Researchers at King Abdullah University of Science and Technology have developed a new method to capture carbon dioxide using plants and microbes that produce oxalates. With this they aim at converting deserts into carbon sequestration systems. To put things into action, the team began experiments in northwestern Saudi Arabia. They planted nitrogen-fixing legumes, such as acacias, to help desert plants grow.
Cutting down emissions is alone not effective to reduce the extreme CO2 levels present in the atmosphere. We need to remove the already present concentrations of carbon dioxide in the environment and store it. A team of plant scientists from King Abdullah University of Science and Technology (KAUST) recently published an opinion paper stating that arid lands have the potential to capture carbon dioxide.
According to the researchers, it is possible to transform an arid ecosystem into effective carbon sequestration systems. This could be possible by improving soil health, enhancing photosynthesis efficiency, and increasing root biomass. And this can be achieved by engineering ideal combinations of soil microbes, soil type, and the right combination of plants to incorporate and promote a naturally occurring biogeochemical process. Oxalate-carbonate pathway is the process being discussed here which will help in creating carbon sinks underground.
Heribert Hirt, senior author and plant scientist at KAUST, said, â€œRe-greening deserts by restoration of ecosystem functions, including carbon sequestration, should be the preferential approach. The advantage of reclaiming arid regions for re-greening and carbon sequestration is that they do not compete with lands used in agriculture and food production.â€
Importance of Oxalates
The method takes advantage of arid-adapted plants that produce oxalatesâ€”ions containing carbon and oxygen that are associated with kidney stones or gout. Certain soil microbes rely solely on oxalates as their carbon source. As a result, they release carbonate molecules into the soil.
Carbonate often decomposes rapidly, but when these plant-microbe systems are cultivated in soils that are alkaline and rich in calcium, the carbonate interacts with calcium to create enduring calcium carbonate deposits.
The natural carbon cycle usually involves the exchange of carbon dioxide between the atmosphere, oceans, and terrestrial ecosystems. However, due to human activities, there has been a significant build-up of excessive CO2 in the atmosphere.
Trees Vs. Arid Lands
Trees are often seen as the perfect solution for capturing carbon, yet the challenge is that reforestation often competes with agriculture for valuable arable land. But converting deserts into carbon sequestration systems is a new concept. There is a vast opportunity in arid lands, which make up about one-third of the Earth’s surface and are currently not utilized for agriculture.
Arid ecosystems are known for their limited plant life, primarily due to the scarcity of water. Certain plants have ingeniously developed various strategies to survive in these challenging conditions, successfully overcoming the scarcity of water and extreme temperatures.
Certain plants that thrive in arid conditions possess remarkable root systems for accessing underground water sources. In addition, they utilize distinct forms of photosynthesis that enable them to conserve water during scorching periods of the day.
Then there are also plants known as oxalogenic with the ability to produce substantial quantities of oxalates, which can be transformed into water during droughts.
Microbes not only utilize carbon for their own metabolism, but also release it as carbonate into the soil. This carbonate has the ability to precipitate as calcium carbonate, and its stability can endure for several centuries or even millennia. The proposed system for carbon sequestration on arid lands involves a combination of oxalogenic plants, which release up to one-quarter of their carbon as oxalic acid into the soil, and oxalotrophic microbes.
From these oxalates, some amount of carbon is deposited underground, and the team wants to use this mechanism for carbon sequestration. According to the report, “Overall, in this form of carbon sequestration, one out of every sixteen photosynthetically fixed carbon atoms might be sequestered into carbonates.”
According to the authors, by enhancing this biogeochemical process that occurs naturally in arid lands, it is possible to transform these unproductive and degraded ecosystems into carbon sinks with thriving soil and plants.
The authors suggest that fertility islands should be taken as the starting point. They are small areas of revitalized habitat from which plants and microbes can expand, eventually creating a lush carpet of vegetation.
Co-author Hassan Boukcim has already started experiments in northwestern Saudi Arabia, planting nitrogen-fixing legumes like acacias to support the growth of other desert plants. The authors believe that these approaches could lead to big increases in the amount of carbon stored in plants and soil within ten years.
However, they point out that the success and speed of this method will be influenced by the rate at which plants grow in dry conditions, as well as the availability of funds and political support in different arid countries.
â€œAs part of KAUST’s Native Genome Project, we have already identified some native oxalogenic plant species, but this project is going to be extended now to characterize hundreds of native plants and microbes,â€ says Professor Hirt.
Professor Hirt’s team has revolutionized the process of seed coating by applying beneficial microbes directly onto native plant seeds. These seeds are carefully cultivated in nurseries before being planted in harsh desert environments. So, converting deserts into carbon sequestration systems may seem an unachievable task, but it is better to try different approaches rather than nothing.