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Kathleen Pryer

Kathleen Pryer

KATHLEEN PRYER

This lowly fern has massive green potential Add to ...

Kathleen Pryer is professor of biology at Duke University and president of the American Fern Society.

Fifty million years ago, the Earth was so warm that turtles and alligators thrived in lush forests at the poles. Much of the North Pole was covered in a rather less charismatic life form: the floating, duckweed-like azolla fern.

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Recent geological evidence from Arctic Ocean seabeds reveals 50-million-year-old sediments that are composed almost entirely of azolla fossils for an 800,000-year span. This interval, known as the “Arctic azolla event,” was a period when the azolla repeatedly blanketed the ocean surface, forming dense mats of vegetation.

Then something really interesting happened. As these plants died and became part of the sediment, they took atmospheric carbon down with them. Global atmospheric levels of carbon dioxide fell significantly, precipitating Earth’s initial shift from a greenhouse world toward the current icehouse climate that we’re now worried will melt.

Azolla is still with us, floating on the surface of ponds, lakes and rice paddies. While tiny – one azolla plant could comfortably sit on top of your smallest fingernail – it can double its entire body mass in less than two days. Some researchers think this makes it a promising alternative for biofuel production and carbon-capture efforts.

But azolla does yet another interesting trick: It captures all the nitrogen fertilizer it needs from the atmosphere around it. Since the dawn of agriculture, Asia’s farmers have known about, and deliberately exploited, the benefits of growing azolla as a companion plant with rice. The floating fern thrives in rice paddies, fixing nitrogen and other nutrients, constantly improving the soil composition and providing a natural, green fertilizer that significantly bolsters rice productivity.

The secret here is that azolla isn’t just a plant; it’s a “superorganism,” a symbiotic collaboration of a plant and a microbe. In a special protective cavity inside each leaf, azolla hosts a microbe called nostoc that spends its entire life converting atmospheric nitrogen into food for its host.

Azolla and nostoc have clearly demonstrated a prodigious ability to combat global warming, and to produce precious nitrogen that could help feed the world in a more sustainable way. Even though they have been co-evolving for nearly 100 million years, we know very little about them and how they communicate. Wouldn’t it be great to understand this symbiotic relationship better, and to be able to understand the biological “conversation” between the host and the microbe?

Because it is classified as a “lowly fern,” azolla has been sidelined in plant genome studies. Repeated appeals to granting agencies for funding to unlock the know-how embodied by this superorganism have been met with responses like “too unconventional” or “too risky.”

But to sustainably produce food for a world population of more than seven billion people – all while reducing pollution and greenhouse gases – we need to do some risky research. Novel ideas and innovative approaches that could reveal just how nature “does what it does” naturally might help to revolutionize current farming practices. The cost of continuing to do the same old, same old makes little economic sense.

Specifically, we need a more sustainable source of nitrogen. By 2015, roughly 200 million tons of industrially produced, nitrogen-rich fertilizer will be needed to grow the world’s food, a process that will consume vast amounts of fossil fuel and exacerbate our carbon dioxide problems.

Azolla and nostoc have great potential to reduce the world’s reliance on fossil fuels, while scrubbing a bunch of carbon out of the atmosphere in the bargain.

We’re not talking about a lot of money to do this. Genomic sequencing of this unique azolla-nostoc system would cost well under $1-million (U.S.). That’s far less than the yearly billions that North American farmers pay for nitrogen fertilizer – much of which finds its way into rivers and streams, damaging delicate water systems. This small step toward potentially helping crops to use less synthetic nitrogen could benefit farmers’ bottom lines, the environment and the prices we pay for food.

I’d like to see the genome of the azolla superorganism sequenced so that we can understand the language that codes for the molecular machinery underlying this symbiotic partnership, and possibly tailor it to suit our needs. Knowing how this works might even enable us to engineer crops to fix their own nitrogen – an achievement that could truly revolutionize modern agriculture.

Not often does such a small price promise such a big gain.

 

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