Uptake and metabolism of two amino acids by anaerobic microorganisms in four diverse salt-marsh soils

The anaerobic microbial uptake of alanine and aspartic acid was determined in 4 diverse salt-marsh soils (tall and short Spartina alterniflora, creek bank, and mud flat). Uptake in soil slurries was determined by the radioisotopic tracer technique at one substrate concentration (<250 pmoles cm^-3). Dissolved free alanine and aspartic acid concentrations in the interstitial nutrient pool ranged from approximately 1 to 500 pmoles cm^-3. In the short S. alterniflora soil, maximum microbial uptake of alanine was found at a depth of 10 cm (8.32 pmoles cm^-3 h^-1); in the tall S. alterniflora soil maximum uptake was at 20 cm (23.4 pmoles cm^-3 h^-1). The utilization of aspartic acid appeared constant over the depth interval investigated (0 to 60 cm). The turnover times of alanine and aspartic acid in the tall and short S. alterniflora soils ranged from 5 to 25 h and 40 to 100 h, respectively. The percent of the labeled alanine and aspartic acid taken up that was mineralized by tall and short s. alterniflora microbenthos ranged from 20 to 50% and 5 to 20%, respectively.