Category Archives: Life

AoB Interviews: Hans Lambers on soil phosphate acquisition in impoverished soil

This week guest author Charlie Haynes is AoB Blog’s roving reporter at the EPSO/FESPB plant biology Europe conference.

 

Hans Lambers Hans Lambers is the Winthrop Professor at the University of Western Australia. He competed his PhD in 1979 at the University of Groningen in the Netherlands and since then worked at Melbourne University, Australian National University and Utrecht University. His research focuses on mineral nutrition of native Australian plants and crop and pasture legumes. He very kindly agreed to talk to me about some of the challenges of soil phosphate impoverishment.

Why is phosphate impoverishment so significant?
It’s of less importance in Europe which imports food and animal feed from parts of the world where phosphates passing the problem on. There it is an issue of excess of phosphate, dumped on the land and ending up in waterways. Europe could stop fertilising now and still have crops for the next 20 years. But when you go to other parts of the world; Australia, South America, Africa and South East Asia, phosphate insecurity is a real issue. This may be because the amount in the soil is too low for effective crop production, or it may be that it is there but it’s not readily available. So it’s an issue for crop production and thus food security. What we can do though is instead grow plants that can use that phosphorus in the soil much more effectively. There is a tremendous opportunity.

How does this limit these countries in what they can grow and the yields they can produce?
In Africa phosphorus is the key limiting factor, even some the driest areas of Saharan Africa. People who worked in barchenener discovered that simply by adding phosphorus you could get a higher yield. The dry soil significantly reduces the mobility of phosphorus in the soil and it becomes a significant limiting when you have a dry soil (Lambers H, Raven JA, Shaver GR, Smith SE. (2008) Plant nutrient-acquisition strategies change with soil age. Trends in Ecology and Evolution 23: 95-103).

So why do these communities not buy fertiliser to increase their yield?
Fertiliser is very expensive for these groups. It has to travel vast distances to the harvest, and these groups simply don’t have the money for it. So there instead we are working towards crops that are more efficient at using the existing phosphorus or are better at getting it out of the soil. This is however a bit of a risky business – if you have soils that are very nutrient poor to begin with then plants that extract it more effectively will make the soil even more phosphorus deficient. Whatever you take out of soil have to replace in order to be sustainable.

What makes phosphates accessible?
Phosphates in soil are readily available at a neutral pH. Calcareous soils with their more alkali pH lock phosphates up in calcium complexes. The phosphate is there but not readily available to crops. More acidic soils also lock up phosphates – but this time not in calcium complexes but instead, as complexes of oxides and hydroxides of iron and aluminium. Chile has very acidic soil, with a pH of almost 4, and lots of these metal oxides and hydroxides so all the phosphate isn’t readily available. However the plants have special adaptations that allow them to access it in these conditions.

What are these adaptions?
These plants have a special structure which works in combination with the plant biochemistry. What they produce is massive quantities of carboxylates. These are molecules with a negative charge – like phosphate. These exchange for one another, releasing the phosphate ions into the soil solution, whilst carboxylates anion take the place of phosphate in the soil. You’re effectively mining the phosphate that is in the soil out of it’s tight bindings. It’s then in the solution and anybody can take it up (Lambers H, Bishop JG, Hopper SD, Laliberté E, Zúñiga-Feest A. (2012) Phosphorus-mobilization ecosystem engineering: the roles of cluster roots and carboxylate exudation in young P-limited ecosystems. Annals of Botany 110: 329-348).

Could this be put into another crop either by breeding or genetic modification?
I would take one step back and ask ‘what crops do we have now at already can do that’? White Lupin is an excellent example and there are a few other Lupin species that do exactly the same. There are also some Lupin species that don’t have these wonderful structures but instead something close to it, and some without a structure at all that still release carboxylates. So we actually already have a lot of species that can already played this trick. Rather than engineer this in Soybean, it’s important to get a thorough understanding of the technology. Understanding is and farming it in crops with the gene is an obvious first stage. We already have crops with the this ability in lupins – which are much better than wheat and barley at this stage. I don’t think it’s impossible but it’s important to take it one step at a time (Lambers H, Clements JC, Nelson MN. (2013) How a phosphorus-acquisition strategy based on carboxylate exudation powers the success and agronomic potential of lupines (Lupinus, Fabaceae). American Journal of Botany 100: 263-288).

