Phosphorus (P) is a recognized essential nutrient for marine primary production and its inorganic chemistry has been well studied. However, the dissolved organic phosphorus pool (DOP) has been little studied even given its importance as a phosphorus source to microorganisms. This project will identify biogenic sources of P compounds to DOP using controlled culture studies focused on phosphonate and polyphosphate. These compound classes exert important controls over P cycling, carbon fixation and community structure and export from the upper ocean, and long-term sequestration. The study will employ innovative methods, including molecular tools and novel chemical analyses, to examine specific phosphonate and polyphosphate compound production by key phytoplankton taxa under different environmental conditions. Four hypotheses are driving the proposed research and focus the study on the primary research questions. The study will improve our understanding of the production of specific P compounds, and provide insight into the bioavailability of DOP and the influence of P on biological production.
The project will train three graduate students and there is a substantial outreach component associated with the study. The PIs will integrate education and outreach to K-12 communities using Whyville, an online virtual world geared specifically to 8-14 year old children. During this study, the investigators will expand the use of Whyville as a science learning tool through interactions with at-risk children as part of ScienceQuest, an after school program at a housing shelter, and through intensive summer short courses to school teachers.
Phosphorus (P) is an essential nutrient utilized by all organisms for growth and it exists in many chemical forms throughout Earth. In marine systems, P is known to both limit biological production as well as influence food webs. Yet there is still much we do not know regarding the specific chemical structures of P that exist in the natural environment or how chemical structure differences influence P bioavailability to a number of aquatic organisms. Indeed, this lack of knowledge has greatly hindered our understanding of P cycling throughout the hydrosphere. Research has shown that microbial organisms produce a range of dissolved organic P (DOP) compounds in response to their abiotic and biotic environments, yet counter intuitively; measurements suggest that DOP remains surprisingly invariant with depth and region in the ocean. Given the importance of DOP as a P source to microorganisms and the ecosystem implications of DOP utilization, understanding this surprising observation remains a fundamental challenge in marine P biogeochemistry. The major goals of this research were to: 1) Characterize the relative proportions of the major P compound classes produced by several of the most common types of phytoplankton 2) Track how the relative proportions of DOP change under varying conditions of two very common phytoplankton groups. 3) Connect patterns observed in P compound class distributions to P-related gene expression. 4) Compare the diversity in P compounds observed in laboratory studies to that observed in the ocean. This grant has enabled us to develop new tools for examining DOP composition, including a process (electrodialysis/reverse osmosis) that pre-concentrates DOP from large volumes of seawater into much smaller quantities, enabling more detailed and comprehensive analysis. These analyses include the refinement of liquid and solid state 31P nuclear magnetic resonance and the application of new chemical methods that identify specific P compounds. Laboratory and field results suggest that specific compounds within the DOP pool are differentially used by organisms for growth, thereby influencing microbial community composition. Furthermore, specific plankton groups reallocate their P stores to take advantage of future environments that are anticipated to be low in available P. These results are some of the first to provide insight into how DOP availability and composition directly impacts the growth and structure of plankton food webs in both coastal and open ocean environments. In addition to a number of research presentations and submitted and published articles pertaining to this project, we participated in and initiated a number of unique outreach and education activities, including teacher workshops (www.earth2class.org), presentations at marine educator conferences, afterschool programs geared towards at risk students in K-7th grade (www.geol.sc.edu/cbnelson/ScienceWeb/index.htm), and further development of the virtual world, Whyville (www.whyville.net).
