Nitrogen Rate Drives Dissolved Organic Matter Accumulation and Mowing Constrains Frequency-Dependent Molecular Turnover in Grassland Soils

This dataset accompanies the manuscript “Nitrogen Rate Drives Dissolved Organic Matter Accumulation and Mowing Constrains Frequency-Dependent Molecular Turnover in Grassland Soils.” It contains treatment-level molecular-formula and peak-intensity data obtained by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) for dissolved organic matter (DOM) recovered from water extracts of temperate grassland soils. The samples were collected from a 14-year field experiment at the Inner Mongolia Grassland Ecosystem Research Station, China. The experiment comprised two management regimes—natural growth (NG) and mowing treatment (MT)—and seven nitrogen (N) regimes: a no-N control (CK) and three annual N-addition rates (LN, 10; MN, 20; and HN, 50 g N m⁻² yr⁻¹), each delivered in either 2 or 12 applications yr⁻¹. Equal-carbon aliquots from five replicate soil extracts within each treatment were pooled before PPL solid-phase extraction, yielding one composite FT-ICR MS profile for each of the 14 treatments. Molecular profiles were acquired using a 9.4 T Bruker solariX FT-ICR mass spectrometer with negative-mode electrospray ionization. The dataset contains the union of 8998 unique assigned molecular formulas across all treatment profiles. For each formula, the workbook reports elemental composition (C, H, O, N, and S), observed mass-to-charge ratio (m/z), signed formula-assignment mass error, and instrument-reported peak intensity for each treatment. A peak-intensity value of 0 indicates that the corresponding formula was not detected or did not satisfy the peak-filtering and formula-assignment criteria in that treatment profile; it does not represent a measured zero concentration or definitive chemical absence. The workbook includes four worksheets: (1) README, which summarizes the dataset and provides guidance for interpretation; (2) Data_dictionary, which defines all variables and units; (3) Treatment_metadata, which explains the treatment codes, N-addition rates, delivery frequencies, and numbers of detected formulas; and (4) Assigned_formulas, which contains the complete formula-level dataset. Because the five field replicates were pooled before FT-ICR MS analysis, the treatment profiles represent composite, treatment-level observations. Accordingly, the peak intensities and formula-occurrence patterns are intended for descriptive molecular comparisons and should not be treated as independent biological replicates for inferential statistical analysis. These data are processed, formula-assigned FT-ICR MS peak lists rather than vendor-format raw mass spectra or free-induction-decay files.