Increasing temperatures puts desert bushes in high efficiency mode

Death Valley doesn’t seem like the most ideal place to resist rising temperatures amid changing weather. But for the desert plants that live there, it is their home, and they face the option of adapting or dying.

Research from the University of Utah shows that one bush, the brittlebush, is adapting and showing remarkable ability to respond to increased temperature and aridity. The research is published in procedures of the National Academy of Sciences and it was funded by the National Science Foundation.

“We were able to directly relate changes in plant ecophysiology to climate change in a relatively short period of time,” says study lead author and laboratory technician Avery Driscoll. “This shows us that desert shrubs can and do acclimate to changing environmental conditions.”

Forty years in the desert

The data for this study comes from two long-term research sites in the remote deserts of the American Southwest, one in Death Valley and the other near Oatman, Arizona, both with an area of ​​a few hundred square meters. The sites were established in the early 1980s by distinguished biology professor U Jim Ehleringer, who recognized both the value of long-term observations and the appeal of traveling somewhere warm during the cold months of Salt Lake City. Every spring for almost 40 years, Ehleringer and members of his laboratory have visited the research sites to study vegetation and collect plant samples for further analysis.

In 2020, a reduced and postponed survey trip was still conducted. “Easy to get away when working in the Mojave Open,” co-author Darren Sandquist tweeted.

The study focuses on a particular shrub species: Encelia farinosa, also called brittlebush or incense. It can live for over 30 years and is widely found throughout southwestern and northern Mexico, with bright yellow flowers and silvery leaves.

Biologists who study forests have an easily accessible climate record in tree rings. But in environments with few trees, they need another method. Brittlebush leaves, collected over time, contain their own climate record on the carbon isotopes that make up the leaf tissue. Isotopes are atoms of the same element that differ in weight by only one or two neutrons. Many isotopes are stable, that is, non-radioactive, and their slight difference in mass can be reflected in physical or physiological processes.

In this case, the carbon isotopes in the brittlebush leaves reflected how wide the plants were opening their stomata, small pores on the underside of their leaves. Plants open stomata to absorb more carbon dioxide, but at the risk of losing water vapor. Therefore, isotopes can generate the efficiency of the plant’s water use or the balance between the amount of water lost and the rate of photosynthesis.

Adapt to efficiency

Results show that brittle shrubs increased water use efficiency by 53-58% during the 39-year study period. That is remarkably high, almost double the increase in forest efficiency over the same period of time.

The temperature is increasing and the humidity is decreasing in the Mojave Desert, Driscoll says. “This increase in water use efficiency shows that the physiology of the leaves of these plants has been adjusted in response to this additional water stress and increased availability of CO_two“

Researchers have proposed that increasing CO_two levels can be beneficial for plants like brittlebush, allowing you to get the same amount of CO_two with smaller stomatal openings, reducing water loss So far, however, forests have not shown increased growth coupled with greater water use efficiency.

“While we can’t say anything about the implications for shrub growth,” says Driscoll, “we found that increases in water use efficiency were substantially greater in deserts than in forests.”

The researchers observed greater water use efficiency in some plants that had been sampled throughout the entire study period, showing acclimatization by individuals, as well as the entire shrub population, to changing conditions.

These shrubs can have a lifespan of more than 30 years and new plant establishment occurs infrequently, “Driscoll says,” so we cannot rule out the possibility of generational changes also if populations are observed at longer times. “

So does this finding mean brittlebush and other desert shrubs will be able to withstand future warming? We still can’t say, Driscoll says.

“While more efficient use of water may translate into growth, survival, or flowering benefits for these plants, we do not yet know whether the change will confer advantages or mitigate potential population declines.”