Integrating resource utilization and temperature in metabolic scaling of riverine bacterial production

The openness of streams to external resource inputs complicates the capacity to predict how ecosystem function varies across systems.  We show it is possible to integrate the effects of fluctuating resources and temperature on heterotrophic bacterial production using metabolic scaling theory and the kinetics of extracellular enzyme activity (EEA) associated with the degradation of major nutrient pools.  We analyzed previously published data for two rivers in Ohio (USA).  Kinetic measures, originally assayed at 20 ºC, were scaled to ambient stream temperature (range: 4-31 ºC) using an activation energy of 0.5 eV and converted to estimates of substrate turnover rate (T_s).  Over the course of one year, bacterial production was most highly correlated with protein utilization (R² 0.49-0.52) and most weakly correlated with carbohydrate utilization (R² 0.09-0.15).  Carbohydrate consumption was predominant in autumn and winter and protein consumption was predominant in spring and summer, corresponding to seasonal dynamics in plant litter inputs and algal production, respectively.  The substrate T_s of the six enzymes, when summed, was similar in magnitude to and strongly correlated with bacterial production (R² 0.56).  This approach could be used to compare systems along gradients where resource, rather than temperature, effects on ecosystem function are of greater magnitude.