In the coming decades, humanity will have to feed billions more people on a planet under pressure. extreme heat waves, intense droughts, and degraded soilsGiven this scenario, the way we cultivate and understand plants is changing rapidly, and one of the most fascinating lines of research is that of what are colloquially called "nitrogen-breathing plants".
Behind this striking idea lies a gigantic challenge: getting crops to be able to harness nitrogen from the air and reduce dependence on chemical fertilizersWhile adapting to a warmer, drier, and more variable climate, leading centers like the Centre for Plant Biotechnology and Genomics (CBGP) are already fully engaged in this challenge, combining biotechnology, ecology, and sustainable agriculture to sustain food production in a constantly changing world.
Why is nitrogen so important for plants?
It may sound exaggerated, but without nitrogen there would be no life as we know it, because this element is key for plants to form proteins, enzymes and pigments necessary for photosynthesisWithout an adequate source of nitrogen, a crop cannot grow well, produce biomass, or offer acceptable yields.
Although the air we breathe is made up of around a 78% nitrogen gas (N₂)Plants cannot use it directly. Atmospheric nitrogen is very stable, and most living things lack the biochemical tools to break down this molecule and transform it into usable compounds like ammonium or nitrate.
Under natural conditions, plants obtain nitrogen mainly from the soil, in the form of nitrate (NO₃⁻) and ammonium (NH₄⁺) ionsThese nutrients come from the decomposition of organic matter or from biological fixation processes carried out by microorganisms. When the soil is poor in nitrogen, plants suffer from chlorosis, grow poorly, and their productivity plummets.
To compensate for this limitation, modern agriculture has relied on synthetic fertilizers that supply large quantities of nitrogen. The problem is that the model has become unsustainable due to high energy consumption, carbon footprint, and pollution of soil, water and atmosphere associated with the overuse of chemical fertilizers.
Much of the current research focuses on understanding and better harnessing the natural strategies by which some organisms and some plant-microbe associations are able to to fix atmospheric nitrogen and make it available to ecosystems.
Biological nitrogen fixation: the trick of bacteria
While plants cannot use nitrogen gas directly, certain bacteria can, thanks to a a highly specialized enzyme called nitrogenaseThis protein is able to break down atmospheric N₂ and transform it into nitrogenous compounds that, over time, become part of the food chain.
These nitrogen-fixing bacteria are found both freely in the soil and in close association with the roots of certain plant species. Some of them establish very close symbiotic relationships with plants, living inside special structures that form in the roots and allow a very finely tuned exchange of resources.
In so-called symbiotic nitrogen-fixing plants, the plant hosts the bacteria and supplies it with sugars obtained through photosynthesis, while the microorganism returns the favor. providing “new” nitrogen from the atmosphereThis exchange is so efficient that it can cover a large part of the crop's needs and enrich the soil for future plants.
When these plants associated with bacteria complete their life cycle and their remains are incorporated into the soil, the nitrogen they had accumulated in their tissues is released through a process known as nitrogen mineralizationOrganic matter decomposes and organic nitrogen is transformed into ammonium and nitrate, forms that other plants can easily absorb.
Thus, plant communities that include nitrogen fixers play a crucial role in the natural fertility of many ecosystems and agricultural systemsreducing the need to supply so much external fertilizer.
Plants that “breathe” nitrogen: legumes, nodules and symbiosis
The best-known group of plants associated with nitrogen-fixing bacteria is the legumes, a huge family that includes everyday crops such as peas, beans, lentils, chickpeas, broad beans or cloverThese species have developed, throughout evolution, the ability to form nodules on their roots to provide shelter for specific bacteria.
In this relationship, the plant emits chemical signals into the root zone that attract certain soil bacteria capable of fixing nitrogen. Once contact is established, the root begins to form specialized structures called noduleswhich act as small, protected “biological reactors”, where bacteria live and work under suitable conditions.
Within these nodules, bacteria fix atmospheric nitrogen and transform it into nitrogenous compounds that flow into the plant, while the plant sends sugars and other compounds to the bacteria to keep them active. Although these microorganisms do not perform photosynthesis, they depend on the chemical energy generated by the plant thanks to sunlight.
The practical result is that the crop obtains a continuous source of nitrogen without needing so many external fertilizers, and some of that nitrogen will remain in the soil when the plant dies or when plant remains are incorporated through agricultural practices. In fact, The decomposition of legume remains significantly enriches the nitrogen content of the soil.
This mechanism explains why legumes are often used in crop rotations or as green manures: they not only produce food, but also help to to improve the fertility of the plot and to support more sustainable farming systems in the medium and long term.
