Enzymes shed light on stream production

Posted on September 21, 2011

Because the metabolic rates of organisms (i.e., the rates at which they obtain and use nutrients and energy) are strongly dependent on body size, temperature, and available food, metabolic approaches can play a useful role in explaining patterns of  biomass production and food web structure.  However, although metabolic processes in freshwater streams are dominated by bacterial activities, the use of bacterial metabolism to model stream production has been hindered by large fluctuations in metabolic rates.  These variations are the result of the fact that a sizeable fraction of the nutrient supply comes from outside the stream and arrives in annual or seasonal pulses.  Consequently, the effects of fluctuating resources on metabolic rates need to be distinguished  from those related to body mass and temperature.  With this aim in mind, it’s been recognised that levels of enzyme activity in streams are good indicators of organic decomposition and bacterial production.  Data on bacterial production and the activity of six extracellular enzymes were collected from Ohio rivers throughout the year.   Over the whole annual cycle, summed enzyme activity was a strong predictor of bacterial production.  However, the activities of the different enzymes varied with season and indicated that bacterial production was based mainly on protein (algal) consumption in spring-summer but carbohydrate (plant litter) consumption in autumn-winter.  This study shows that enzyme approaches can help to reveal patterns of microbial resource-switching in freshwater systems.

Reference:  Sinsabaugh, R.L.  & Follstad Shah, J.J.  2010.   Integrating resource utilization and temperature in metabolic scaling of  riverine  bacterial production.  Ecology, 91(5), 1455–1465.