Jacob J. Grothjan and Erica B. Young
Department of Biological Sciences, UW-Milwaukee, grothjan@uwm.edu, ebyoung@uwm.edu
The pitcher plant Sarracenia purpurea grows in nutrient-deficient wetlands such as Cedarburg Bog and supplements mineral nutrition by carnivory. Newly formed pitchers are sterile, but fill with rainwater, in which insect prey drown. Within the pitcher detrital food web, invertebrates begin macroscopic breakdown of prey while microbial hydrolytic enzymes (chitinases, phosphatases, proteases) digest and release nutrients, prior to absorption by the plant. These microecosystems are the target of trophic food web studies, but more detailed functional analysis of bacteria and eukaryotic taxa are lacking. In order to characterize the pitcher community composition and function, this research addressed three specific questions: What bacteria and eukaryotic organisms are present in the pitchers? How does bacterial succession and hydrolytic enzyme activity develop in Sarracenia purpurea over the lifespan of a pitcher, from opening to senescence? How do possible sources of bacteria (rain, captured prey) affect bacterial abundance and enzyme activity in the community? Pitcher plants in the Cedarburg Bog were sampled in 2013 and 2015; plants were also transplanted from the bog and monitored under greenhouse conditions to control sources of bacteria added to pitchers. Bacteria and eukaryotes were identified using analysis of 16S and 18S rRNA gene sequences, enzyme activities were measured using biochemical assays, and bacterial cell abundance estimated by epifluorescence microscopy. Pitchers harbored diverse bacteria and eukaryotic ciliates, arthropods including springtails and mites, fungi, and protists including green algae. Enzyme activity increased for 2 weeks after pitcher opening and then became variable, with a 145-fold variation in hydrolytic enzyme activity measured in 20 pitchers over the summer. Enzyme activity in field samples may vary in relation to detritus (prey) load in the pitchers, which can increase with pitcher age. In the greenhouse plants, with different bacterial sources, adding prey increased hydrolytic enzyme activity compared with distilled water controls, but there was also a 35-fold variation in hydrolytic enzyme activity measured in 35 pitchers. Pitcher plants harbor a diverse population of bacteria and eukaryotes which play roles in the detrital food web from which the plant host gains nutrients. Ph.D. research, Dr. Erica Young, Major Advisor.