Plants are the natural allies of humans in the battle against global warming. They absorb carbon dioxide from the atmosphere and use it to grow and produce oxygen. But what if plants could do even more to help reduce the greenhouse effect?
A new study suggests that improving air quality could boost the ability of plants to sequester carbon and mitigate climate change.
The link between air pollution and photosynthesis
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The study, published in the journal Trends in Plant Science, used a computer model to estimate how much photosynthesis has increased globally since the Industrial Revolution.
The researchers found that photosynthesis has increased by 30%, mainly due to the rising levels of carbon dioxide in the air, which acts as a fertilizer for plants.
However, the study also found that another factor that affects photosynthesis is air pollution.
Specifically, the researchers focused on aerosol particles, which are tiny solid or liquid droplets suspended in the air.
Aerosols can come from natural sources, such as dust, sea salt, and volcanic eruptions, or from human activities, such as burning fossil fuels, agriculture, and industry.
These can have both positive and negative effects on photosynthesis, depending on their size, composition, and location.
On the one hand, aerosols can scatter and reflect sunlight, reducing the amount of light that reaches the plants. This can limit the rate of photosynthesis and the growth of plants.
On the other hand, aerosols can also cool the climate by reflecting some of the incoming solar radiation back to space. This can benefit plants by reducing the stress caused by high temperatures and water loss.
Aerosols can also increase the diffuse fraction of sunlight, which is the portion of light that reaches the plants from all directions, rather than directly from the sun. This can enhance photosynthesis by allowing more light to penetrate deeper into the plant canopy and reach more leaves.
The net effect of aerosols on photosynthesis depends on the balance between these positive and negative effects, which can vary by region and season.
The researchers estimated that reducing aerosol pollution would increase the amount of sunlight available for plants by 0.5% to 2.5%, depending on the location.
This would result in an increase of photosynthesis by 0.2% to 1.4% and an increase of carbon sequestration by 0.1% to 0.7%.
Carbon sequestration is the process of capturing and storing carbon in long-term reservoirs, such as soils, rocks, or oceans.
Carbon sequestration by plants is a natural and cost-effective way of removing carbon dioxide from the atmosphere and reducing its concentration.
Plants sequester carbon in two ways: by storing it in their biomass (such as stems, leaves, and roots), and by transferring it to the soil through litterfall, root exudates, and decomposition.
The researchers estimated that the current global carbon sequestration by plants is about 3.1 gigatons of carbon per year, which is equivalent to about 29% of the human-caused carbon emissions.
By improving air quality and increasing the sunlight available for plants, the researchers projected that the carbon sequestration by plants could increase by 0.03 to 0.21 gigatons of carbon per year, which is equivalent to about 0.3% to 2% of the human-caused carbon emissions.
While this may seem like a small increase, the researchers pointed out that it is comparable to the carbon sequestration potential of other proposed solutions, such as reforestation, bioenergy, and biochar.
Moreover, the researchers emphasized that improving air quality would have multiple benefits for human health, biodiversity, and ecosystem services, in addition to enhancing carbon sequestration by plants.
The researchers also suggested that some regions could have higher potential for carbon sequestration by plants than others, depending on the local climate, vegetation, and soil conditions.
For example, they highlighted that arid lands, which cover about one-third of the terrestrial surface, could be transformed into efficient carbon sinks by engineering ideal combinations of plants, soil microbes, and soil type to facilitate a naturally occurring biogeochemical process called the oxalate-carbonate pathway.
This process involves the production of oxalates by some plants, which are then consumed by some soil microbes, which in turn excrete carbonates that react with calcium to form stable deposits of calcium carbonate in the soil.
The researchers concluded that improving air quality could be a win-win strategy for enhancing natural carbon sequestration by plants and mitigating climate change.
They called for more research and policy support to explore the feasibility and effectiveness of this approach, and to integrate it with other measures to reduce greenhouse gas emissions and adapt to the changing climate.