So are some parts of the world focusing on the wrong crops for their soil type and climate?
Yes absolutely! In chile they used to grow Andean Lupin. When the Spanish invaded they forbade the natives from growing these lupins as they weren’t Spanish crops. The natives switching to foreign crops is a daft idea when they already had a crop suited to their environment! Quinoa is an example of another crop where this happened, and the Spanish stopped that. They arguably had better crops than the foreign spanish ones then introduced. One thing one can do though is intercropping. This is where you grow plants concurrently interspersed between one another. If you want to grow wheat, it cannot grow particularly well in some South American environments. If you intercrop it with Lupin, can mobilise that phosphorus and the neighbours can benefit from that. You can also do crop rotation. A group in Germany has actually done this, working with rotations of soybean and maize. Maize is not so good at accessing phosphate, soybean – depending on the cultivar you use, is. The good soybean cultivars show a real benefit for the next crop – a phosphorus benefit. You can grow them at the same time or you can grow them in rotation to access this phosphate. Both of these techniques have tremendous benefits.

What stops people in phosphorus poor environments from doing this already?
That’s an interesting question. If you go to china, intercropping has been done for hundreds of years and you can demonstrate that with the right intercropping combinations you can have a 40-50% higher yield – which is pretty impressive! A British or Irish farmer with an increase in yield of that kind of level would be ecstatic! So the Chinese already have done that, and Europe is exploring it. I’m certain it could be done in other parts of the world, but it’s not happening on a large scale and that’s because a lack of education. It’s important to educate local farmers about this from Africa to Australia! I’m working with a group in Germany Andreas Burgutts, who is screening sorghums for better phosphate accessibility, using leaf manganese levels as a marker. These are taken up by the plant in the same as as phosphates and so used as a marker. Work like this requires going to Africa, and selecting the right cultivar for the conditions there, not in our lab field. This is about doing research and then making use this research reaches farmers, and doesn’t stay in a scientist’s ivory tower. Work needs to be done and go beyond journals, into places where we can make a difference,

Who else is working on taking this knowledge into the field?
I had a visit from someone from ICRISAT. They are based in India and work on major crop draught and salinity. They are now keen to work on phosphorus, and they had heard of my work and were interested in developing something together. These big international institutes have the links with the grassroots farming communities in the parts of the world where you can truly make a difference. I may be able to do high end science but without the connections I’m not able to have much of a real world impact.

Who else is involved?
The big international institutes are doing good work, IRRI in the Philippines, ICARDA in Aleppo and ICRISAT in Hyderabad. These large international institutes aren’t just interested in the science, but also applying it, and I think that is really important.

Do these plants have potential in any other key areas?
Yes, for instance where you have soil contaminated with heavy metals you could use them in the process of photoremediation. Here plants as used for their ability to remove heavy metals an ‘clean’ soil. There are areas in Belgium that have been heavily polluted with zinc or copper. Chemical or physical cleaning of this soil is almost impossible. You need a species that accumulates these metals to a very high concentration, but is also a fast grower, producing a lot of biomass, or else the process takes along time. There is serious potential in this. In addition to this these plants can be used in phytomining or prospecting, accumulating small amounts of metals that act as an indicator for a larger deposit of metal in the earth. This can act as a pretty good indicator of gold and some other metals to allow groups to commence mining.
Hans’ book “Plant Life on the Sandplains in Southwest Australia, a Global Biodiversity Hotspot” will be out in September, and is now available online at the UWA Publishing website.

 

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Plantspersons in the public eye…

Image: Wikimedia Commons.

Image: Wikimedia Commons.

The razzle-dazzle of the luvvie-filled media circi that celebrate the celebrities of the entertainment world, such as the UK’s Baftas and the USA-dominated Oscars, make it easy to get suckered into that evanescent world and forget what truly endures and matters more. So, let’s pause for a moment and reflect on those individuals whose achievements usually go unsung, the celebrities of the plant world. No, not the plants themselves – though they are always deserving of centre-stageness and our attention, awe and admiration – but the people that have done noteworthy things. Whilst they might not always win prizes – though some of them have (but it’s not really about prizes anyway…) – their various stories do show that those who work with plants can get credit for a job well done, and one which is usually going to continue to have impact long after the event. So, this and my next post are on that theme.

