Biologists at UC San Diego have solved a long-standing mystery concerning the way plants reduce the numbers of their breathing pores in response to rising carbon dioxide levels in the atmosphere.

In a paper published in Nature, they report the discovery of a new genetic pathway in plants, made up of four genes from three different gene families that control the density of breathing pores—or “stomata”—in plant leaves in response to elevated CO2 levels.

Their discovery could help biologists better understand how the steadily increasing levels of CO2 in our atmosphere (which last spring, for the first time in recorded history, remained above 400 parts per million) are affecting the ability of plants and economically important crops to deal with heat stress and drought.

They claimed it could also provide agricultural scientists with new tools to help address the problems heat and drought will cause for current crop plants.

The scientists looked at Arabidopsis, a ‘model organism’ from the mustard family, which is often used in such experiments.

“For each carbon dioxide molecule that is incorporated into plants through photosynthesis, plants lose about 200 hundred molecules of water through their stomata,” explains Julian Schroeder, a professor of biology who headed the research effort. “Because elevated CO2 reduces the density of stomatal pores in leaves, this is, at first sight beneficial for plants as they would lose less water. However, the reduction in the numbers of stomatal pores decreases the ability of plants to cool their leaves during a heat wave via water evaporation. Less evaporation adds to heat stress in plants, which ultimately affects crop yield.”

Schroeder and his team discovered four genes that regulate the development of stomata at elevated CO2 levels. They looked at ways to alter this – abolishing the plants’ response to CO2 Stress. They believe the hormones and proteins identified in their work could be used to look at plants’ response to a higher CO2 future.

Research leader Cawas Engineer said this could lead to "crop varieties which are better able to perform in the current and future high CO2 global climate where fresh water availability for agriculture is dwindling."