Distribution and diversity of nitrogen-fixing plants
The ecological role of plants associated with nitrogen-fixing bacteria is so important that several scientific teams have studied their large-scale distribution in detail. In the United States, researchers from various centers, such as the Florida Museum of Natural History and the universities of Louisiana and MississippiThey have analyzed records of native and invasive species in dozens of locations to better understand this pattern.
At first glance, one might think that in nitrogen-poor soils there should be greater abundance and diversity of soil-fixing plantssince its competitive advantage would be greater in environments limited by this nutrient. However, detailed analysis significantly qualifies this seemingly logical idea.
When comparing different regions, researchers observed that the number of nitrogen-fixing plants tended to increase in areas with less nitrogen available in the soilThis does fit with the classic hypothesis. But they also observed that, as environments became drier, the overall presence of these plants decreased.
The most striking finding was that, when they looked at the diversity of native nitrogen fixers, they detected a different pattern: The diversity of native soil-fixing species grew remarkably in the arid regionsregardless of the amount of nitrogen present in the soil. That is, where water conditions are harsher, the range of native nitrogen-fixing plants can be very high.
These results show that, on a large scale, the distribution of plants hosting nitrogen-fixing bacteria depends not only on soil nitrogen, but on a complex combination of factors such as water availability, evolutionary history, and the dynamics of plant communitiesUnderstanding these patterns is key to designing agricultural systems better suited to each region.
The role of CBGP: plant biotechnology in the face of climate change
While progress is being made in the ecological understanding of root-fixing plants, research centers such as the Center for Plant Biotechnology and Genomics (CBGP), linked to the Polytechnic University of Madrid, are focusing on another front: adapting crops to the extreme climate we are already experiencing and which will intensify in the coming decades.
Forecasts indicate that by mid-century, approximately 9.700 million people on a planet that is hotter, drier, and subject to much more frequent extreme weather events. The year 2024 was already one of the hottest on record, and in Europe tens of thousands of deaths were linked to heat waves, with Spain being one of the worst affected countries.
Given this scenario, at CBGP they study in a comprehensive way how plants grow, how they interact with the microorganisms in their environment and how they respond to environmental changes such as increased temperature, prolonged drought, or salinization of agricultural soils.
One of the center's main objectives is to develop new crop varieties, or to select from existing ones those that are capable of maintain acceptable yields under environmental stressThis implies not only tolerating adverse conditions, but doing so without depending so much on external inputs such as fertilizers and water.
To achieve this, researchers analyze the molecular mechanisms that allow certain plants to better withstand environmental stresses. They identify defense proteins, signaling pathways, and key genes that are activated under extreme conditions, and use that information to generate what they call "proofs of concept".
In these tests, they create transgenic plants that accumulate certain proteins or activate specific tolerance mechanisms, in order to verify whether they actually improve their performance in the face of drought, heat, or salinity. In this way, They experimentally validate which strategies are most effective. before considering a large-scale application.
More resilient crops: tomatoes, brassicas and food security
One of the outstanding results of this approach has been the development of tomato plants with high salt toleranceThis is an increasingly common problem in agricultural areas where irrigation and intense evaporation concentrate salts in the soil. The CBGP team has developed transgenic varieties that are more resistant to these salt levels.
These hardy tomatoes have already given rise to a European patent applicationThe idea is to extend the technology to other crops that are particularly sensitive to salinity, such as peas, beans, corn, or strawberries. If successful, this would represent a huge advantage in areas where irrigation water is of limited quality or the soils have been degraded.
At the same time, the group is working on transferring these advances to the so-called brassicas, a plant family that includes cabbage, broccoli, and other essential vegetables in the diet. Increasing the resilience of these staple vegetables would mean safeguarding a very important part of food security in an uncertain climate environment.
However, it's not as simple as just introducing defense proteins and that's it. Many of those proteins belong to families that also contain food allergensAnd that makes it necessary to take extra precautions. Not all immune proteins are allergenic, but some can trigger reactions in sensitive individuals.
For this reason, the CBGP has a specialized allergen team that thoroughly evaluates these proteins. Their work focuses on identifying What structural characteristics make a protein a potential allergen? and which ones are not, so that safe biotechnological solutions for human consumption can be designed.
This rigorous approach is essential for innovation in genetically modified or improved crops to have a real place in the market, guaranteeing the food safety and the responsible development of new varieties that help address climate change without creating additional problems.