 

[So, who did win the Oscar for best representation of a botanist – living, dead or fictional – in a film? – Ed.]

 

On top down-under…

Image: USDA ARS/Wikimedia Commons.

Image: USDA ARS/Wikimedia Commons.

First up is Australian National University Distinguished Professor Graham Farquhar AO, FAA, FRS, NAS and CSIRO Fellow Dr Richard Richards FAA who were awarded the 2014 Rank Prize in Human and Animal Nutrition and Crop HusbandryThe Rank Prize Funds is a charitable organisation that seeks to recognise excellence in specific fields of research and reward innovators for their dedication and outstanding contribution. They received £40,000 (each) for pioneering the understanding of isotope discrimination in plants and its application to breed wheat varieties that use water more efficiently. Although the award relates to their discovery in the 1980s, when they found a way to predict the amount of water needed to best grow different types of wheat, given the increasing concerns over future food/energy/water security,  and efficient use of water by plants,  the work is likely to have major relevance to feeding the planet in the short and medium term. And this award also goes to show that the seeds of future success may take many years to grow and blossom into recognition.

 

[Oh, almost forgot! Prof. Farquhar also shared in the 2007 Nobel Peace Prize as part of the Intergovernmental Panel on Climate Change,  and in 1995 was elected a Fellow of the UK’s Royal Society…!!! – Ed.]

 

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Seeking Part-time Social Media Editor for AoB PLANTS

AoB PLANTS, the premier open-access journal for plant sciences, is seeking a part-time social media editor to develop features for our website and to expand the journal’s presence on Facebook, Twitter, blogs and other social media outlets, with the general objective of increasing the visibility, influence and reputation of our journal.

 

The ideal candidate will meet the following criteria:

• a graduate degree in biology

• demonstrated research experience in some area of the plant sciences

• in-depth knowledge of social-media tools and applications

• evidence of social-media publishing experience

 

For details see http://bit.ly/1wfniSJ. Interested individuals should contact the Chief Editor Hall Cushman (cushman@aobplants.org) and/or Managing Editor Gail Rice (rice@aobplants.org).

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Spotlight on macronutrients (Part 2): Nitrogen, in a bit of a fix…

Image: Wikimedia Commons.

Image: Wikimedia Commons.

In this and my next few posts we conclude our look at essential plant macronutrients that started in some previous articles, and this time concentrate on the last four of the nine elements – C, H, O, P, K, N, S, Ca and Mg – in that category (and try to bring a Cuttings-esque twist to that quartet).

 

Nitrogen, in a bit of a fix…

Nitrogen (N) is a major component of many compounds in plants, e.g. it is present in all amino acids, which are the building blocks of proteins – and hence cell membranesenzymes and nutritionally important storage or reserve proteins; and it is an important constituent of nucleotides, which are major components of nucleic acids, such as RNA (ribonucleic acid) and DNA (deoxyribonucleic acid), and of the ‘energy molecule’ ATP (adenosine triphosphate). As a major component of plants, N is needed in relatively large amounts – which is why it is termed a macronutrient. Fortunate then, you might think, that plants are virtually surrounded by an unlimited amount of nitrogen in the atmosphere,  which consists of approx. 78% of this gaseous element in the form of dinitrogen, N2. Sadly, in that state plants cannot use it; it must be converted to forms that they can use, such as the ammonium (NH4+, from ammonia – NH3) and nitrate (NO3) ions.

 

Whilst plants cannot themselves convert N2 into NH3, many groups of plants – e.g. famously, the legumes – have teamed up with bacteria that can undertake that chemical reaction in the process known as nitrogen fixation. Some of that fixed nitrogen is used by the plant that hosts the mutualistic microbe, as a sort of rent for the home that the plant provides for the bacteria within root-sited nodules.

