By Britt Lewis Recent concerns about phosphorous sustainability are fueled by the persistent overuse of phosphorous in fertilizers to increase crop yields. On the one hand, the United States has increased food production to both feed a growing population and produce biofuels. On the other hand, using phosphorus-laden fertilizers has imbalanced crop cycles and polluted surface water, even killing off an area the size of New Jersey in the Gulf of Mexico.
Phosphorus mine reserves are quickly diminishing, which has led to scarcity predictions worldwide. With phosphorus as vital to agriculture as water, food security hangs in the balance.
The following is a Q&A conversation with Dr. Roberto Gaxiola, an assistant professor at Arizona State University, whose research explores the role that transgenic crops might play in sustaining agriculture under limited phosphorus conditions.
(Editor’s Note: The terms "phosphorus" and "phosphate" are used throughout the article. Phosphate is a compound containing phosphorus, and plants can use phosphate as a nutrient.)
Recent efforts in the science community have been focused on bringing attention to the issue of phosphorus sustainability, which has been called "the biggest problem you never heard of." Why is this a major problem and why has it largely been ignored?
I would be imprecise if I tried to cover all of the different areas that make P [phosphorus] sustainability a major problem, so let's focus on the area my group is working with, namely agriculture. After the green revolution, we developed plants that were selected to produce higher yields at the expense of excess use of fertilizers and water. These plants generated a big boom of production. It's also relevant to say that only people and countries that had the economic capacity to buy the fertilizers benefitted. The enhanced food production was impressive, but now we are paying the consequences of that boom as the plants that we selected for this kind of response are plants that, in a sense, "got lazy" and did not develop root systems capable of scavenging nutrients and water from the soil. In other words, we are bringing them a lot of food, so they don't need to go and get their food. That resulted in plants that have a reduced nutrient uptake capacity – phosphate and nitrate uptake capacity. Farmers know that insufficient P fertilizer reduces crop yields, so they continually add P to their fields. Global consumption of P is increasing about 3 percent annually, and about 60 percent of the world’s P comes from one country (Morocco). Concerns have begun to arise about the long-term prospects of the global P supply and its geopolitical implications.
Another problem is the pollution that excessive P fertilization generates. The P that plants do not use is either fixed by the soil or washed into the water bodies generating a problem called eutrophication. Eutrophication results from an excess of P in the diet of algae that enhances their growth in water, which could be seawater or freshwater. The algae eventually will die and sink to the bottom, and the bacteria that decompose them consume a lot of oxygen generating huge areas that lack oxygen and cause mortality of the other members of the ecosystem.
Are you referring to coastal dead zones?
Yes, exactly – like the dead zones in the Gulf of Mexico.
When did you first become aware of concerns in the science community about phosphorus scarcity?
My initial interest in agriculture was salinity of the soils – especially the soils in arid and semi-arid regions of the planet – which are the most productive areas of the world due to longer days and higher temperatures ideal for photosynthesis. Those areas were used by the green revolution, and those areas were receiving a lot of fertilizers and water. Fertilizers are presented as different kinds of salts, and one of the results of this massive fertilization was the accumulation of salts on the top soil. Well those salts, mainly NaCl (sodium chloride or table salt), are toxic for plants. The crops we actually consume, like corn, cannot tolerate above 50 mM of sodium chloride. (For example, the ocean contains 400 mM of salt. A corn plant will die with 50 mM; they are very sensitive.) My initial idea was to learn how plants adapt to this salty environment because in nature we have plants that actually grow in the presence of high salt (more than 1000 mM), like mangroves. So I started studying that and looked at the players involved in sodium detoxification. By doing so, we identified some key plant genes, and then we were able to generate transgenic plants that were salt tolerant. Interestingly, these salt tolerant plants were also very large plants with enormous root systems, and their characterization has revealed that they have an enhanced nutrient (phosphate, nitrate and potassium) uptake capacity.
That's a good thing, right?
