SOIL RESPIRATION INDUCED BY THE D-ISOMER AND L-ISOMER OF A RANGE OF AMINO-ACIDS

The rates of CO2 production from soils amended with the D-and L-isomer s of alanine, glutamine, glutamic acid, histidine, methionine and tryp tophan have been determined in two soils with similar microbial biomas s contents but contrasting qCO(2) (basal respiration/biomass C) values and ergosterol (indicator of fungi) contents. The L-amino acids used include representatives of all the main structural groups and some D-a mino acids rarely encountered in nature. The L-amino acid SIRs were al ways greater than the D-amino acid SIRs, and in most cases the ratio o f L-amino acid-to-D-amino acid SIR (L-to-D ratio) was greater for the soil with lower qCO(2) and smaller fungal biomass. The enhancements of both D-amino acid SIR and L-amino acid SIR following conditioning of the soils with the amino acid substrate for 7d were equally susceptibl e to streptomycin and less susceptible to cycloheximide. These observa tions indicate that the difference between D-and L-amino acid SIRs was not due to gross differences in the proportions of bacteria and fungi in the soils. (C) 1997 Elsevier Science Ltd.