 

Unfortunately, many more plants are not blessed with this in-built nitrogen-fixing partnership and are reliant on appropriate forms of fixed nitrogen from the environment, e.g. NO3. Since N is frequently in short supply in the soil, it is often referred to as a limiting nutrient – an essential nutrient whose amount limits overall plant growth and development. In agricultural settings this deficiency is usually remedied by the addition of chemical fertilisers, often containing phosphorus (P) and potassium (K) in addition to the N. Whilst desired increases in crop growth/yield are obtained by this human intervention, not all of that added nitrogen – and frequently phosphorus, too – is taken up by the crop; substantial amounts of N and P end up in freshwater systems where they can cause highly undesirable problems such as eutrophication. Not only is that damaging to the environment, it is costly – ‘Nitrogen fertilizer costs US farmers approximately US$8 billion each year…’.

Wouldn’t it be great if non-legumes could be persuaded to develop N-fixing bacterial partnerships? Yes, and work by Yan Liang et al. (Science 341: 1384–1387, 2013) encourages that view. The team from The Plant Molecular Biology and Biotechnology Research Center (South Korea) and University of Missouri (USA) have demonstrated that non-legumes – in this instance good old Arabidopsis thaliana, Zea mays (‘corn’) and Solanum lycopersicum (tomato) – do have the ability to respond to the rhizobial lipo-chitin Nod factors that are released by the would-be symbiotic rhizobial bacteria, and which are signal molecules that trigger nodulation in legumes. Although we are still some time away from nodulating N-fixing non-legume crops such as maize and tomato, this discovery does at least show that the rhizobia are recognized as ‘friendly bacteria’ – the plants just have to be trained to let them accept invasion of their tissues by the microbe, and build the nodule, etc, etc…

 

[Although there are generally recognised to be 17 essential plant nutrientscobalt (Co) is additionally required by the bacteria of the N-fixing nodules,  so indirectly Co is an 18th essential nutrient in those cases – Ed.]

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The May 2013 issue of Annals of Botany is now free access

A flower of Paederia

A flower of Paederia, a pantropical genus of woody lianas, together with a map of its inferred dispersal from an origin in the Oligocene in tropical continental Asia. Long-distance dispersal such as this may be much more common than previously thought and may represent an important mechanism in the assembly of modern tropical floras. See Nie et al.

The May 2013 issue of Annals of Botany is now free access. The cover image for this month is a flower that looks quite different, depending on where in the tropics you look at it. Why isn’t there a smooth variation in form as you travel round the world? Nie et al propose that the answer is because Paederia didn’t spread slowly overland.

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Blogging can have a negative effect

The cat is surprised

Shocking news on blogging. Photo Michelle Tribe / Flickr.

At AoB Blog we encourage scientists to blog because we think it’s a good idea for scientists to tell people about their research, including other scientists. Some measures like Altmetric and Impact Story think this is a good thing too, but not everyone does.

Yesterday PeerJ posted a presentation on their blog, where Jonathan Eisen shows how some grant reviewers can hold blogging against you.

Let’s hope this doesn’t dissuade new journal Nature Plants from posting to their new blog.

hat-tip to Anne Osterrieder.

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Clean drinking water via plants

Xylem structure Effective devices for providing safe drinking water are urgently needed to reduce the global burden of waterborne disease. A recent paper in PLoS ONE shows that plant xylem from the sapwood of coniferous trees – a readily available, inexpensive, biodegradable, and disposable material – can remove bacteria from water by simple pressure-driven filtration. Approximately 3 cm3 of sapwood can filter water at the rate of several liters per day, sufficient to meet the clean drinking water needs of one person. The results demonstrate the potential of plant xylem to address the need for pathogen-free drinking water in developing countries and resource-limited settings.

Since angiosperms (flowering plants, including hardwood trees) have larger xylem vessels that are more effective at conducting sap, xylem tissue constitutes a smaller fraction of the cross-section area of their trunks or branches, which is not ideal in the context of filtration. The long length of their xylem vessels also implies that a large thickness (centimeters to meters) of xylem tissue will be required to achieve any filtration effect at all – filters that are thinner than the average vessel length will just allow water to flow through the vessels without filtering it through pit membranes. In contrast, gymnosperms (conifers, including softwood trees) have short tracheids that would force water to flow through pit membranes even for small thicknesses (<1 cm) of xylem tissue. Since tracheids have smaller diameters and are shorter, they offer higher resistance to flow, but typically a greater fraction of the stem cross-section area is devoted to conducting xylem tissue. For example, in the pine branch used in this study, fluid-conducting xylem constitutes the majority of the cross-section. This reasoning leads the authors to the conclusion that in general the xylem tissue of coniferous trees – i.e. the sapwood – is likely to be the most suitable xylem tissue for construction of a water filtration device, at least for filtration of bacteria, protozoa, and other pathogens on the micron or larger scale.

