Abstract: The assimilation of sulfur from six different compounds by the microbial biomass of an Adirondack forest soils was studied. An attempt was made to estimate the relative rate of sulfur incorporation from the compounds and from soil organic matter, by measuring change in the microbial biomass sulfur content. The biomass sulfur content increased most rapidly in response to S supplied as chondroitin (ester) sulfate, and progressively less rapidly from S supplied as inorganic sulfate, L-cysteine, L-methionine, tebuthiuron (an herbicide), and native soil sulfur. Sulfur content of the biomass decreased in response to oryzalin, another S-containing herbicide.
It was found in the Adirondack forest soil studied that sulfur was not limiting to microbial activity, while carbon, nitrogen and possibly phosphorus, were. Thus the rate of sulfur incorporation could be stimulated markedly by addition of glucose, nitrate, and phosphate. The assimilation of S from C- and N-containing organic compounds may also have been stimulated by direct growth and increase in numbers of cells in response to the available C and N. S assimilation from inorganic and chondroitin sulfate appeared to be a more temporary phenomenon of accumulation of the S within cells without any marked increase in metabolism or numbers. This work showed the usefulness of the microbial biomass sulfur technique in forest soils.
Arylsulfatase activity was not found to be a useful indicator of sulfate mineralization or ester sulfate dynamics in these soils.
Sulfur from tebuthiuron was incorporated into soil humic matter to a greater degree than S from oryzalin. It is unclear whether any sulfur from the herbicides was actually assimilated by the soil microorganisms. Oryzalin appeared to exert an inhibitory effect on sulfur uptake, and attempts failed to enrich for organisms capable of metabolizing either herbicide as a sole C and S source.
Effects of S inputs as herbicides or sulfate from acid deposition are discussed in light of this study. The important contribution of native organic sulfur constituents may be comparable or greater in magnitude than the anthropogenic inputs. Organic forms may be a major potential source of sulfate, and must be considered in conjunction with exogenous inputs in assessing impact on soil microbial populations.