Dissipation kinetics of asparagine in soil measured by compound-specific analysis with metabolite tracking

Abstract

Estimating the potential for direct plant acquisition of organic N, in particular amino acids, requires assessment of their turnover times in soil. It is well known from 14C studies that mineralization of amino acids occurs within hours, but mineralization to 14CO2 does not indicate the rate of disappearance of the intact amino acid or the possible formation of metabolites during amino acid dissipation. We here used compound-specific isotope analysis with metabolite tracking to investigate the dissipation rate of universally labeled intact 13C15N-asparagine at two concentrations and the subsequent formation of compounds closely related to 13C15N-asparagine metabolism over 3 h in agricultural soil. 13C15N-asparagine was rapidly dissipated with half-lives of 55 and 231 min for the low and high 13C15N-asparagine concentrations used. Universally labeled aspartic acid and interestingly also universally labeled glutamic acid were detected in soil. This highlights the fast turnover of amino acid in soil and that the estimation of concentration of the formed compounds is important when evaluating plant available organic N. Efficiency of the compound-specific analysis showed to be a powerful technique in following the pathway of amino acids in soil.