Rising temps put desert shrubs in high-efficiency mode
Long-term observations track Mojave Desert plants' responses to climate
change

Date:
July 27, 2020
Source:
University of Utah
Summary:
Research shows that one shrub, the brittlebush, is adapting, and
showing a remarkable ability to respond to increased temperature
and aridity.



FULL STORY ========================================================================== Death Valley doesn't seem like the most ideal place to ride out rising temperatures amid a changing climate. But for the desert plants that
live there, it's home -- and they face the choice to adapt or die.


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

"We were able to directly relate changes in plant ecophysiology to
changing climate over a relatively short timescale," 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 Data for this study came 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 U distinguished professor of biology Jim Ehleringer, who recognized
both the value of long-term observations, and the appeal of traveling
somewhere warm during Salt Lake City's cold months. Every spring for
nearly 40 years, Ehleringer and members of his lab have visited the
research sites to survey the vegetation and collect samples of plants
for later analysis.

In 2020, a scaled-down and postponed survey trip still went forward. "Easy
to distance when working in the wide-open of the Mojave," tweeted
co-author Darren Sandquist.



==========================================================================
The study focuses on one shrub species in particular: Encelia farinosa,
also called brittlebush or incienso. It can live more than 30 years and
is found widely throughout the Southwest and northern Mexico, with bright yellow flowers and silvery leaves.

Biologists who study forests have a readily 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
in the isotopes of carbon that make up the leaf tissue. Isotopes are atoms
of the same element that differ in weight by only a neutron or two. Many isotopes are stable, i.e. non-radioactive, and their slight difference
in mass can be reflected in physical or physiological processes.

In this case, the isotopes of carbon 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 take in more carbon
dioxide, but at the risk of losing water vapor. So the isotopes can yield
the plant's water use efficiency, or the balance between the amount of
water lost and the rate of photosynthesis.

Adapting for efficiency The results show that the brittlebushes increased
their water use efficiency by 53-58% over the 39-year study period. That's remarkably high, nearly double the increase in efficiency in forests
over the same time period.



========================================================================== Temperature is rising and humidity is decreasing in the Mojave Desert,
Driscoll says. "This increase in water-use efficiency shows that the leaf physiology of these plants has adjusted in response to this added water
stress and increased availability of CO2." Researchers have proposed that increasing CO2 levels may be a benefit to plants like the brittlebush,
allowing it to get the same amount of CO2with smaller stomatal openings, reducing water loss. So far, though, forests haven't demonstrated an
increase in growth along with an increased water use efficiency.

"While we can't say anything about the implications for shrub growth,"
Driscoll says, "we did find that increases in water-use efficiency
were substantially larger in deserts than they are in forests."
The researchers observed increased water use efficiency in some plants
that had been sampled throughout the entire study period, showing
acclimation by individuals, as well as by the whole shrub population,
to changing conditions.

These shrubs can have lifespans of 30+ years and establishment of new
plants occurs infrequently," Driscoll says, "so we can't rule out the possibility that generational changes will also occur if the populations
are observed over longer timescales." So does this finding mean that
the brittlebush and other desert shrubs will be able to weather future
warming? We can't yet say, Driscoll says.

"While it's possible that more efficient use of water could translate
into growth, survival or flowering benefits for these plants, we don't
yet know if the change will confer advantages or mitigate potential
declines in the population."

========================================================================== Story Source: Materials provided by University_of_Utah. Original written
by Paul Gabrielsen.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Inaugural Article avery W. Driscoll, Nicholas Q. Bitter, Darren R.

Sandquist, and James R. Ehleringer. Multidecadal records of
intrinsic water-use efficiency in the desert shrub Encelia
farinosa reveal strong responses to climate change. PNAS, 2020 DOI:
10.1073/pnas.2008345117 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200727154204.htm

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