Variable Light Illuminates The Distribution Of Picophytoplankton

Tiny photosynthetic plankton less than a millionth of a millimeter in
diameter numerically dominate marine phytoplankton. Their photosynthesis
uses
light to drive carbon dioxide uptake, fueling the marine food web over
vast areas of the oceans. A new study published in this week's PLoS ONE by
post-doctoral researcher Dr Christophe Six and a team of scientists from
Mount Allison University, Sackville, New Brunswick, Canada, illuminates
how
the environment regulates the distributions of these ecologically
important species.



Dr Doug Campbell, Canadian Research Chair in Environmental Processes and
co-author explains, "Phytoplankton are entrained in the water column and
are
thus subject to rapid changes in light as they mix through the upper layer
of the ocean."



Dr Christophe Six adds, "Phytoplankton need light for photosynthesis and
survival, but surprisingly this light also inactivates a key component of
the photosynthetic apparatus, photosystem II. This Photoinactivation of
photosystem II decreases photosynthesis and can even kill cells, unless
they
can counteract the damage through repair, which requires nutrients."



"We found the picophytoplankton species isolated from different regions of
the ocean have different abilities for this repair, and therefore have
different abilities to tolerate increases in light. Their repair
capacities are consistent with the different light and nutrient regimes in
their
local environments; species from deep ocean regions with stable light and
low nutrients have very limited repair capacity, but species from coastal
regions with more variable light and higher nutrients are more able to
cope with variable light through rapid repair."



This result indicates that picophytoplankton species' tolerance of
exposures to high light can help to explain how these organisms are
distributed
throughout the ocean. The group measures the rates of photoinactivation
and the rates of the counteracting repair in a wide variety of
phytoplankton
species, and next plans to contribute to ocean models to predict
phytoplankton carbon cycling in response to future climate change.





Citation: Six C, Finkel ZV, Irwin AJ, Campbell DA (2007) Light Variability
Illuminates Niche-Partitioning among Marine Picocyanobacteria. PLoS ONE
2(12): e1341. doi:10.1371/journal.pone.0001341

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