State Changes in the Sarracenia purpurea Microecosystem
Sarracenia purpurea, or the Northern Pitcher Plant, is a long-lived, perennial, carnivorous plant found in nutrient-poor bogs and fens across North America and Canada. The plant forms pitchers from modified leaves which fill with rain water and recruit a multi-trophic food web that includes bacteria, rotifers, protozoa, and insect larvae. This food web is responsible for breaking down, decomposing, and mineralizing the insect prey that falls into the pitchers. The mineralized nutrients and carbon dioxide released through decomposition of prey can be taken up and used by the plant.
The S. purpurea system experiences a rapid change if pitchers are enriched with organic matter at a high enough concentration and rate. The addition of organic matter causes an increase in oxygen demand by bacteria, resulting in a rapid crash in the concentration of dissolved oxygen inside the pitchers. This change is similar to changes that occur in larger aquatic systems. In lakes and ponds, enrichment of phosphorous can cause a rapid decline in water clarity, resulting in the death of primary producers. These primary producers then fall to the bottom and are decomposed by bacteria, increasing oxygen demand and depleting dissolved oxygen. Though the brown food web in S. purpurea is detritus-based and the green food web in lakes and ponds is primary producer-based, both ecosystems experience increases in detrital load and subsequent decline in dissolved oxygen. In lakes and ponds, these state changes lead to changes in the food web, such as a loss of higher trophic levels, and state changes represent shifts between alternative stable states. Though the S. purpurea ecosystem experiences a rapid state change, it is not clear if there are alternative stable states and the impact of the state change on higher trophic levels is unknown.
I am interested in whether or not organic matter loading causes shifts between alternative stable states in the S. purpurea ecosystem. I use a mix of controlled greenhouse and field experiments to explore the dynamics of state changes in the S. purpurea system. Specifically, I am interested if the shift between alternate states in the system displays hysteresis.
Microbial Protein Expression During a State Change in S. purpurea
State changes between stable states in aquatic ecosystems can happen suddenly and are difficult or impossible to reverse. They are often accompanied by undesirable changes, such as increased algal cover and decreased water clarity. Researchers are particularly interested in predicting state changes so that they can be prevented, but the best predictors of state changes may not give enough lead-time for successful mitigation.
Changes in decomposition rates in response to organic matter enrichment should be accompanied by changes in the expression of microbial proteins and pathways involved in decomposition. As decomposition rates increase and dissolved oxygen is used up, there should also be resulting changes in pathways associated with microbial respiration and decomposition, as well as changes in the abundance of stress response proteins. Such changes in protein expression could provide useful biomarkers for predicting state changes if they occur before changes in statistical parameters that serve as traditional indicators.
Part of my research focuses on using metaproteomics to characterize the metaproteome of the microbial community in the S. purpurea system as it undergoes a state change. Further, I hope to identify a few proteins that reliably change in abundance as a state change occurs that could be useful biomarkers for predicting state changes.