Boutilier MSH, Lee J, Chambers V, Venkatesh V, Karnik R (2014) Water Filtration Using Plant Xylem. PLoS ONE 9(2): e89934. doi:10.1371/journal.pone.0089934

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It’s our secret, the Science of Rumour

Humans are social creatures and we love to share gossip, but we share what we like, not necessarily what is true. So are you living in a golden age of misinformation? If you are how would you know? This week Aleks Krotoski discusses Whispers on The Digital Human, a series that explores how connections via modern media are changing human behaviour.

Aleks Krotowski. Photo: BBC.

Aleks Krotowski. Photo: BBC.

It’s relevant to scientists because spreading information is what most scientists hope they do. Yet it seems that social networks are fertile ground for spreading misinformation. Why is that?

One answer suggested in the programme is that it’s down to how the scoring system works on social media. There are no obvious points to be won on Facebook or Twitter, but if you look below you’ll see sharing buttons. They’ll have numbers by them and even though they’re not really a score bigger numbers are better.

There’s also evidence that we choose our own realities, which may or may not coincide with the reality happening outside our skulls.

This is going to be a problem if your research finds a reality that people don’t like, whether that’s Anthropogenic Global Warming is real, or that GMOs are not inherently more of a safety hazard than other plants.

Another problem is that evidence proving a rumour false, might increase belief in the rumour. On the one hand this might be simple conspiracy theory – they wouldn’t try disproving it unless it was true. However, there’s also evidence that the way memory works reinforces rumour when you disprove it.

It’s easy to listen to the programme and look at the issues as something that affects other people. Did people really believe a tiger was roaming the streets of London in 2011? But the counterpoint is, what do you believe that is rumour, and do you really have time to fact check everything?

You can stream the programme on Radio 4, it’s available worldwide, or download a 13 megabyte MP3 file.

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Revving up photosynthesis with nanotechnology – take that, greenhouse effect!

Carbon nanotube What happens when you insert single-walled carbon nanotubes into the leaves of Arabidopsis? The semiconducting nanotubes integrate themselves into the chloroplasts’ outer envelope and triple photosynthetic activity by enhancing electron transport.

So should we be making genetically modified plants containing carbon nanotubes? Well probably not – you have to believe that 3.5 billion years of evolution has optimised photosynthesis pretty well to achieve a nice balance. But that doen’t mean that this research is without applications, such as making living leaves that perform non-biological functions (for example, detecting pollutants or pesticides), or constructing artificial energy harvesting systems which don’t contribute to climate change.

Plant nanobionics approach to augment photosynthesis and biochemical sensing. (2014) Nature Materials 13, 400–408 doi:10.1038/nmat3890 [Subscription]
Abstract: The interface between plant organelles and non-biological nanostructures has the potential to impart organelles with new and enhanced functions. Here, we show that single-walled carbon nanotubes (SWNTs) passively transport and irreversibly localize within the lipid envelope of extracted plant chloroplasts, promote over three times higher photosynthetic activity than that of controls, and enhance maximum electron transport rates. The SWNT–chloroplast assemblies also enable higher rates of leaf electron transport in vivo through a mechanism consistent with augmented photoabsorption. Concentrations of reactive oxygen species inside extracted chloroplasts are significantly suppressed by delivering poly(acrylic acid)–nanoceria or SWNT–nanoceria complexes. Moreover, we show that SWNTs enable near-infrared fluorescence monitoring of nitric oxide both ex vivo and in vivo, thus demonstrating that a plant can be augmented to function as a photonic chemical sensor. Nanobionics engineering of plant function may contribute to the development of biomimetic materials for light-harvesting and biochemical detection with regenerative properties and enhanced efficiency.

Bioinspired materials: Boosting plant biology. Nature Materials News & Views (2014) 13, 329–331 doi:10.1038/nmat3926 [Subscription]

 

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