Towards cereals that “breathe” nitrogen from the air
Among the most ambitious projects being carried out at the CBGP, the one led by the researcher stands out. Luis Rubiofunded by the Gates Foundation. Its goal is as simple to explain as it is difficult to achieve: to make cereals capable of to capture and metabolize nitrogen from the airdrastically reducing dependence on chemical fertilizers.
Unlike legumes, staple crops such as rice, wheat, or corn do not naturally form such powerful symbiotic associations with nitrogen-fixing bacteria. Nor do they possess the internal machinery to fix N₂ on their own, since They lack the nitrogenase enzyme that certain bacteria do possess.
Rubio's team uses as a model a nitrogen-fixing bacterium linked to baker's yeast, known as Azotobacter vinelandii (often misrepresented in some media), capable of fixing nitrogen efficiently. The idea is to transfer the genes involved in nitrogen fixation from these bacteria to plants.
In the laboratory, researchers are working on the introduction and coordinated expression of these bacterial genes in plant cells, with the aim of enabling cereals to internally activate a functional nitrogen fixation systemIt is a huge challenge, because nitrogenase is very complex and extremely sensitive to oxygen, so it requires very specific conditions to function.
If that goal is achieved, even partially, it could represent a revolution for world agriculture: cereals could cover a large part of their nitrogen needs on their own, reducing the use of synthetic fertilizers and, consequently, the soil, water and air pollution associated with its production and application.
Chemical fertilizers and agricultural sustainability
Currently, nitrogen fertilizers are essential to sustain high yields of the global cereal productionThanks to them, it has been possible to feed a constantly growing population, but this dependence has an environmental cost that is increasingly difficult to bear.
The industrial synthesis of fertilizers consumes large amounts of energy and emits greenhouse gases; their intensive use in the field causes air pollution from emissions of nitrogen oxides and ammoniaand runoff carries nitrates to rivers, aquifers and seas, favoring processes such as eutrophication.
In addition, fertilizer overuse and certain management practices can accelerate the degradation of agricultural soilsreducing their capacity to retain water and nutrients and trapping farmers in a vicious cycle of dependence on external inputs.
According to researchers from the self-fertilizing cereals project, a significant decrease in the use of these fertilizers could open the door to a much more sustainable agricultureLess fertilizer means fewer emissions associated with its manufacture, less water pollution, and a greater chance of recovering degraded soils.
The ultimate goal is to develop varieties of rice, wheat, and corn capable of largely self-fertilizeusing nitrogen from the air as the primary source. However, the team itself acknowledges that this is a goal of enormous technological complexity, which will likely require decades of research before being implemented on a large scale in the field.
State-of-the-art infrastructure: greenhouses and rhizotrons
To carry out these projects, the CBGP has facilities of around 1.900 m² dedicated to the cultivation of plants under controlled conditionsA central piece of this infrastructure is a greenhouse of about 1.200 m² equipped with advanced climate control and lighting systems.
These greenhouses allow the cultivation of different species of agricultural interest or experimental models under perfectly regulated conditions of temperature, light, humidity and substrate compositionThis allows for the reproduction of stress scenarios caused by heat, drought, or salinity to evaluate the behavior of modified or selected plants.
The facility features P2-type containment modules specifically designed for working with transgenic plants. Within these spaces, the temperature can be controlled over a wide range, approximately between 10 and 45 ° C, something key to simulating heat waves or moderately cold conditions.
In addition, the greenhouse incorporates a system of automated digital phenotyping with robots that move through the aisles to capture images and data from the plants. This system allows for the precise and large-scale monitoring of aspects such as growth, water status, and the severity of stress symptoms.
Another very interesting element of the infrastructure are the so-called rhizotrons, structures composed of transparent plates that expose the root systemThanks to them, detailed images of the roots can be obtained, their growth and thickness can be measured, and how they respond to different products or environmental conditions can be analyzed.
The combination of these controlled greenhouses, robotic analysis systems, and rhizotrons makes the center an ideal environment for Test new varieties and technologies before scaling up their useFurthermore, these facilities are not reserved solely for internal teams: they are also open to projects from other public and private organizations interested in responding to the agricultural challenges of the future.
All this research on resistance proteins, nitrogen-fixing symbioses, and cereals capable of utilizing atmospheric nitrogen points towards an agricultural model where plants They work more closely with microorganisms and with their own biology. to produce more with fewer external inputs. Although many of these goals will take years or decades to become a reality on a large scale, each advance brings us a little closer to the possibility of crops that, figuratively speaking, “breathe” nitrogen from the air and sustain global food supplies on a planet under climate pressure.
