Will Rising CO₂ Help Fire-Adapted Shrubs Survive Drought? New Research Says Probably Not

By DSE April 23, 2026

Maya Zomer, postdoctoral researcher, is the lead author of a new paper in Tree Physiology examining whether elevated atmospheric CO₂ can protect post-fire seedlings against drought stress in Mediterranean shrublands. Her research was completed as part of her dissertation at the Desertification Research Center (CIDE-CSIC) in Valencia, Spain.

 

The Study

In fire-prone Mediterranean landscapes, many plants rely on germinating from a seed bank after fire, which is known as post-fire seeding. In their first summer, these seedlings face high risk of drought mortality. As climate change intensifies both drought and fire activity, a key open question is whether rising atmospheric CO₂ might offset some of that stress.

 

Higher CO₂ is known to improve water-use efficiency in plants, leading to the hypothesis that future CO₂ conditions could act as a buffer against drought. Maya and her co-authors set out to rigorously test this idea in five Mediterranean shrub species, spanning both non-resprouting seeders (which regenerate exclusively by seed) and resprouting seeders (which can also resprout after fire). These contrasting strategies are linked to distinct drought-related traits, reflecting the range of variation among post-fire seeders in the region.

 

Non-resprouting seeders

From left to right: White-leaved rock rose (Cistus albidus), a five-petaled pink flower with a yellow center; French/Spanish lavender (Lavandula stoechas), with purple flowering tips atop thin green leaves; and Rosemary (Salvia rosmarinus), small violet-colored flowers along a green bushy stem.

Pink flower with a yellow center
purple flowers with green foliage
blue flowers atop bushy green foliage

 

 

 

Resprouting seeders

From left to right: Albaida (Anthyllis cytisoides), a green bushy shrub with yellow flowers; and Prostrate canary clover (Dorycnium pentaphyllum), delicate white flowers with green stems.

green bush with yellow flowers
delicate white flowers with green leaves

 

 

Seedlings were grown for eight months under either ambient (~400 ppm) or elevated (~800 ppm) CO₂, then subjected to a carefully controlled progressive drought, which ranged from well-watered to moderate to intense conditions.

individual red-framed, walk-in boxes where plants are stored underneath a blue sky
Climate-controlled greenhouses used in Maya’s experiment, with three chambers for each CO₂ treatment, at the Centre for Forestry Research and Experimentation (CIEF) in Valencia. Image description: red-framed, walk in enclosures that store plants with bushy green foliage in the background.

 

Key Findings

  • Elevated CO₂ changed plant structure. Plants grown under elevated CO₂ developed denser leaves and, in three species, greater above- and belowground biomass. 
  • CO₂ did not improve drought stress or modify plant water relations. Elevated CO₂ had no measurable effect on water status or hydraulic behavior under drought, at either the species level or when comparing resprouting vs. non-resprouting groups.
  • Resprouting ability shaped how plants responded to drought. Resprouting seeders maintained more stable water potentials as drought intensified, while non-resprouters held higher water potentials under mild and moderate drought but showed steeper declines under severe stress (a pattern independent of CO₂ treatment).

 

box chart of findings
Leaf midday water potential, a measure of plant dehydration stress, was largely unaffected by CO₂  treatment (ambient vs. elevated), but resprouting seeders (R+) maintained more stable water potentials under drought regardless of CO₂ level. Image description: three color-coded box plots showing results from Maya's study.

 

Reflections

This experiment was among the most demanding of Maya's PhD. The team built CO₂ greenhouses from scratch, then weighed and hand-watered 140 large plant pots every day throughout the three-month drought experiment, much of which coincided with the COVID pandemic shutdown in spring 2020.

 

Overall, findings suggest that elevated CO₂ is unlikely to meaningfully reduce drought risk for post-fire seeders as the climate changes. Moreover, a species' life history strategy, including whether or not it can resprout after fire, is a critical factor in predicting how it will fare in a more fire-prone and drier world.

 

"Not all plants will respond to rising CO₂ in the same way," said Maya. "We need to account for these differences when modeling plant water use, drought mortality, and fire dynamics under global change."

 

 

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