Increasing global temperature will undoubtedly affect the
biogeochemistry of aquatic ecosystems. Because heterotrophic
bacteria have such rapid generation times and access to
dissolved organic carbon and dissolved mineral nutrient pools,
they play an important role in the biogeochemistry of all aquatic
ecosystems. Therefore, developing a robust understanding of
how temperature affects natural bacterioplankton communities
is key to understanding how increasing global temperatures will
affect the biogeochemistry of aquatic ecosystems. This thesis
uses a combination of observational, experimental, and
theoretical methods, to develop a mechanistic understanding of
how temperature `affects the metabolism and biomass
composition of natural bacterioplankton communities. An
observational study of 128 lakes in the upper Midwest of the US
evaluates the relationship between biomass C:P ratios, cellular
RNA content, and growth, in situ and discusses how temperature
might affect those relationships. Filter isolated bacterial
communities from two lakes, isolated during two seasons, are
evaluated to determine the affect of temperature and resource
interactions on bacterial growth efficiency. In addition, the
results from these experiments demonstrate how the
relationship between growth and P is affected by temperature,
and show evidence for the seasonal adaptation of natural
bacterioplankton communities to in situ temperatures. Finally,
using information gained from the empirical portion of this
thesis, temperature dependence is added to a variable yield,
“Droop-style” model, to define a mechanistic framework for the
effect of temperature on bacterioplankton communities. Solving
the model at equilibrium (i.e. zero net growth) for residual
resource levels, and using a graphical mechanistic framework
shows how changes in resource requirements, across a thermal
gradient, results in competitive displacement by species adapted
to either warm or cold environments. The results from this
research are consistent with the previously established idea that
the effect of temperature on the metabolism of bacterioplankton
communities is dependent on the level of available resource. In
addition, the results presented here suggest that resources
interact with temperature forcing by structuring the composition
of the bacterial community across thermal gradients. Ed Hall
can be reached at hall0506@umn.edu.