16S rRNA metabarcoding
RNA was extracted from a 2 g sediment aliquot (RNeasy PowerSoil Total RNA kit, Qiagen), quantified (Nanodrop 2000, Thermo Fisher Scientific) and quality-checked (Bioanalyzer 2100, Agilent) as described in Bollinger et al. (2021). A 2 L aliquot of this extract was reverse transcribed to cDNA with random primers (iScript synthesis kit, BioRad) and the V4 region of the 16S rRNA gene was amplified using the primer pair 515Fm (5-GTGYCAGCMGCCGCGGTAA-3) and 806Rm (5-GGACTACNVGGGTWTCTAAT-3) (REF, 98C for 30s, 26 cycles each consisting of 98C for 10s  63C for 30s  72C for 30s, and a final extension for 5min at 72C). The amplified samples were then pooled treatment-wise and library-prepared with the Next Ultra DNA Library Prep Kit for Illumina (NEB, USA) and sequenced on an Illumina MiSeq platform, generating 2300nt paired-end reads by StarSeq, Mainz, Germany.