With much of the Southeastern U.S. beset by drought, a team of Duke biologists has been studying one particularly drought-resistant plant: the juniper.
The team, led by Robert Jackson, a professor of global environmental change and biology at the Nicholas School of the Environment and Earth Sciences, has examined fourteen species of juniper from the U.S. and the Caribbean, and found that even those species that thrive in the mountains of Jamaica and generally get hundreds of inches of rain each year have evolved to do without.
Junipers' ability to thrive in drier climates appears to stem from a key structural adaptation-a resistance to "cavitation," the tendency for air bubbles to form in plants' xylem tissues, which are responsible for carrying water from the roots up through the leaves.
In particularly dry situations, cavitation can cause a plant to dry out and die. Jackson's team found that junipers' xylem tissues tend to be reinforced with extra woody material that prevents them from rupturing and letting in air bubbles.
Juniper populations have been expanding for the last 100 years in some places, "and drought plays a role in that," Jackson says. "For example, recent droughts have decimated pinyon pine populations in pinyon-juniper woodlands of the Southwestern U.S. but left the junipers relatively unscathed."
The scientists found that the most cavitation-resistant species of juniper is the California juniper, which grows in California's Mojave Desert; the least resistant is the eastern red cedar, the most widespread conifer in the relatively moist eastern U.S.
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 says. The research team's report was published online in the American Journal of Botany. Cynthia Willson Ph.D. '06 was lead author of the report.