Mechanism of Light Acclimation in Marine Phytoplankton

Uriel AparicioDr. Allen Milligan

Relevance50% 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

BackgroundFluorescence 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

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

BackgroundGlobal 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

φ

iPAR