Measurements of respiration, incorporation of litter carbon into soil fractions, and microbial community data using mineral-amended soils

Soil was collected from a commercial farm near Glassonby, Penrith and amended with pristine minerals (Kaolinite, Montmorillonite or Goethite) to create soil mineral treatments. Two 13C labelled litters were prepared in-house and added to soils to investigate the effect of litter quality and soil mineralogy on soil organic matter formation. The laboratory experiment was carried out at UK Centre for Ecology & Hydrology in Lancaster and soils were incubated under controlled conditions for 126 days. Respiration of litter-C was quantified by headspace CO2 and 13CO2 analysis on microcosms throughout the 126-day duration of the experiment and application of a two-component isotope mixing model. Concentrations of CO2 were analysed on a calibrated PerkinElmer Autosystem XL Gas Chromatograph. δ13C values of CO2 were analysed using a Picarro cavity ring-down spectrometer (model: G2201-I, Picarro, Inc. CA, USA). For enriched samples the instrument was calibrated for δ13C-CO2 using in-house prepared gas standards of 97.7 ‰ and 815 ‰. Litter carbon in soil fractions was determined by physicochemical density soil fractionation, and fractions analysed for C and δ13C using a Costech ECS-4010 Elemental Analyser (Costech Analytical Technologies, USA) coupled to a calibrated (cane sugar (−11.64 ‰), beet sugar (−26.03 ‰), enriched glucose (197.90 ‰) (IsoAnalytical, UK)) CRDS Picarro G-2131i isotopic analyser (Picarro Inc. CA, USA) and application of a two-component isotope mixing model. Bacterial and fungal community compositions were assessed using 16S rRNA and ITS2 amplicon sequencing using the Illumina MiSeq platform with V2 500 cycle chemistry. Sequences were processed using the DADA2 pipeline to trim, quality-filter, de-noise, de-replicate, generate amplicon sequence variant tables and assign taxonomies.