Effect of Temperature on Extracellular Polymeric Substance Production (EPS) by Diatoms

Texas A&M Research Foundation, College Station TX

Investigators

Abstract

It is necessary to determine the fate of organic matter in the ocean to understand marine food webs, biogeochemical cycles, and climate change. Diatoms fix approximately a quarter of the net global primary production each year, and a significant proportion of this production is excreted as extracellular polymeric substances (EPS). EPS have a profound impact on pelagic ecosystems by affecting the formation of aggregates. Diatoms and other particulate organic carbon (POC) sink rapidly as aggregates, affecting the biological carbon pump, which plays a pivotal role in the sequestration of carbon in the ocean. The proposed research will test the central hypothesis: Temperature increase affects diatom release of EPS, which act as a glue, increasing aggregation. Previous work by the investigator showed that increased temperatures affected the aggregation of Skeletonema costatum. Four specific hypotheses will be tested: H1: Diatoms produce more EPS with increasing temperature. H2: Diatoms produce more transparent exopolymer particles (TEP) with increasing temperature. H3: The quantity or composition of cell-surface carbohydrates in diatoms changes with temperature. H4: Aggregation of diatom cultures and natural plankton increases with temperature. Laboratory experiments (years 1 - 2) will be conducted with three model diatom species grown at controlled growth rates and defined limitation (nitrogen or light) in continuous culture. Culture temperature will be stepped up or down in small increments to determine the effect of the temperature change on EPS production, aggregation, and partitioning of carbon in intra- and extracellular pools. Similar experiments in year 3 will be carried out using natural plankton populations from a coastal site where diatoms contribute a significant proportion to the biomass. Broader Impacts: The proposed research will increase our understanding of the ecology and physiology of one of the dominant groups of primary producers on Earth. EPS are a central aspect of diatom biology, though the physiology, function and broader ecosystem impacts of EPS production remain unknown. This research will determine how temperature, light limitation, and nutrient limitation affect the partitioning of production between dissolved, gel, and particulate phases in the ocean. Measurements of plankton stickiness (alpha) under different conditions will be important to model aggregation processes in the ocean as alpha is an important (and variable) term in coagulation models. Determining how carbon is cycled between the ocean, atmosphere and lithosphere is key to understanding climate change on both geological and human time scales. This is a major societal issue as atmospheric CO2 concentrations are steadily increasing, correlating with a 0.6C rise in global average temperature during the last century. This research will address potential feedbacks between warming of the surface ocean, diatom ecophysiology and the biological carbon pump. A graduate student will be supported by this program and receive training in microbial ecology and biogeochemistry. Undergraduates from across the Texas A&M University campus will be offered an opportunity for hands on research experience in oceanography. These students will become active partners in the research by conducting individual research projects. Results from the research will primarily be disseminated through peer-reviewed publications and presentations at scientific meetings, with students playing an active role at all stages in the dissemination process.