SS2.04 Microbial Stoichiometry and Impacts on Biogeochemistry: From Genes to the Biosphere
Date: Friday, June 14, 2002
Time: 10:15:00 AM
Location: Carson C
Elser, J, J, Arizona State University, Tempe, USA,
KyleM, Arizona State University, Tempe, USA,
Yoshida, T, , Cornell University, Ithaca, USA,
Urabe, J, , Kyoto University, Otsu, Japan,
Bacterial and algal resource limitation and the microbial food web: a test of the light:nutrient hypothesis
The light:nutrient hypothesis (LNH) states that the relative importance of the microbial food web is affected by light:nutrient balance experienced by phytoplankton. We tested this hypothesis in field enclosures by manipulating light intensity and nutrient supply in a P-limited lake in Ontario, Canada. Shading and P-enrichment had little effect on biomass of <1um particles but both decreased it's C:P. P-fertilization did not affect algal or bacterial abundance but shading significantly lowered algal biomass and algal:bacterial abundance. Shading had no effect on heterotrophic nanoflagellates (HNF) but HNF abundance declined strongly with P enrichment coincident with large increases in macrozooplankton accompanying P fertilization. Shading and nutrient enrichment also affected algal resource limitation and the C:P of particles produced by new growth in ways consistent with the LNH. Our data support several aspects of the LHN, including predicted impacts on the microbial food web and C:P stoichiometry. However, some responses were not consistent with the LNH, suggesting that the hypothesis needs to be modified to incorporate indirect effects.