(CN) — Like countless other living things on Earth, plants have a remarkable ability to adapt to changes in their environment in a bid for survival. One way plants do this is by changing the size of their stomata, a series of openings on plant leaves that dictate how much carbon dioxide comes in and how much water vapor goes out.
This ability gives plants a metric known as intrinsic water-use efficiency, or iWUE, which measures the amount of photosynthesis in a plant against the openness of the stomata. When plants experience a rise in temperature or if water becomes scarce, the plant can crank up their iWUE by restricting the openings of their stomata to keep in as much water as possible.
Armed with this knowledge, a team of researchers from the University of Utah explored decades of data to see how desert shrubs have adapted their iWUE in response to historic drought conditions across the Southwest. In a study released Monday in Proceedings of the National Academy of Sciences, they reveal that while these plants have been putting in the effort to keep up, it may not be enough.
For the last 40 years, University of Utah scientists have made the trek to the Mojave Desert every March to collect samples of shrub leaves. Jim Ehleringer began the tradition not only to escape to somewhere warm during the winter, but also because published data on iWUE trends in the Southwest have proven virtually nonexistent, forcing researchers to build their database from scratch over nearly half a century.
“Unfortunately, there are almost no published long-term records of iWUE in the Southwest,” Steven Kannenberg, postdoctoral research associate in the U’s School of Biological Sciences, said with the release of the study. “Additionally, the vast majority of long-term data are on trees, so the sensitivity of iWUE in other plant types is unknown.”
Once they had enough data, experts studied the leaves’ stable isotopes, a series of chemical signatures that can help paint a picture on how the plants have managed their internal water economy over the years.
What they found in that data surprised the researchers. They had assumed the shrubs’ iWUE would have increased but would also level off over time.
Instead, they found the plants’ iWUE rates skyrocketed to almost historic levels. When compared to data taken from other plants in other desert locations, the shrubs in the Mojave increased their iWUE six to ten times faster than their fellow desert brethren.
The increase was so tremendous that researchers only found one recorded instance of a plant experiencing a bigger boost — in a conifer.
While these increases astounded the researchers, they said they remain skeptical they will be enough to save the shrubs. The Southwest has been experiencing one of the worst megadroughts in the past 1,200 years, and most forecasters agree it will intensify. Ultimately, researchers warn, it could be a tight race to see if the historic drought can endure longer than the shrubs’ ability to adapt.
“The Southwest is in a really dry period,” Kannenberg said, “and this is further evidence of how much the ‘megadrought’ has impacted plant functioning and how anomalous this period is.”
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