CO2 as antifreeze?

CO2 as antifreeze?
January 1, 2001

Plants grow faster. Photosynthesis increases. Root systems improve. Yields jump. Water-use efficiency rises. Drought resistance becomes stronger. Countless stresses are minimized.

An ideal biosphere? Maybe. An attainable one? You bet.

Elevated atmospheric carbon dioxide (CO2) concentrations have netted these benefits again and again, as thousands of articles in major scientific journals attest.

Given the increase in water-use efficiency and tolerance to drier conditions with higher levels of atmospheric CO2, many plant species will be able to survive in marginal drylands in the future where today, various stresses inhibit their survival.

Many of our past essays have dealt with this expected greening up of today’s deserts thereby sequestering additional carbon, improving rangelands in semi-arid areas, and increasing agricultural productivity in arid areas. But as plants extend their habitat into desert areas, they will be forced to cope with a stress often overlooked in dryland areas: freezing temperatures.

Clear desert skies in the winter months may keep the temperatures high in the afternoon, but those same clear and dry conditions allow substantial radiative cooling at night; subfreezing temperatures in deserts are common in winter, and plants in those environments must protect themselves from the cold nights.

An article in a recent issue of the Journal of Arid Environments brings us news of yet another biological benefit of elevated CO2.

A team of biologists from across America grew seedlings of three yucca species all native to the Southwest in controlled-environment glasshouses. Some glasshouses had natural, or ambient, levels of atmospheric CO2 maintained at 360 parts per million (ppm); others at 700 ppm.

They grew plants in various temperature regimes based in part on an analysis of 30 years of temperature records from the yucca’s natural range. But selected plants were placed in coolers, where temperatures were lowered from 20°C to -15°C at a rate of 3°C per hour.

Loik and colleagues discovered, “Plants maintained at elevated CO2 had a greater low-temperature tolerance compared to controls,” results that indicate “survival during episodic subzero temperature events will be enhanced” should CO2 levels increase. They also found that higher “concentrations of CO2 may allow seedlings to have a greater likelihood of surviving lower temperatures and thereby establishing at higher elevations and latitudes in the future.”

We hear (and say) a lot about higher temperatures and CO2; but isn’t it nice to know we can add freeze protection to that long list of biological bonuses from elevated atmospheric CO2?


Robert C. Balling Jr., Ph.D. is director of the Laboratory of Climatology at Arizona State University and coauthor of The Satanic Gases.


Reference

Loik, M.E., et al., 2000. Low temperature tolerance and cold accumulation for seedlings of three Mojave Desert Yucca species exposed to elevated CO2. Journal of Arid Environments, 46, 43-56.