Yes. One important thing that we have to emphasize is that plants in nature don't grow to produce food for us – their only goal is to reproduce. So the plants that we have domesticated have been altered, so now they produce more food for us, but that's not the normal goal of a plant. So when people talk about eating natural plants, they are imprecise. Nobody really eats any natural plants. Mostly, we have domesticated the plants that we consume. We have used different means for domestication. Now, we are using more sophisticated technology, like genetic engineering. We have tweaked them in many different ways, and now we have precision tools to actually go and manipulate one specific unit of genetic information (gene) and get a result. So when we saw these plants that have enhanced root systems, the first question was: How do they behave under limited phosphorus conditions? Well, these genetically modified salt tolerant plants are very efficient [at] taking up phosphate, especially in alkaline soils (like those of Africa). These plants develop root systems with very long root hairs, specialized in taking up nutrients, and they use those modified root systems to scavenge phosphorus via acidification.
Does this work in other kinds of plants?
It works in other plants too. It is a very natural phenomenon; I emphasize this because genetic engineering has been demonized.
Yes, and that touches on a question I had about genetic engineering: What is the origin of this negative stigma surrounding genetic engineering that is reflected in rhetoric of popular culture?
I do not know. In general, history shows that people are resistant to changes. We have a potential geopolitical problem regarding P availability. The situation is that we have one country in possession of about 60 percent of the phosphorus of the world, and that country is Morocco. And we have countries like India where there is no availability of so-called "cheap" phosphorus for fertilizers. The United States has phosphorus mines for relatively cheap phosphorus, but the extraction of phosphorus is getting more and more expensive because the easy phosphorus has been taken. So now they have to go and get deeper phosphorus, which is more expensive. This shift already has been reflected a little bit in price of phosphorus. So another strategy will need to address optimizing extraction processes. How we address phosphorus sustainability will have to be a multidisciplinary and concerted effort, and one aspect is making these processes to extract phosphorus more profitable and more efficient. That will be a technical challenge for engineers.
From the agriculture side, we need to make crops more efficient. One important thing to emphasize is the fact that there is a lot of phosphorus bound to the soil that crops normally can't acquire because they lost their capacity to scavenge, or their capacity is toned down. So GMO plants with an enhanced P scavenging capacity, with other approaches, can help to optimize P sustainability.
I think that genetic engineering is going to play an important role – not the only one – but in order to overcome public concerns, a well-designed information campaign is necessary.
What about the organic food movement – will it play a role?
The organic story is about reducing the use of pesticides. It's a very nice and romantic story, but it's not a practical one. Organic agriculture will not be able to generate food to feed the huge cities we have generated. Civilization has developed as it has – whether it is right or wrong is another question. You cannot feed a city like Phoenix with organics. It's impossible. I don't see another option; organics, at least, do not provide that option. If you are rich enough to pay the prices for organics, then that's okay. But I'm more concerned about the people who cannot eat. A lot of the unrest that we are seeing in the Middle East is coming from food security. People can be abused – and they have been abused for a while – but their food supply was still sufficient. Scarcity is starting to hit. When food scarcity hits, it's a major problem.
In the timeline of genetically modified plants, where are we now?
We are ready, and China is taking the lead. China is already growing genetically modified plants that already have been approved by the Chinese department of agriculture. Here in the United States, you can grow genetically modified plants after passing all the challenges. If the challenges weren't so dramatically high, ASU could promote the growth of the plants I'm generating – but the price is so high that only a big company can do it. So one of the main dangers is that we might have in the near future a monopoly of agricultural goods. I think that is dangerous for the whole world.
In 20 years from now, what is your hope for Earth in relation to phosphorus scarcity?
I think we will be in a good place. There is enough technology at different fronts that will actually help to address the problem. Morocco remains ... a question mark, but again, the research and the technologies hold a lot of promise. It's just a matter of using them.
Britt Lewis is a graduate student in the Department of English at Arizona State University, where she is studying ecocriticism.