Thar She Blows: of Saharan Dust and Marine Productivity

By Charlie Whittaker

The Sahara Desert is not something you would usually associate with abundant life and vibrant algal blooms. It is one of the most arid and inhospitable areas in the world, representing the largest subtropical hot desert on the planet. And at well over 9,400,000 square kilometres- i.e. about the size of the United States, it is perhaps one of the most inhospitable areas globally. To say that it is unwelcoming to life is an understatement of epic proportions.

The Sahara Desert (credit mtsrs)

The Sahara Desert (credit mtsrs)

However, the desert is in fact one of the cornerstones of continued survival of one of the most abundant groups of organisms on the planet: the phytoplankton. This vast swathe of barren land is actually responsible for a dazzlingly complex and diverse ecosystem albeit thousands of miles away.

Tiny flecks of sand, red in colour due to the abundance of the element iron, are picked up the winds floating across the sand dunes, and in turn, carried thousands of miles westwards on the air currents. These tiny grains of iron rich sand then land in the ocean off the West coast of Africa, where they are responsible for sustaining a astounding array of life. Though individually insignificant and of little relevance, the sheer scale of their deposition makes them a globally relevant input- it is estimated that something in the region of 1015g/year get deposited courtesy of these Saharan winds Westwards. That’s 1012kg, or 1 billion tonnes!

A phytoplankton bloom in the Southern Ocean (credit ESA)

A phytoplankton bloom in the Southern Ocean (credit ESA)

But why all the fuss about iron though? Iron represents a fundamental micronutrient required as a cofactor for the enzymes of a ubiquitous number of different phytoplankton, from cyanobacteria to coccolithophores and diatoms to dizaotrophs. In particular, iron acts as an essential constituent of the enzyme nitrogenase, responsible for the fixation of atmospheric nitrogen. The photosynthetic organisms present in this group are globally significant in terms of the fixation of carbon dioxide from the atmosphere. These so called “forests of the ocean” contribute as much to the control of CO2 levels as tropical rainforests.

Given their dependence on iron then, there has been considerable interest in the concept of “iron seeding” the oceans as a means of generating blooms of these photosynthetic organisms. Such a sudden population rise would lead to increased CO2 drawdown and may have the potential to mitigate, at least in part, some of the consequences of continual anthropogenic mediated CO2 release into the atmosphere. Efforts doing this are still in progress but who would have thought the Sahara Desert, byword for desolate, bleak and lifeless, may have acted as the inspiration for one of the most ambitious biogeoengineering projects currently underway.

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Unbe-leaf-able: Why I don’t back this artificial photosynthesis project, yet.

by Toby McMaster

Silk Leaf, an artificial leaf made from chloroplasts and proteins extracted from silk, is the latest in a series of attempts to mimic photosynthesis. Julian Melchiorri, working with a lab at Tufts University, recently unveiled a synthetic leaf, designed to help humans colonise other worlds by providing us with much needed oxygen. Yet not everything is running as smoothly as it first seems.

The ability to recreate leaves sounds fantastic, so what’s the hitch? Well for a start it only pays up half of what it should, it duly takes in water and Carbon Dioxide, and uses light energy, but currently only reliably produces oxygen. There is no glucose and no one is really sure where the Carbon Dioxide goes. This doesn’t initially sound too bad for us: after all, assuming these things are inedible, we only need the oxygen. However if these leaves were ever to become part of a fully functional plant, these plants would need some kind of energy source. They would need glucose.

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Another obstacle lies in the physical connection of these currently isolated leaves to produce an entire plant. The xylem and phloem inside a plant’s stem, akin to the blood vessels in animals, are complex structures and at best it is naïve to think we can just stick our artificial leaves on and hope they’ll co-operate.

Finally there is currently no data (as far as I can find) on the environmental cost of producing these leaves, which is clearly a key factor in whether they are viable for a trial run on earth, before they can get anywhere near space.

However this project still has a lot of promise. It’s a step in the right direction, and the leaves actually look like leaves, which means their surface area properties are likely to be good. Moreover the fact they look like real plant bits can only help with public acceptance of them, if we ever reach that stage. This might sound like an attempt to simply come up with something nice to say, but it really is important –GM crops, vaccines and nanotechnology are examples of areas which could do a lot more for human kind if not limited by public scepticism.

Scepticism is healthy. It’s why I’m not proclaiming this project as the next big thing in science. There’s a limit though, change is scary, but sometimes it’s necessary. Scepticism without rational basis can hinder progress. Perhaps one day this leaf will help the sceptics see the light when it comes to artificial biology.

