The size of leaves can vary by a factor of 1,000 across plant species, but until now, the reason why has remained a mystery. A new study by an international team of scientists led by UCLA life scientists goes a long way toward solving it.
In research federally funded by the National Science Foundation, the biologists found that smaller leaves are structurally and physiologically better adapted to dry soil because of their distinct vein systems.
The research will be published in an upcoming print issue of the journal Plant Physiology and is currently available in the journal's online edition.
"A hike in dry areas, such as the Santa Monica Mountains, proves that leaves can be small. But if you are in the tropical forest, many leaves are enormous," said Lawren Sack, a UCLA professor of ecology and evolutionary biology and senior author of the research.
This biogeographic trend smaller leaves in drier areas may be the best recognized in plant ecology, true at both the local and global scales, but it had evaded direct explanation, Sack said.
Sack and his research team focused on deciphering the meaning of the huge diversity in the patterns of veins across plants. They found that small leaves' major veins those you can see with the naked eye are spaced more closely together and are of greater length, relative to the leaf's size, than those of larger leaves.
This redundancy of major veins, the researchers say, protects the leaves from the effects of embolism bubbles that form in their "water pipes" during drought because it provides alternate routes for water to flow around vein blockages.
"Even with strong drought that forms embolism in the veins, a small leaf maintains function in its vein system and can keep functioning for water transport," Sack said.
"Unlike people, plants don't seem to have a complex hierarchy of needs give them sun, water and nutrients, and they
|Contact: Stuart Wolpert|
University of California - Los Angeles