The Hostess with the Mostest: the Effects of Host Tree Leaf Feeding and Light Exposure on Bromeliad Tank pH
Authors:Gretchen North, Kristen Treat
Mentor:Gretchen North, Professor, Biology, Occidental College
Tank bromeliads, flowering plants from the family Bromeliacae, hold water and nutrients in their tanks created by the circular organization of their leaves. The unique aquatic environments formed in these tanks sustain entire microcosms of microscopic life as well as larger organisms. The pH of the water in bromeliad tanks is usually between 4 and 7, but it is not yet clear what exactly determines the pH of a tank. Most species of tank bromeliads are epiphytes that grow on the branches of host trees, thus it is possible that the type of host tree litter collected in the tank and the amount of light the tank is exposed to in the canopy have significant influences on the pH of the tank contents. In this study, I examined the effects of the feeding of different host tree leaves and various levels of light exposure on the tank pH of the widespread bromeliad Aechmea nudicaulis. In a leaf-feeding experiment, plants were collected and separated into groups determined by which type of host leaf was put into their tanks. To test the influence of light, another group was placed in a shade gradient containing high light and low light environments. I predicted that tanks fed with different host tree leaves, as well as tanks exposed to different light environments, would have varying pH values. My results show that there does appear to be a correlation between pH and type of host tree leaf fed and between pH and light level, suggesting that host tree leaf litter and light exposure may both be defining factors of bromeliad tank pH. Knowing more about what affects the pH of bromeliads could lead to further investigation into the intricate metabolic processes and microbial interactions of their tank environments.