Scientists describe novel strategy for phytoplankton growth in nutrient-poor areas of sea

March 11th, 2009 - 3:48 pm ICT by ANI  

Washington, March 11 (ANI): An international team of scientists has described a novel strategy for phytoplankton growth in the vast nutrient-poor habitats of tropical and subtropical seas.

Until now, it was thought that all cells are surrounded by membranes containing molecules called phospholipids oily compounds that contain phosphorus, as well as other basic elements including carbon and nitrogen.

These phospholipids are fundamental to the structure and function of the cell and for this reason had been thought to be an indispensable component of life.

Phospholipids are one of several classes of molecules that contain the element phosphorus, which has been shown to be in very short supply in many marine ecosystems.

The deep sea contains ample phosphorus, but delivery to the surface waters where photosynthesis occurs is limited by temperature-induced stratification and the inability to mix the ocean to depths where phosphorus is available.

Research conducted at Station ALOHA near Hawaii during the past two decades has shown that phosphorus is rapidly becoming less abundant in the stratified regions of the North Pacific Ocean, possibly a result of changes in the marine habitat due to greenhouse gas warming.

Benjamin Van Mooy of the Woods Hole Oceanographic Institution and colleagues discovered that phytoplankton in the open ocean may be adapting to the low levels of phosphorus by making a fundamental change to their cell structure.

Rather than synthesizing the phosphorus-requiring phospholipids for use in their membranes, the plants appear to be using non-phosphorus containing substitute lipids that use the nearly unlimited element sulfur also found in seawater instead of phosphorus.

These substitute sulfolipids apparently allow the plants to continue to grow and survive under conditions of phosphorus stress, a unique strategy for life in the sea.

To test the generality of this biochemical strategy, the researchers compared the response of the phytoplankton communities in different ocean basins that experience varying levels of phosphorus stress.

In regions where phosphorus stress is extreme, such as the area dubbed the Sargasso Sea in the central North Atlantic Ocean, phospholipids were nearly nonexistent.

By comparison, in the South Pacific Ocean, where sufficient phosphorus exists, there were large amounts of phospholipids.

The region around Hawaii was intermediate, which is consistent with the long-term data sets from the Hawaii Ocean Time-series program showing that phosphorus is still measurable but is disappearing from the surface waters at an alarming rate.

One prediction from this initial study is that the phytoplankton in Hawaiian waters are likely to become more like those in the Sargasso Sea over time as phosphorus supplies dwindle further. (ANI)

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