Enzymic and chemical analysis of particulate organic matter from a boreal river

Abstract

SUMMARY. 1. Benthic particulate organic matter (POM) was collected from a shallow pool of a fourth order boreal stream and sorted into seven size fractions ranging from 63 to >4000μm. Each size fraction was analysed for fibre, total phosphorus, and total Kjeldahl nitrogen. Microbial activity was measured by oxygen consumption and characterized by assaying for eleven classes of exoenzymes including cellulase, phenol oxidase, peroxidase, phosphatase and sulphatase.2. Indices of detritus quality such as C/N, C/P, percent lignin, and microbial respiration showed improvement with decreasing particle size. Three covarying exoenzyme groups were identified: a carbohydrase‐phosphatase group that included eight enzymes, a phenol oxidase‐peroxidase group, and sulphatase. The activity of the carbohydrase‐phosphatase group, was significantly correlated with microbial respiration and the carbohydrate content of the POM. Phenol oxidase‐peroxidase activity was correlated with lignin content for POM greater than 250 μm, but activity increased markedly in the two smallest size fractions even though the lignin content of the POM continued to decline, Sulphatase activity was inversely related to particle size over the entire range.3. The changes in microbial activity with particle size were attributed to the increasing surface area to volume ratio of smaller particles and to an ecological succession in the microbial community.