The Little Fungus that Could

By Nathan Smith

Deep in the dark depths of fungal taxonomy there lies a phyla known as the Glomeromycota. Members of this phyla are all obligate symbiotes, unable to support themselves independently and requiring a photosynthetic partner to provide organic carbon to them in return for gifts of phosphorous and nitrogen. For all bar one, this photosynthetic partner is a terrestrial plant; the symbiosis being better known as Arbuscular Mycorrhization and which upwards of 80% of angiosperms (flowering plants) are capable of engaging in.

The exception to this Golden Rule of the Phyla? A species known as Geosiphon pyriformis which instead forms a relationship with the cyanobacteria, specifically the species Nostoc punctiforme.

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Geosiphon:Nostoc symbiosis; Geosiphon spores inset
(credit Schuessler Lab)

The Geosiphon:Nostoc symbiosis appears to be unique in nature as the only example of an endosymbiosis between a fungus and a bacteria.  Adding to its mystery, it has so far been reported to have been found only 6 times in the wild in a small region of eastern Germany and Austria.

In contrast to Arbuscular Mycorrhization, where the fungal partner invades the cells of the plant to create an exchange interface, the cyanobacteria are taken in by the fungi, surrounding them with a unicellular structure known as a ‘bladder’ that can grow up to 2mm in length.

The exchange of nutrients is also different than in Arbuscular Mycorrhization. With the exception of nitrogen and carbon, all of the cyanobacteria’s nutritional needs must be met by the fungus. In return, the fungus receives organic carbon and nitrogen.

It is possible that Geosiphon:Nostoc symbiosis represents an important step in fungi being able to form symbiotic relationships with plants; it’s also possible that the Geosiphon:Nostoc developed out of the wider spread Arbuscular Mycorrhiza symbioses.

Either way it’s an interesting story of one fungus breaking the mould.

Invisible forests; and how marine dwelling microorganisms really rule the waves!

By Charlie Whittaker

For sure, the abundance of terrestrial plants we share our planet with are weird and wonderful in equal measure, but why should they get all the glory when there’s an equally as important component to the biomass on Earth? I’m of course talking about the much maligned, often overlooked, and most definitely misunderstood microscopic creatures that inhabit the murky depths of our oceans!

The marine environment is by far the planet’s largest habitat. Covering over 70% of the land area, it contains a huge diversity of organisms, co-existing in a harmonious, yet fragile, balance. Underpinning all the life that the oceans sustain are photosynthetic organisms. Tiny, often microscopic and unicellular, these organisms are responsible for roughly half of all the primary productivity of the planet. Their ability to capture sunlight and use it to synthesise new organic compounds provides the energy for the diversity of marine life found in the ocean. They are, for want of a better analogy, the oceans’ invisible forest.

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These primary producers are exceptionally diverse, ranging from tiny photosynthetic bacteria that hitch a ride on the tiny particulate matter found in seawater, to the phytoplankton. These represent a hugely diverse group of unicellular organisms. Contained within this group are the diatoms, which enclose their cell in a glass box made out of silica, as well as the dinoflagellates, that tend to employ semi-opaque plates of cellulose to separate themselves from the external environment. And then who could forget the coccolithophores? Unicellular like their other phytoplankton counterparts, these microorganisms cover themselves with ornamented plates called coccoliths made out of calcium carbonate.

So why does any of this matter?

80 million tonnes of marine seafood are caught globally each year. Seafood forms a common constituent of diets worldwide and provides more than 1.5 billion people with at least 15% of their protein requirements. The entirety of this marine life, whether directly (animals that feed on the producers themselves) or indirectly (in the case of organisms several trophic levels above the primary producers), relies upon the productivity and photosynthesis these organisms are carrying out.

They also represent an important carbon sink. The ocean plays a huge role in mopping up and buffering CO2 released into the atmosphere: and a significant proportion of the ability to do this stems from the simply huge amount of photosynthetically capable biomass present.

Okay, that’s fine and dandy then?

Not quite. Unfortunately things are getting progressively less peachy. Climate change poses a serious issue to the future productivity of the oceans and marine life. Changes to the oceanic average temperature has implications ranging from alterations to the vertical stratification of the water column (important in mixing, thereby ensuring all the phytoplankton receive all the nutrients they need) to impacting the chemical reactions responsible for the productivity of the primary producers. Whilst of course, the response to rising sea temperatures will not be the same globally (a paper recently published in nature showed that “Some phytoplankton like it hot” and that warming oceans may increase productivity in some areas) there are important marine areas of human concern that are set to suffer substantially: the Atlantic Cod population has plummeted in number in recent years. Partly this has been driven by overfishing, but it was also shown this was due to rising temperatures. The alteration modified and impacted the plankton ecosystem in such a way that it reduced the survival rates of young cod, and thereby facilitated the population’s rapid decline.

