Root phenolics drive shifts in microbial community and prime decomposition in forest soil

Root-derived phenolics perform various functions in soil ranging from microbial substrate to toxin, yet their contribution to rhizosphere priming remains unclear. Therefore, the aim of this study was to investigate how major root phenolics influence soil organic matter (SOM) dynamics and interact with other labile C amendments.We performed a 38-day incubation experiment to determine whether root phenolics (benzoic acid, caffeic acid and catechin) facilitate or inhibit SOM decomposition in a glucose-amended forest soil. Changes in priming, substrate use, fungal and bacterial community composition, and microbial abundance and activity were assessed over time using 13C-stable-isotope tracing, DNA-based molecular methods and enzyme assays.Phenolics inhibited microbial activity and abundance to varying degrees. Yet, benzoic acid was the only compound producing a substantial priming effect leading to a 21% increase in SOM decomposition, which was amplified in glucose-amended soils. This stimulation in microbial activity was associated with an increase in Paraburkholderia and ß-1,4-glucosidase activity. Phenolics drove microbial community shifts in glucose-amended soils with negligible interactive effects.Phenolic priming of SOM decomposition is associated with microbial community shifts, which were amplified in the presence of glucose. This evidence supports the need for considering phenolics and interactions among root exudates as priming mechanisms in the rhizosphere.