PHOSPHORUS AND IRON AMENDMENTS AFFECT MULTIPLE NITROGEN CYCLING PROCESSES

Nitrogen (N) is a limiting factor in many ecosystems, as a result, microbes have developed methods to acquire and recycle N. However, these processes require investment and thus can be limited by resources like phosphorus (P) and iron (Fe). We performed a stream-side mesocosm experiment, drawing water from a reference stream (East Branch Chagrin River, Kirtland, Ohio) to examine the influence of P and Fe on N cycling processes. 32 flow-through mesocosms were dosed with nutrient combinations of NO3- (250 g/L), PO43- (30 g/L), and Fe3+ (100 g/L) in a fully factorial design. These mesocosms received amendments for 23 days, after which we collected biofilm and sediment to measure N fixation and denitrification rates (acetylene reduction and block, respectively), NH4+ uptake and regeneration (15-N labeled ammonium), and aminopeptidase activity. Preliminary results show that there were no significant differences between treatments for N fixation (ANOVA, p-value=0.232). Meanwhile, the rates of both NH4 regeneration and uptake were highest for mesocosms that received a combination of P and Fe and lowest among N treatments. These higher rates of regeneration in treatments with Fe suggest that Fe is increasing heterotrophic production and the activity of proteins responsible for recycling of NH4. These results suggest that Fe and P may play a role in alleviating N limitation primary through stimulation of internal recycling rather than increased N fixation.

Primary Presenter: Renn Schipper, Kent State University (rschipp1@kent.edu)

Authors:

Renn Schipper, Kent State University  (rschipp1@kent.edu)

Olufemi Akinnifesi, Kent State University  (oakinnif@kent.edu)

Talia Pope, Kent State University  (tpope1@kent.edu)

David Costello, Kent State University  (dcostel3@kent.edu)