant and microbial inputs due to the active microbial enzymatic activity needed to decompose plant litter, and the necromass produced by microorganisms at the end of their lifecycle. While DOC offers readily available substrate for microbial consumption, its composition reflects past metabolic activities which dictate the relative contributions of different compound classes such as proteins, lipids, and other chemical compound types. Specifically, we wanted to know if chemical compound types can be predictive of increased concentration and persistence of DOC. Using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) on microcosm samples from early phase litter degradation, we found that proteins and tannins are the compounds with the strongest correlation to DOC concentration. Proteins correlated positively with DOC concentration, while tannins and condensed hydrocarbons correlated negatively with DOC. Through random forest, neural network, and indicator species analyses, we identified bacterial and fungal taxa associated with DOC concentration and additionally identified connections between microorganisms and DOC chemical composition. This research links DOC concentration with microbial production and/or decomposition of specific metabolites to improve our understanding of microbial metabolism and carbon persistence.