Reduced legacy precipitation decreases microbial community growth efficiency and alters soil organic carbon in a California grassland

Data and data analysis also shown in: https://github.com/linneakh/CA_grassland_omics/FTICR: Files included with and without blanks/controls. Data was acquired using a 7 T Bruker ScimaX FTICR-MS operated with quadripolar (2×) detection and located in the Environmental Molecular Science Laboratory at Pacific Northwest National Laboratory (Richland, WA, USA). External calibration was performed using sodium trifluoracetic acid followed by shimming of the magnet to minimize 1× harmonic resonance peaks and tuning to optimize spectra for peak intensity, shape and resolution over the m/z range 200–1000. Extracts were direct infused into the electrospray source in negative ion mode at a voltage of +4 kV, temperature of 200 °C and dry gas flow of 4 L/min, in randomized order using a custom automated cart. Ion accumulation time was set to 10 ms and 2.1 s transients were coadded over 300 acquisitions in an 8 MW time domain for an estimated average resolution of ∼680K at m/z 400. Internal recalibration of each spectrum, post-acquisition, was performed with calibration lists of standard OM components. Peak picking was performed in Data Analysis using a signal to noise ratio (S/N) threshold of 7, a relative intensity threshold of 0.01 and an absolute intensity threshold of 100,000.CO2: Headspace gas samples (5 mL) were collected at each soil harvesting time point with a gas-tight syringe and transferred to 20 mL Wheaton serum bottles that had purged and filled with N2 (1 atm). Total headspace CO2 was quantified via gas chromatography equipped with a methanizer paired with a flame ionization detector (GC2015, Shimadzu).