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Marine & Envir Bio Seminar--Dr. Kathleen Ruttenberg
Tuesday, March 20, 2018 12pm to 1pm
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3616 Trousdale Parkway, Los Angeles, CA 90089
Dissolved organic phosphorus composition and bioavailability in natural waters: New insights from new methods
The critical role of Dissolved Organic Phosphorus (DOP) in supporting primary production has motivated efforts to characterize its composition inorder to gain insight into DOP bioavailability and cycling within aquatic systems. This has proven to be an analytically challenging endeavor. As aconsequence, the DOP pool remains poorly characterized, and our predictive power relative to DOP-bioavailability remains poor. While 31P-NuclearMagnetic Resonance spectroscopy (31P-NMR) represents the current state-of-the-art for gaining compositional information on DOP in natural waters, it provides information only on P-bond type, which is inadequate to evaluate DOP bioavailability. Knowledge of the size and molecularcomposition of DOP, beyond P- bonding type, is crucial to evaluating potential DOP-bioavailability. This becomes evident when one considers that DOP bioavailability is contingent upon enzyme cleavage of phosphate from DOP; the size and structure of particular DOP molecules will render them variably accessible to enzyme attack.
A newly developed sequential ultrafiltration (SUF) method provides a new windowinto DOP molecular weight and composition. The SUF methodquantitatively segregates and concentrates DOP into 4 molecular weight size classes, which subsequently can be subjected to bioavailability assaysusing phosphohydrolytic enzymes. Application of this method to a depth profile at the HOT site in the oligotrophic North Pacific Subtropical Gyre, and toa coastal transect of surface waters in Kane'ohe Bay, Hawai'i, reveals substantial variability in DOP molecular weight distribution and bioavailabilitywithin and between sampling sites. These results are in stark contrast to 31P-NMR data from the same or similar sites, which have been used to suggestthat the marine DOP pool is compositionally invariant. Data generated using the coupled SUF-Bioavailability approach clearly show that thecomposition of the marine DOP pool is highly variable in space and time.
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