Humans continuously alter the relative availability of Nitrogen within the biosphere leading to eutrophication of water resources. A great diversity of nutrient loads inundates our freshwater ecosystems, leading to varied responses in their elemental content, community structure, and function. To determine impacts of increased and alterations of reactive nitrogen and phosphorus and N:P ratios, we utilized the model system Sarracenia purpurea (Northern pitcher plant) which contains an entire aquatic ecosystem and is a statistically powerful model system. S. purpurea is long lived, contains numerous self-replicates in the form of tubular leaves, has complex trophic interactions, and receives most of its nutrients from atmospheric deposition. In the summer of 2018, we conducted an ecological press experiment in Molly Bog, VT for 11 weeks. 38 pitcher plants had their aquatic microcosm removed and replaced with a nutrient cocktail based on a regression design of 5 concentrations of N (0.0875 to 1.4 mg/l), and P (0.025 to 0.4 mg/l), and 9 N:P ratios. At the end of 11 weeks we collected each ecosystem component; pitcher fluid, plant tissue, invertebrates, detritus, algae, and microbial communities and analyzed elemental content, community structure, and function.
Results/Conclusions
From the press experiment, we found pitcher fluid within S. purpurea showed regulation in its N:P ratio. We deposited a wide range of N:P ratios in pitchers, ranging from 0.22 to 56, however at the end of 11 weeks, when we analyzed the fluid we found that N:P ratios converged to an average of 7.3. We found plant tissue of S. purpurea to be static in N content in response to elevated N being deposited in fluid each week. Conversely, we found plant tissue TP to be plastic in response. When we deposited elevated levels of TP in pitcher fluid, we found elevated TP in plant tissue. Biomass of pitchers was greatest at an N:P ratio of 14. From experimental manipulation, we determined a positive correlation between the observed TP of pitcher fluid with Sarraceniopus gibsoni (mite) and Wyeomyia smithii (mosquito) larvae abundance. We observed strong positive correlations between the base of the ecosystem (prey) and fluid stoichiometry, as well as with prey abundance and overall invertebrate abundance. pH was also negatively correlated with the amount of TN that was deposited into the system.