Microbial Extracelular Enzymes and Biodegradation in Boreal Freshwaters

U. Münster, Lammi Biological Station, University of Helsinki, FIN-16900 Helsinki, Phone: +358-36311152, Fax; +358-363111166

Freshwaters are essential parts of northern boreal environments (NBEs) and they contribute significantly to its ecosystem structures, function and resilience. As NBEs are considered as important players of global bio- geo-chemical cycles there is increasing interest in mechanisms and pathways of its carbon, nitrogen and phosphorus processing and cycling. A major part of these three essential elements are located in natural organic matter (NOM) with highly recalcitrance to degradations. In aquatic ecosystems two major cleaving pathways of NOM degradations can be defined: 1. Abiotic cleaving steps via photo chemical reactions and 2. Microbial cleaving steps via bio-catalysis. This contribution tries to address the importance of bio-catalysis in nutrient cycling and bio-polymer processing. Examples will be given of microbial extracellular enzyme (MEE) activities in aquatic boreal interfaces and its contribution to phosphorus, nitrogen and carbon processing. Special focus will be paid to spatial and time variances of MEEs in small boreal forest lakes, the main contributors to MEE activities, kinetic aspects, effects of humic substances (HS) on MEE activities and some aspects of bio-polymer cleaving mechanisms.