Organic matter was extracted with pyrophosphate-NaOH buffer, pH 8.0 from the 02 horizon of a hardwood forest and exposed to 15S-methionine for 18 h to allow the incorporation of the aminoacid into the extract. Compared with other amendments, supplementation of the incorporation medium with Na2SO4 yielded the highest recoveries of the labelled organic matter. This material was chemically recalcitrant, requiring treatment for 6 h at 121°C with 6 m NaOH for complete release of the incorporated methionine. A and B horizon soils from several forests were exposed to labelled material following dialysis to remove unlabelled components and a minor 35S-labeIled component. All samples began to release 35S-methionine after 48 h. Further metabolism of this amino-acid included mineralization and conversion to cysteine. A portion of the sulfate-S generated from mineralization was incorporated into organic matter and was recovered only by acid and alkali extraction. 35S-labelled methionine and cysteine were also found in these latter fractions, indicating that these amino-acids had been directly incorporated into organic material during exposure.
ASJC Scopus subject areas
- Soil Science