D- and L-amino acid metabolism in soil

Abstract

The rates of D- and L-amino acid-induced-respiration in 11 different soils were determined. D-alanine induced respiration was either less than or not significantly different from L-alanine-induced-respiration, depending on the soil. For all 11 soils, D-glutamine and D-glutamic acid induced respiration rates were significantly less than those of the corresponding L-amino acids. Thes observations are consistent with the slower rates of D-alanyl-D-alanine compared with L-alanyl-L-alanine induced respiration and of D-glutamine induced ammonification compared with L-glutamine induced ammonification. The rates of L-amino acid induced respiration for all 11 soils were significantly correlated with the size of the soil microbial biomass (R2=0.90, 0.88 and 0.93 for L-alanine, L-glutamine and L-glutamic acid, respectively) and therefore provide an alternative basis for determining soil microbial biomass. Although the rates of D-amino acid induced respiration were also correlated with soil microbial biomass (R2=0.90, 0.79 and 0.61, for D-alanine, D-glutamine and d-glutamic acid, respectively), the D-glutamine and D-glutamic acid-induced-respiration rates accounted for a smaller fraction of the variation in soil microbial biomass than the rates of respiration induced by the other amino acids