Biofuels might not be that bad after all

By Joanna Wolstenholme

You have heard of the need to find new sources of energy that do not involve fossil fuels. And you have also probably heard of bioethanol from maize and sugar cane, and the scepticism surrounding their green credentials. This scepticism comes with good reason – these sources of biofuels often divert valuable food from the food chain into fuel production, raising the cost of living. This was vividly illustrated by the food crisis in 2007/8, partly caused by America and the EU incentivising the production of bioethanol. So should we write off biofuels altogether?

Simply put – no – not all biofuels. Second generation biofuels are what you should really be talking about. Write off those inefficient first generation biofuels with their ‘food vs fuel’ baggage, but don’t write off biofuels altogether. Lignocellulosic biofuels are the next big thing – the same green pros, but less of the cons. These biofuels can be made from waste products like straw, maize cobs and bagasse (sugar cane straw), and, excitingly, these technologies are just starting to become commercially viable.

Is straw like this the future of biofuels? (Credit Richard Walker)

Is straw like this the future of biofuels? (Credit Richard Walker)

Lignocellulose is found in the plant cell wall, and is the main component in plant biomass. Unlike sugars (which whilst easily accessible for use in first generation biofuels, are only a small portion of the overall biomass), cellulose is generally an unwanted by-product that goes to waste, thanks to how hard it is to break down. However, researchers are finding new enzymes and treatment methods that are able to attack the cellulose in ever more efficient ways. The first commercial plants have already been built in Brazil and Italy, using biofuel crops like Miscanthus that can be grown on marginal or contaminated land (rather than prime agricultural land), or waste products like straw. These take advantage of government subsidies on renewable electricity to help cover the cost of generating the biofuels whilst scientists work to bring these costs down.

In the 1970s Brazil got worried about its oil supply, so started to move the country to bioethanol. The system was heavily subsidised- but now is self-sufficient, and yields have doubled. Lignocellulosic biofuels could easily go the same way, if only governments are forward-thinking enough to see the potential and invest.

Spinning Straw into Gold

By Sophie Harrington

Everyday millions of people around the country hop into their cars and drive off to work, school, or the shops. This has become such a routine part of our lifestyle that few of us stop to think about what we’re using to power those trips, except when the prices hike or, as we’ve seen recently, drop. Most of us realise that, despite the trumpeted new sources of oil in the Arctic, our petrol habit is highly unsustainable. Wouldn’t it be nice if we could keep our cars and buses running, but on a renewable form of energy?

Some of this has already come to fruition, with cars in the US being driven on up to 15% ethanol derived from corn stalks. This is even more successful in Brazil, where thanks to cars with “flexifuel” engines, drivers are able to fill up with either pure ethanol, or an ethanol/petrol blend depending on the price on a specific day. What a success!

Sugar cane waste, known as bagasse, could one day be used to fuel our cars. (Credit Tele Jane @Flickr)

Sugar cane waste, known as bagasse, could one day be used to fuel our cars. (Credit Tele Jane @Flickr)

Yet this too comes with downside, most notably the appropriation of food (often in the form of maize) for biofuels. While this might not be so obvious to those living in the Western world, sheltered from changing food prices thanks to a wall of subsidies and favourable trade policies, the increasing demand for biofuels has succeeded in driving up the price of such staple grain, seriously hurting net-importing countries. In 2008, riots broke out across the world, from Mexico and Morocco in part due to a sudden, sharp rise in grain prices, partially due to increased demand for biofuel materials in the US and other more developed nations.

Here we are at an impasse—how to both wean ourselves off of unsustainable fossil fuels while ensuring that such biofuel production does not impinge on food production? The answer may lie in technologies still in the development stage, where biofuel is instead derived from agricultural waste and marginal lands. These lignocellulosic biofuels aim to extract sugars from the tough, indigestible material left behind after harvest or extraction of traditional ethanol. By breeding varieties with more easily digestible cell walls, it’s hoped that the extraction of sugar from this material will become not only easier by financially feasible.

Plant cell walls are made up of a host of different components, whose interactions serve to increase the recalcitrance, or toughness, of the wall. This makes it hard for enzymes to digest, which is a benefit when protecting from pests and diseases but hinders exploitation of the sugars. Recent research has focused on modifying the structure and components of the cell wall, thus allowing enzymes better access to break it down. Such research has shown recent success, with variations in hemicellulose structure (a key component linking cellulose fibers in the wall) resulting in increased digestibility and sugar release.

Considering the vast amounts of agricultural waste that are currently either left to rot, or burnt for electricity, a process that could convert this into useful biofuel and other high-value products has the potential to significantly contribute to the fuel consumption. It might seem a bit like Rumplestiltskin asking for straw to be spun into gold, but lignocellulosic biofuels are rapidly becoming more feasible. Here’s hoping that funding bodies and industry giants continue to invest in this exciting alternative to fossil fuels.

Hook, Line, and Sinker: Rise of the Killer Mushrooms

By Nathan Smith

Pleurotus ostreatus, or the oyster mushroom, is a common edible mushroom. As much at home in a stir fry or a soup, one would not expect this culinary baseline to be anywhere other than at the bottom of the food chain. Surprisingly this is not the case, as the oyster mushroom is a stealthy and efficient predator of nematodes.

