Fig. 2: Soil cyanate concentrations and abiotic reactions of cyanate.
From: Cyanate is a low abundance but actively cycled nitrogen compound in soil
a Map of Europe displaying the 46 soil sampling sites: G, grassland; F, forest; P, pasture; A, arable. b Soil cyanate concentrations (extracted using 1 M KCl) plotted as a function of soil pH in 0.01 M CaCl2. The dashed line denotes the soil pH threshold above which cyanate was detectable in all soil samples. c Acid–base dependency of cyanate and isocyanic acid as a function of pH (HNCO ⇄ H+ + NCO−; pKa = 3.66 at 20 °C). The orange dotted line shows the predicted adsorption isotherm of a 10−4 M cyanate solution on hydrous ferric oxide (a major component of soil influencing stabilization of compounds) as a function of pH redrawn from Dzombak et al.43. The equilibrium surface complexation constant was estimated based on correlations of acidity constants and surface complexation constants fitted to adsorption data for other inorganic ions28. d Standardized rates (kstd; at 20 °C) of combined abiotic cyanate/isocyanic acid decomposition to ammonium (Eqs. (6)–(8), rate constants from Equations 9-11), the reaction of cyanate with ammonium to urea (Eq. (3), rate constants from Eq. (5)) and the reaction of isocyanic acid with the amino group of glycine (Eq. (12), rate constants from Eq. (13)). Note that kstd are plotted on a logarithmic scale.
