Response of root exudates and bacterial community to N fertilization and termination methods in Avena sativa L. as a winter cover crop model

Agricultural practices associated with winter cover crops (WCCs) and nitrogen (N) fertilization could change the amount and composition of root exudates by altering the plant metabolism, ultimately affecting their interaction with microorganisms. The goal of this study was to evaluate the combined effect of N fertilization (N0 and N100, kg N ha⁻¹), and spring growth termination methods (M: DQ, chemical suppression; CM, mechanical cut; SS: no suppression) of oat (Avena sativa L.) as a WCC model, on the chemistry of root exudates and the microbial community structure in a greenhouse. The chemical characterization of root exudates was performed by Fourier transform infrared spectroscopy (FTIR), while total phenols (TPC) and phosphorus (P) contents were measured in aqueous extracts of root exudates. Bacterial community structure and composition were assessed through sequencing in Illumina MiSeq followed by QIIME2 analysis. The root exudation pattern of oat and P content in exudates showed significant differences among M, while a significant interaction was observed between N fertilization and the M for TPC. At the rhizospheric bacterial community level, differences in composition were detected between M. Overall, both termination methods (DQ and CM) negatively affected genera considered beneficial for the plants, while the chemical suppression of oat increased the abundance of some other genera with species identified as soil-borne pathogens in the rhizosphere. FTIR spectral profiles in exudates of oat were different in plants terminated by CM compared to SS and DQ, regardless of N fertilization, partially explaining the shifts found in the composition of the rhizospheric bacterial community. Considering that decaying roots of the terminated WCC remain in soil, future studies should address whether the termination methods have effect on the next crop and its microbiome.