We’ve all learned the same story in school: plants breathe in carbon dioxide (CO₂) through their leaves during photosynthesis, and breathe it out through respiration. The roots? They’re just for water and nutrients, right?
Think again.
In a surprising twist to one of biology’s most fundamental processes, a new study published on October 17, 2025, in the open-access journal Carbon Research has revealed that plant roots can actively absorb CO₂ from the soil—and this hidden process is powerfully influenced by light, fertilizer, and atmospheric conditions.
Led by Dr. Amiran Khabidovich Zanilov at the Center for Decarbonization of the Agro-Industrial Complex and Regional Economy, Kabardino-Balkarian State University Named After H.M. Berbekov, this innovative model experiment is rewriting the textbook on how plants feed themselves—and offering fresh insights into the global carbon cycle.
A New Window into Plant Breathing
To crack the mystery of root-level CO₂ dynamics, Dr. Zanilov and his team designed a custom experimental system with hermetically sealed chambers for both leaves and roots, equipped with high-precision CO₂ sensors. This allowed them to track CO₂ fluxes in real time across the entire soil–plant–atmosphere continuum—a rare feat in plant physiology research.
Using 19 maize plants over a 40-day period, they tested four distinct environmental scenarios, each designed to mimic real-world changes in farming and climate.
Light Switches On a Hidden Root Mechanism
In Mode A, the team explored how day-night cycles affect CO₂ exchange. What they found was striking: as daylight ended and photosynthesis paused, CO₂ concentrations in the leaf chamber rose, while those in the root chamber dropped sharply—revealing an inverse correlation (r = -0.859).
This means that when leaves stop absorbing CO₂, roots kick in, potentially scavenging carbon directly from the soil air. Even more fascinating: root CO₂ uptake peaked during daylight when atmospheric CO₂ reached 367–417 ppm—levels eerily close to today’s real-world concentrations.
“This suggests that root-based CO₂ absorption isn’t just a curiosity—it may be an alternative carbon nutrition pathway,” says Dr. Amiran Khabidovich Zanilov. “When light is abundant, roots might help buffer or supplement carbon supply, especially under fluctuating atmospheric conditions.”
Fertilizer’s Double-Edged Effect
In Mode B, the researchers introduced ammonium nitrate fertilizer—a common practice in modern agriculture. But instead of boosting carbon uptake, the results showed a short-term setback: leaf respiration increased at night, and daytime CO₂ absorption dropped significantly, from 70.4 ppm to 92.3 ppm compared to unfertilized plants.
“The nitrogen boost comes at a cost,” explains Dr. Zanilov. “It appears to shift the plant’s energy balance, increasing metabolic activity but temporarily reducing its ability to fix carbon during the day. Farmers may need to consider timing and dosage to avoid undermining photosynthetic efficiency.”
Brighter Light, Slower Shutdown
Mode C tested how light intensity affects plant behavior. When illumination doubled—from 1750 to 3500 lux—something unexpected happened after lights-out: the leaves didn’t start respiring immediately. Instead, there was an 80-minute delay before CO₂ began to rise in the leaf chamber.
This lag suggests that high-light-grown plants store more energy or carbon intermediates, allowing them to maintain internal balance longer once photosynthesis stops. It’s like a battery charge that keeps the lights on a little longer after sunset.
When the Air Gets Thick: Roots Shut Down
Finally, in Mode D, the team simulated rising CO₂ levels—such as those caused by intense soil microbial activity or climate change. As CO₂ in the leaf chamber climbed from 500 to 1500 ppm, something dramatic occurred: root CO₂ absorption stopped completely.
At high atmospheric CO₂, the concentration gradient reverses, making it harder for roots to take up gas from the soil. This could mean that in a future high-CO₂ world, this newly discovered root carbon pathway may become less effective—unless plants adapt.
Why This Changes Everything
For decades, scientists assumed that plant roots were net producers of CO₂ through respiration, not consumers. This study challenges that view, showing that under normal conditions, roots can act as carbon sinks, not just sources.
These findings have profound implications:
For ecology, as we rethink how plants interact with soil carbon in forests, wetlands, and croplands.
For climate models, which must now account for potential root-level CO₂ uptake in terrestrial carbon budgets.
For agriculture, where optimizing light, fertilizer, and soil conditions could enhance carbon capture and crop resilience.
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