Primary Productivity, Heterotrophy, Metabolic Indicators of Stress and Interactions in Algal-Bacterial Mat Communities Affected by a Fluctuating Thermal Regime

摘要

Thermal habitats in effluent cooling waters from production nuclear reactors at the Savannah River Plant are unlike natural thermal habitats in that reactor operations are periodically halted, exposing the organisms growing in these thermal habitats to ambient temperatures for unpredictable lengths of time. Rates of primary production, glucose heterotrophy, and the composition of algal-bacterial mat communities growing along a thermal gradient from about 50 to 35 exp 0 C during periods of reactor operation were studied. Cyanobacteria were the only photoautotrophs in mat communities above 40 exp 0 C while cyanobacteria and eucaryotic algae comprised the photoautotrophic component of mat communities below 40 exp 0 C. The heterotrophic component of these communities above 40 exp 0 C was made up of stenothermic and eurythermic thermophilic bacteria while both eurythermic thermophiles and mesophilic bacteria were found in communities below 40 exp 0 C. Net CO sub 2 -fixation rates during thermal conditions dropped after initial exposure to ambient temperatures. After prolonged exposure of the thermal communities to ambient temperatures, adaptation and colonization by mesophilic algae occurred. Rates of glucose utilization under varying degrees of thermal influence suggested that the heterotrophic component may not have been optimally adapted to thermal conditions. During periods of changing thermal conditions, an increase in the percentage extracellular release of photosynthetically fixed exp 14 CO sub 2 by cyanobacteria and algae and an increase in the percentage of glucose mineralized (respired) by the heterotrophic component of the mat communities was observed. Results of temperature shift experiments indicated that the short-term response of the photoautotrophic component of these communities to thermal stress was an increase in the percentage of photosynthate released extracellularly. (ERA citation 05:019704)