UVM Theses and Dissertations
Format:
Print
Author:
Wakefield, Amy E.
Dept./Program:
Biology
Year:
2004
Degree:
M.S.
Abstract:
The carnivorous pitcher plant Sarracenia purpurea, which has developed adaptations to capture prey for supplemental nutrients, may be sensitive to changes in the quantity of prey available. Using a controlled field experiment, I examined the effects of nutrient addition in the form of elevated prey on the morphology, photosynthetic rate, and nutrient content of the leaves of S. purpurea. We conducted this experiment in Belvidere Bog, Vermont, over a three-month growing season with eight levels of prey addition: 0 to 7 house flies were added to 200 S. purpurea twice-weekly. Five plants from each treatment group were selected for harvests at 17-day intervals and removed from the experiment on the date of the harvest. Morphology was measured as the size and length of the pitcher and keel, as well as the weight and number of pitchers on each plant. In addition, we measured the photosynthetic rate (mmol/m²/s²CO₂) in the field and nutrient content of the water contained within the pitcher and of the pitcher leaf tissue in the lab. I used a multivariate analysis of variance to determine whether there was a difference in morphology and nutrient level among treatments and harvests, followed by two-way analysis of variance on each response variable to determine the effect of treatment level and harvest date.
The addition of soluble N to the pitcher leaf reduces the tube diameter and keel size of the leaf (Ellison and Gotelli 2002). I tested the hypothesis that the same effect would occur with supplemental prey. There was no difference in morphology between treatment levels or harvest date, however, nor was there an increase in the number of pitchers with additional flies. Although a cost/benefit model of carnivory predicts that the rate of photosynthesis will increase with higher nutrient absorption (Givnish et. at 1984), my results show that there was no difference in the photosynthetic rate between treatments. While the pH of the pitcher water remained constant with fly treatment level and harvest date, the dissolved oxygen content of the water decreased with treatment, which could affect the decomposers within the pitcher as well as the uptake of nutrients by the pitcher tissue. While NO₃ and PO₄ levels within the pitcher water were not significantly different between treatment levels or harvests, NH₄ levels increased with treatment. The concentration of N and P in the pitcher tissue increased with the addition of prey. The ratio of N:P in the tissue also suggests that P is the primary limiting nutrient for control plants, which may reflect excess contributions of anthropogenic N.
The addition of soluble N to the pitcher leaf reduces the tube diameter and keel size of the leaf (Ellison and Gotelli 2002). I tested the hypothesis that the same effect would occur with supplemental prey. There was no difference in morphology between treatment levels or harvest date, however, nor was there an increase in the number of pitchers with additional flies. Although a cost/benefit model of carnivory predicts that the rate of photosynthesis will increase with higher nutrient absorption (Givnish et. at 1984), my results show that there was no difference in the photosynthetic rate between treatments. While the pH of the pitcher water remained constant with fly treatment level and harvest date, the dissolved oxygen content of the water decreased with treatment, which could affect the decomposers within the pitcher as well as the uptake of nutrients by the pitcher tissue. While NO₃ and PO₄ levels within the pitcher water were not significantly different between treatment levels or harvests, NH₄ levels increased with treatment. The concentration of N and P in the pitcher tissue increased with the addition of prey. The ratio of N:P in the tissue also suggests that P is the primary limiting nutrient for control plants, which may reflect excess contributions of anthropogenic N.