Why juniper trees can live on less water(ylem tissues under a partial vacuum so ...)

The scientists found that xylem tissues of juniper species tend to be reinforced with extra woody material to prevent rupture. Such rupturing can introduce bubble-forming air either through seepage from adjacent cavities or by coming out of solution from the water itself, Jackson said.

The scientists also determined that the more cavitation-resistant Juniper species have thicker but narrower leaves -- a trait known as low specific leaf area (SLA) -- and live primarily in the western United States.

"Plants in drier environments typically have lower SLA," said Willson, the study's first author, who having completed her Ph.D. at Duke is now a student at North Carolina State University's College of Veterinary Medicine. "We found that junipers from the driest environments were more drought resistant and also had the lowest SLA."

Their research found that the most cavitation-resistant species is the California juniper, which grows in California's Mojave Desert, while the least resistant is the eastern red cedar -- the most widespread conifer in the relatively-moist eastern U.S.

While less drought-tolerant than other junipers, eastern red cedars still handle dry spells well and are in fact invading into Midwestern states including Nebraska, Jackson noted. Juniper species growing in wet parts of the Caribbean also benefit from drought tolerance because they "tend to grow in shallow, rocky soils that don't hold a lot of water," Jackson said.

In parts of the Southwest undergoing an extended drying period, junipers are edging out another hardy, water-thrifty conifer -- the pinyon pine. "They're both very drought- resistant, but the pinyons aren't as resi
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