They may be invisible, but the effects of these tiny photosynthetic powerhouses are quite the opposite. And unless something is done soon, they may be at the forefront of drastic alterations to our current marine system.

Further reading:

On the effect of increased temperatures on cod and phytoplankton populations.

On the propensity some phytoplankton show for warmer temperatures.

Marine Biology: A Very Short Introduction.

You’ve got the wrong (fun)guy!

by Nathan Smith

If you were presented with a plant and a fungus and asked to pick the parasite, chances are you’d pick the fungus. Whilst this is often the case, there are significant and widespread cases of the relationship being the other way around. Enter Orchids.

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Common Spotted Orchid

Orchids are family of plants distinct in physical appearance and are renowned for their sweet scent and aesthetic beauty, despite the fact they more closely related to rice than they are to roses. Their seeds contain rather small reserves of nutrients and they are unable to photosynthesise immediately after germination, instead going through an achlorophyllic stage; in fact some orchids are not capable of photosynthesis during their lifespan. Usually small reserves and an initial inability to photosynthesise would be considered a bad strategy for a plant, but Orchids are still thriving and there is a good reason why.

Throughout their non-photosynthesising stage, and indeed throughout their entire existence, they are the dominant partners in what can best be described as an uneven symbiotic relationship with a fungal partner.  In fact, a fungal partner is required by the orchid for them to germinate ‘in the wild’. Orchids can be germinated in sterile conditions; however this requires exposure to the ‘fungal sugar’ trehalose.  So what is the trade between the orchid and the fungus?  The fungus supplies the plant with organic carbon, a source of nitrogen, phosphorous, and other minerals and nutrients, and in return, gets… well, not much really. This uneven relationship continues once the plant gains the ability to photosynthesise and there is little evidence that the fungus gains a significant amount of reduced carbon from its photosynthetic symbiont. The fact that the fungus enters into a symbiosis with the plant in the first place, and continues this relationship throughout the plant’s life, suggests the fungus gains something from the relationship or that the plant emits a strong attractant, however there is little to no evidence for this and so these hypothesises remain little more than speculation.

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Tway-blade Orchid

What about the orchids that never photosynthesise? These plants, for instance the Bird’s-nest Orchid, have a habit of forming symbioses with fungi that also associate with tree roots. This allows them to use the fungus like a straw and indirectly parasitise what they need from the unsuspecting trees. Clever stuff.

Orchids are beautiful and interesting plants and deserve to be admired, but it doesn’t mean it’s the good guy. Next time spare a thought for the poor little fungus.

Photography by Leanne Massie

Super-domestication: making plants work for us

by Leanne Massie

Super-domestication is a relatively new term to describe plants that we have modified to extremes to fit our own needs. For example, crops that have huge yields with minimal negative effects on the environment could be called super-domesticates.

These crops are still works in progress though; the most notable super-domesticate-to-be is “C4 rice”. Rice is naturally a C3 plant, which means it uses a less efficient method to capture carbon from the atmosphere. Some plants that are adapted to hot, dry conditions have evolved a different carbon capture mechanism called C4 photosynthesis, which allows them to take up more carbon dioxide and lose less water in the process, a sort of supercharged version of photosynthesis. If C4 photosynthesis could be introduced into rice the benefits are staggeringly huge. Yields would be increased while at the same time water use would go down. In a world where water shortages are starting to affect everyone and where rice already provides more than one fifth of the total calories consumed worldwide, a C4 variety of rice would go a long way to ending world hunger.

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Credit: Dalgial

This isn’t an easy process though; introducing C4 into a C3 plant is like trying to compare pricing at a supermarket, extremely difficult!. It can be done but takes huge amounts of effort and determination.  But fortunately, C4 photosynthesis has evolved more than 50 times in nature so with the right tools it is very feasible. The C4 Rice Consortium, a foundation that has more than 600 scientists worldwide, has been working on introducing C4 photosynthesis into rice since 2008 and the researchers have collectively published over 400 papers relating to C4 rice since. The scientists are well on their way to making rice into a super-domesticate.

However, this is only rice. Wheat, corn, potatoes, tomatoes, and peas are just some of the other crops that are also being studied to make them work harder for us. Imagine the possibilities that super-domestication could bring if all our crops were supercharged to their full potential.

For more information, see:

C4 Rice Project. http://c4rice.irri.org

D.A. Vaughan, E. Balazs, J. S. Heslop-Harrison (2007) From Crop Domestication to Super-domestication. Annals of Botany 100: 893-901