Reversing desertification and regreening Saudi Arabia while aiming for a carbon neutral economy by 2060 seems ambitious. Plant scientist Heribert Hirt believes it can be done, provided there is a true collaborative spirit among all involved. Two large-scale projects at KAUST are contributing significant new information about desert and mangrove plants, as well as the microbial communities in the soils that support them. This, says Hirt, lies at the heart of making a reality of Saudi’s Green Initiative and the Saudi 2060 vision of net zero carbon.
The Saudi Green Initiative aims to plant 10 billion trees in the country with the goal of reversing desertification. KAUST’s plant scientists are working on the sustainability strategy for this initiative.
“It is critical to use the right plants under an appropriate planting system, otherwise they will simply die,” says Hirt. “Many greening efforts have failed because the wrong trees have been planted or the soils are so depleted in nutrients that they cannot sustain growth.”
Planting imported trees is not appropriate. In fact, Hirt and his team believe that trees are not the best option for a desert greening project; they would rather focus on planting shrubs, at least to begin with. Shrubs achieve the same goal of stabilizing and replenishing soils but require less water and have far greater chance of survival.
Desertification is a dynamic, ongoing process that is largely fueled by the overgrazing of animals. Grazing interrupts the growing cycle of plants whereby the plants fail to propagate because they are eaten before they can produce seed.
“Greening efforts have failed because the wrong trees have been planted or the soils are so depleted in nutrients.”
“Soil is fed by plants. If you have no vegetation, you cut out the food for soils, and you also lose the soil’s microbial life, which aggravates the problem,” says Hirt. “We know comparatively little about soil profiles and microbial populations in hyperarid regions; soil science research has largely been conducted in temperate zones. Soil science in arid regions is deservedly an active area of research now.”
Hirt’s team is creating a soil atlas for Saudi Arabia. The country has a large land area and encompasses a huge variety of ecosystems and climatic zones with many different soil types.
“You cannot just study the plants on their own – they have co-evolved with microbes from the environment and require these symbionts to survive,” says Hirt. “Knowledge of both soil and microbial structures is vital to ensure the success of the Saudi Green Initiative.”
The team has compiled the world’s largest biobank of desert microbes, and each microbe’s genome has been sequenced. Hirt’s dream is that this biobank can be used to complement missing microbes — ones that should be there but have been depleted or lost entirely.
“This opens doors to a natural way of regenerating soils: by replacing components that have been lost,” says Hirt. “To do this effectively, we need the help of AI. Human brains are brilliant, but they do not have the speed or computational power of machine learning algorithms.”
Each plant has around 25,000 genes and hosts a microbiome of approximately 1,000 different species. Each microbial species has around 4,000 genes it can contribute to the plant. “That’s over 425,000 genes for each plant, and each gene has a role to play,” says Hirt.
“Our AI algorithm aims to generate a metabolic map of each halobiont (plant and microbes working together) and predicts the function of each gene. We can then add the missing components from a particular soil to help a specific plant to thrive.”
Another critical ecosystem in need of regeneration is Saudi’s mangrove swamps. Mangroves form a highly diverse unique boundary ecosystem in the inter-tidal zone, but many have been destroyed to make way for people to live and work along the coast. Mangroves are now recognized as vital, not just as ecosystems but as carbon stores and for their role in limiting greenhouse gas emissions.
“Without mangroves, the microbial communities in this intercoastal region produce extensive amounts of nitrous oxides and methane — two of the worst greenhouse gases,” says Hirt. “While mangroves are brilliant at capturing CO2, they are even better at preventing microbes from releasing methane into the air.”
Mangrove plants are part marine, part terrestrial, making them a rich source of unique microbes. Some of these microbes could be used to counter the effects of climate shifts around the world, such as flooding.
“Microbes could be used to counter the effects of climate shifts around the world, such as flooding.”
“Mangroves host microbial communities that can help plants survive flooding – we have had amazing results in experiments with rice at KAUST,” says Hirt. “We can also encourage rice to grow faster by boosting its microbial symbionts, potentially enabling an additional harvest per year in tropical climates; this could feasibly transform global food supplies.”
Boosting plant growth and ecosystems across the country will undoubtedly help sequester carbon, a key aim of the Saudi 2060 mission. Hirt and his team have recently uncovered an unexpected metabolic trait in desert plants and associated microbes that could lock carbon away for centuries.
“Plants remove a certain amount of carbon from the air via photosynthesis, some of which is filtered to soil microbes,” says Hirt. “Certain microbes working with these plants can turn part of the carbon into calcium carbonate – a very stable and safe way to sequester carbon for decades or even centuries. If we can convince the world’s arid nations to invest in planting the right plants with the right microbes in the right soils, it will be a game changer.”
Proposed taxes on high CO2 producers could potentially pay for this system to be harnessed in full, notes Hirt, particularly as many of the world’s arid regions are also the poorest.
“Everything is there to develop this idea, we just need to understand how to put the pieces together,” says Hirt. “It’s time to work closely together to solve some of the world’s most challenging problems.”