As the imperative to reduce atmospheric CO2 levels intensifies, scientists are exploring innovative strategies to capture and store excess carbon emissions. In an opinion paper published in the journal Trends in Plant Science, a team of plant scientists proposes an unconventional solution—transforming arid lands, such as deserts, into efficient carbon-capture systems.
Led by senior author and plant scientist Heribert Hirt of King Abdullah University of Science and Technology, the research team outlines a visionary approach that leverages improved soil health, enhanced photosynthetic efficiency, and increased root biomass to facilitate a naturally occurring biogeochemical process known as the oxalate-carbonate pathway. By engineering ideal combinations of plants, soil microbes, and soil types, they aim to create below-ground carbon sinks in arid ecosystems.
The authors argue that “re-greening” deserts by restoring ecosystem functions, including carbon sequestration, should be a preferred approach. This strategy could potentially mitigate the excess carbon in the atmosphere while bypassing competition with agricultural and food production lands.
The proposed method capitalizes on the unique capabilities of arid-adapted plants that produce oxalates, compounds containing carbon and oxygen. Some soil microbes rely on oxalates as their primary carbon source and, in doing so, release carbonate molecules into the soil. While carbonate is typically short-lived, when these plant-microbe systems thrive in alkaline and calcium-rich soils, carbonate reacts with calcium to form stable deposits of calcium carbonate.
Carbon naturally cycles between the atmosphere, oceans, and terrestrial ecosystems, but human activities have disrupted this balance, resulting in the accumulation of excess CO2 in the atmosphere. Even with efforts to reduce CO2 emissions, the authors stress that the climate effects of elevated CO2 will persist for centuries unless atmospheric CO2 can be effectively sequestered.
While trees are often seen as ideal for carbon capture, reforestation competes directly with agriculture for arable land. In contrast, arid lands, constituting roughly one-third of terrestrial surfaces, are currently underutilized for agriculture due to their extreme aridity.
Arid ecosystems typically support limited plant life due to water scarcity, but some plants have evolved mechanisms to adapt to these challenging conditions. Certain arid-adapted plants possess specialized root systems that reach deep into the soil to access hidden water sources, while others employ alternative forms of photosynthesis to minimize water loss during extreme heat.
One group of arid-adapted plants, termed “oxalogenic” plants, produces significant quantities of oxalates. During droughts, they can convert these oxalates into water and deposit some of the carbon below ground as stable carbon deposits. This natural biogeochemical process is what the authors aim to harness for carbon sequestration.
In this form of carbon sequestration, approximately one out of every 16 photosynthetically fixed carbon atoms can be transformed into carbonates, according to the authors.
The researchers propose initiating the process by establishing “fertility islands”—small patches of re-greened habitat that serve as starting points for the proliferation of plants and microbes. Over time, these islands could expand to form extensive carpets of vegetation, converting unproductive and degraded arid ecosystems into robust carbon sinks with healthier soil and plant life.