Date of Award

Spring 5-15-2010

Document Type


Degree Name

Bachelor of Science (BS)




College of Science

First Advisor

Vladislav Gulis


Stoichiometry is the ratio of elements in a substance or microbial biomass. This paper investigates microbial stoichiometry and the responses of microbes to dissolved nutrient concentrations and ratios. The current work assesses both autrotrophic and heterotrophic responses to nutrient enrichment: autotrophic and heterotrophic states are defined mainly by ecosystem primary production and respiration. In ecosystems dominated by autotrophic microbes, nutrient enrichment can lead to increased biomass and biomass-specific rates of primary production. Heterotrophic ecosystems rely on subsides of organic carbon from outside the system. Their enrichment with N and/or P can accelerate microbial respiration rates and result in carbon losses from detritus-based systems. The Redfield ratio is relatively unknown for major groups of heterotrophic organisms, especially fungi. The degree to which heterotrophic bacteria and fungi are homeostatic given variable N and P concentrations and ratios in the medium is also unknown. A bacterial community can be more homeostatic in terms of biomass C:P and N:P than a single strain culture, though there is some evidence of non-homeostasis in some bacterial communities. In this experiment, we tested if aquatic fungi are homeostatic, i.e. if their biomass C:N, C:P and N:P ratios change with varying dissolved nutrient concentrations and ratios. We also determined fungal “Redfield ratio”, which appeared to be C90N9P1, on average. Overall, aquatic fungi were capable of maintaining nearly constant stoichiometric ratio of C:N regardless of changes in their resource stoichiometry or concentrations, while fungal C:P ratio varied to some degree depending on medium C:P ratio and P concentration. The 1/H values obtained in this study indicate that fungal biomass is weakly homeostatic with respect to C:P and homeostatic with respect to C:N and N:P. Such studies can provide information on the effects of nutrient enrichment on biogeochemical cycling and energy flow in microbially mediated food webs.

Included in

Biology Commons