Mechanism of Light Acclimation in Marine Phytoplankton Uriel Aparicio Dr. Allen Milligan

Relevance 50% of net photosynthesis of the earth comes from marine phytoplankton. Primary production is sensitive to climate variability To understand these changes and to be able to predict future changes we need to understand factors that influences phytoplankton growth. Example: limiting nutrients

Background Fluorescence can be used to indicate physiological status of the phytoplankton. example: high fluorescence=iron limited phytoplankton In 2002, NASA launched its AQUA satellite with MODIS (MODerate-resolution Imaging Spectroradiometer). MODIS is an instrument that can measure the fluorescence of marine phytoplankton.

Background Fluor

Absorb Light~Incident Light Fluor~Absorbed Light?

NO! Fluorescence saturates

Why?

Energy is being lost to some other pathway

Energy Pathways Photochemistry Fluorescence Non-Photochemical quenching (NPQ)

Light availability and nutrient stress can have an effect on the fluorescence through NPQ Low light acclimated cells have more chlorophyll than high light acclimated cells and therefore absorb more energy. (Greater NPQ) To detect nutrient stress, fluorescence must be corrected for light dependent NPQ response So far the corrections to fluorescence data have assumed a single photoacclimation state

Objective Test NPQ response of phytoplankton under different light conditions

Hypothesis Low light acclimated cells will demonstrate a stronger NPQ response than the high light acclimated cell. Low light acclimated cells have more chlorophyll and therefore absorb more energy when they are at the surface.

Methodology

Measure the natural fluorescence Measure the NPQ

Fluorescence Yield High acclimated cells have a greater fluorescence yield than the low acclimated cells.

NPQ Measurements (Fm- Fm’)/Fm’ Averaged the last 4 data points

Results Low Light Acclimated NPQ: 0.69 High Light Acclimated NPQ: 0.35

Prior research has concluded the opposite of our research (Garcia-Mendoza and Colombo-Pallotta 2007; Niyogi et al. 1997a) These studies (and others) acclimated their organisms to high and low constant light

Maps derived from Satellite Data

Acknowledgements Howard Hughes Medical Institute NASA Dr. Allen Milligan Dr. Michael Behrenfeld Dr. Kevin Ahern

Background Global climate change can change the availability of nutrients that are limiting in the ocean Previous studies have been done on iron limitation in the ocean but are limited to bottles or iron addition to surface water. New techniques with satellites can cover the entire ocean by measuring fluorescence of phytoplankton. The amount of fluorescence emitted indicates the physiological state of the phytoplankton

Hypothesis A. NPQ is perfectly efficient at dissipating light energy B. Fluorescence yield is dependent on the ratio of PSII : PSI C. Fluorescence yield is dependent on the photoacclimation state  iPAR