Pleurotus ostreatus-- a killer in disguise?

Pleurotus ostreatus— a killer in disguise? (Credit Jean-Pol GRANDMONT)

Nematodes, a type of worm, are infamous agricultural pests. The damage caused by these miniature beasts has been estimated at $US80 billion per year, though this is believed to be a severe underestimate as many growers are unaware of them. They even present a threat to the cultivated mushroom industry, being a renowned pest of button mushrooms, so how is it that they fall prey to the oyster mushroom?

The answer is one of ingenuity on the part of the fungus. Unable to chase the nematodes, mushrooms are notoriously sessile, it instead lays a trap. It secretes a toxin which, upon contact with a nematode, proceeds to immobilise the worm in as little as 30 seconds. Fungal hyphae, attracted to the (still alive) nematode through host leakage products released by immobilisation, penetrate one or more of the nematode’s orifices and proceed to digest it.

The unrelated fungus Arthrobotrys also hunts nematodes, but through a completely different mechanism. Instead of stunning its host, it captures it in a hyphal lasso. Known as a constriction ring, this consists of a hypha fused with itself to form a three-celled ring about 20-30 microns in diameter. If, and when, a nematode enters the ring, it triggers the three cells to expand rapidly (within 1/10th of a second) and trap the nematode.

Killer fungi aren’t just of academic interest either. The hunting abilities of fungi, particularly the oyster mushroom, make them potential effective and green bio-control agents. Indeed, initial tests have found the oyster mushroom effective at controlling the Sugar Beet Nematode (Heterodera schachtii), through field tests have yet to be carried out.

It appears that fungi aren’t just passive members of the woodland scenery but rather edible guardians protecting against the nematode threat.

Who said organic farming was less productive?

By Stephan Kamrad

A while ago Joanna reported on a chemical free, organic pest control method that has a lot of advantages to conventionally used pesticides. Studies have shown that organic and comparable agriculture is more sustainable, as measured by indicators like species richness, soil fertility and nitrogen uptake. But even by most experts it is usually dismissed as a fantastical ideal that conflicts fundamentally with our need to feed the growing human population. This month, a new meta-study, published in the Proceedings of the Royal Society B, by scientists from the University of California reveals that the productivity gap between organic and conventional farming might be much smaller than widely believed.

Not so great after all? Credit www.CGPGrey.com

Not so great after all? Credit www.CGPGrey.com

The researchers analysed 115 studies covering over 30 countries and 50 crop species. Organic farming, defined by having no synthetic inputs, was found to be on average 19% (±4%) less productive than conventional farming. But interestingly, this obviously quite a drastic gap shrinks down to 9% (±4%) when the organic farmers use a polycrop system compared to a conventional monoculture. In polycrops, multiple species are grown together, e.g. in alternating rows, resulting in a greater biodiversity than conventional monocultures. This makes them less susceptible to disease and pests and certain combination of crops can act as biological pest repellants and natural fertilisers. In Joanna’s example in Kenya, maize was planted together with Desmodium (which repels the vicious Stemborer moth and also fixes atmospheric nitrogen). Another popular example found in British gardens is intercropping of tomatoes, onions and marigold.

The yield gap was also much smaller (8±5%) when organic farmers used crop rotations, i.e. planted a different crop in each growing season, a system which was once (in the Middle Ages) quite popular in Europe.

But where is the catch? If these techniques are so effective, why are they not used everywhere? More diverse systems are much more difficult to manage. Massive machinery cannot easily be used with companion crops and it is often advantageous for farmers to sell only one or a few crops in bulk. For small farmers in developing countries these techniques are easier to adapt but farmers often are not aware of the possibilities.

All this of course might be slightly too optimistic. After all, non-organic agriculture can also make use of intercropping (rare) or crop rotations (more common). In studies where conventional farming (i.e. the use of pesticides, weed-killers and synthetic fertilisers) was combined with polycropping or crop rotation, the yield gap returned to its original value or was even higher.

Interestingly, the yield gap also depends on what type of crop is under consideration. The yield ratio of organic to conventional farming is lowest for cereal crops, where a lot of effort has gone into the development of high intensity, large scale monocultures but often comes close to 1 for fruits and nuts, were less effort has been made in developing high output systems.

In our world, it is very hard to convince a farmer that he should tolerate a 9% or even 20% yield decrease for the prospect of a healthier agro-ecosystem, that is diverse, unpolluted and resilient to stress and disease. Diversification (be it over time as in crop rotations or over space as in polycrops) can raise organic farming yields and make it more competitive to conventional farming. With more investment it may be possible for the yield gap to be reduced even further.

Reference:

Ponisio LC, M’Gonigle LK, Mace KC, Palomino J, de Valpine P, Kremen C. (2015) Diversification practices reduce organic to conventional yield gap. Proc. R. Soc. B, 282:20141396. DIO: dx.doi.org/10.1098/rspb.2014.1396