Event Title

Bridging the Gaps in Freshwater Silicate Cycles: Assessing Silicate Demand and Incorporation in Freshwater Phytoplankton

Mentor 1

Erica Young

Mentor 2

John Berges

Location

Union Wisconsin Room

Start Date

5-4-2019 1:30 PM

End Date

5-4-2019 3:30 PM

Description

Silicate (Si) is a potentially limiting nutrient, shaping the community structure of phytoplankton – the base of most freshwater food webs. The silicate cycle has been well studied in marine ecosystems, but is relatively poorly characterized in freshwater ecosystems, such as the Laurentian Great Lakes. Dissolved silicate concentrations in Lake Michigan have increased over the past 3 decades, which may be related to declines in Si-requiring phytoplankton such as diatoms. However, the mechanisms behind this remain unclear, as the increase appears to be too great to be due to diatoms alone. To better understand Si dynamics in lake ecosystems, the silicate demand and use by diverse freshwater phytoplankton taxa, including known Si-requiring taxa such as diatoms and chrysophytes as well as non-siliceous species, must be examined. Our experiments aimed to characterize growth rates (measured as change in chlorophyll a fluorescence) and Si incorporation into biogenic silicate (bSi) of the diatom Cyclotella meneghiniana, the green alga Chlamydomonas reinhardtii, and the chrysophyte Chrysocapsa sp. Cells were cultured with full-Si growth media, Si-free media, and full-Si media with the addition of Germanium dioxide (+GeO2), an inhibitor of Si incorporation. The diatom C. meneghiniana showed significantly decreased growth in both Si-free and +GeO2 treatments (n=3, p<0.01). Biogenic silicate analyses showed significantly higher bSi in the full Si treatment (n=3, p<0.01). Significant growth decreases were also seen for +GeO2 treatments for the chrysophyte Chrysocapsa (n=3, p<0.01) and the green alga C. reinhardtii (n=3, p<0.05). However, there were no significant differences in bSi, with both species having much lower bSi than C. meneghiniana. Fluorescence microscopy of cells exposed to a bSi-indicating fluorochrome, PDMPO, also showed bSi incorporation present only in C. meneghiniana. Experiments to quantify bSi incorporation rates using PDMPO and fluorescence spectroscopy in C. meneghiniana are currently underway.

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Apr 5th, 1:30 PM Apr 5th, 3:30 PM

Bridging the Gaps in Freshwater Silicate Cycles: Assessing Silicate Demand and Incorporation in Freshwater Phytoplankton

Union Wisconsin Room

Silicate (Si) is a potentially limiting nutrient, shaping the community structure of phytoplankton – the base of most freshwater food webs. The silicate cycle has been well studied in marine ecosystems, but is relatively poorly characterized in freshwater ecosystems, such as the Laurentian Great Lakes. Dissolved silicate concentrations in Lake Michigan have increased over the past 3 decades, which may be related to declines in Si-requiring phytoplankton such as diatoms. However, the mechanisms behind this remain unclear, as the increase appears to be too great to be due to diatoms alone. To better understand Si dynamics in lake ecosystems, the silicate demand and use by diverse freshwater phytoplankton taxa, including known Si-requiring taxa such as diatoms and chrysophytes as well as non-siliceous species, must be examined. Our experiments aimed to characterize growth rates (measured as change in chlorophyll a fluorescence) and Si incorporation into biogenic silicate (bSi) of the diatom Cyclotella meneghiniana, the green alga Chlamydomonas reinhardtii, and the chrysophyte Chrysocapsa sp. Cells were cultured with full-Si growth media, Si-free media, and full-Si media with the addition of Germanium dioxide (+GeO2), an inhibitor of Si incorporation. The diatom C. meneghiniana showed significantly decreased growth in both Si-free and +GeO2 treatments (n=3, p<0.01). Biogenic silicate analyses showed significantly higher bSi in the full Si treatment (n=3, p<0.01). Significant growth decreases were also seen for +GeO2 treatments for the chrysophyte Chrysocapsa (n=3, p<0.01) and the green alga C. reinhardtii (n=3, p<0.05). However, there were no significant differences in bSi, with both species having much lower bSi than C. meneghiniana. Fluorescence microscopy of cells exposed to a bSi-indicating fluorochrome, PDMPO, also showed bSi incorporation present only in C. meneghiniana. Experiments to quantify bSi incorporation rates using PDMPO and fluorescence spectroscopy in C. meneghiniana are currently underway.