Dissolved carbon leaching in and from soils plays an important role in C transport along the terrestrial-aquatic continuum. However, a global overview and analysis of dissolved carbon in soil solutions, covering a wide range of vegetation types and climates, is lacking. We compiled a global database on annual average dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) in soil solutions, including potential governing factors, with 762 entries from 351 different sites covering a range of climate zones, land cover types and soil classes. Using this database we develop regression models to calculate topsoil concentrations, and concentrations vs. depth in the subsoil at the global scale. For DIC, the lack of a roportional globally distributed cover inhibits analysis on a global scale. For DOC, annual average concentrations range from 1.7 to 88.3 (median=25.27) mg C/L for topsoils (n=255) and from 0.42 to 372.1 (median=5.50) mg C/L for subsoils (n=285, excluding lab incubations). Highest topsoil values occur in forests of cooler, humid zones. In topsoils, multiple regression showed that precipitation is the most significant factor. Our global topsoil DOC model (R2=0.36) uses precipitation, soil class, climate zone and land cover type as model factors. Our global subsoil model describes DOC concentrations vs. depth for different USDA soil classes (overall R2=0.45). Highest subsoil DOC concentrations are calculated for Histosols.

This is the Supplementary Information (SI) in addition to the article 'Global database and model on dissolved carbon in soil solution' by Langeveld et al.Below a brief overview of the SI content is given. For questions, please don't hestitate to contact the corresponding author, Joep Langeveld (j.j.langeveld@uu.nl & joeplangeveld@gmail.com).SI contentSI_1-The database on dissolved C in soil solution-The bibliography of the literature used in the database-Instructions file (see further this file)SI_2-netcdf with the modelled annual average DOC concentration (mgC/L) in topsoil-netcdf with the modelled annual average DOC concentration (mgC/L) in subsoil(1m)The modelled DOC concentration in topsoil and subsoil are provided as five-yearly datasets on grid for the period 1970-2000. Non-land grid cells are masked. For subsoils, a few cells report 'nan'; then, no infiltration occurs due to only land cover with ice or rock.The data can be opened for analysis in any programming language (e.g. python) or for quick visualisation with e.g. Panoply (https://www.giss.nasa.gov/tools/panoply/)SI_3-fig_SI3.1-fig_SI3.2Boxplots showing top and subsoil DOC concentration (mg C/L) data distributed over sub-climate zones according to Kottek et al. (2006) (fig_SI3.1) and land cover groups (fig_SI3.2).Figures are similar to figure 4b&c, but exclude data for Histosols.Laboratory incubation data are excluded, n=469. Boxplot bars are medians. Whiskers extend up to 1.5 times the interquartile range (IQR) from the lower and upper quartile, unless exceeding the minimum or maximum. Circles are values exceeding the whiskers.SI_4-statistical_testsDetails statistical tests mentioned in the article, including the corresponding text.SI_5-13 figuresSubsoil regressions for DOC relative to the topsoil, for every USDA soil class, except Mollisols. Corresponding numbers are shown in table 4.SI_6Single regression of C/N ratio vs DOC concentrations from the database, for only data from the Spodosol soil class.