Leaf sizes tied to water availability

Leaf sizes tied to water availability


Posted 12 July 2011, by Jonathan Lebowitz, USA Today, content.usatoday.com

Leaves are some of the most diverse biological objects on the planet and their sizes may be linked to the climates they inhabit.

A study conducted by researchers at the University of California-Los Angeles (UCLA) and published in the journal Plant Physiology now reveals why leaves tend to be smaller in dry climates and larger in wet ones.

To survive, leaves must maintain their “pipe delivery system” to replenish water lost through transpiration, the process plants face when opening their leaf pores to capture carbon dioxide to make sugars for their food.

Occasionally, obstructions in a leaf’s veins, such as an air bubble, blocks water from being “pumped” through the system. These obstructions, known as embolisms, are more likely to occur in the leaves of plants living in climates where water is scarce.

Using three-dimensional computer models, the team of ecologists and botanists simulated the impacts of embolisms on water transport for leaves of different sizes and vein architectures.

“The computer models allowed us to create any type of leaf and introduce any amount of water to identify patterns between an electronic replica and a real laboratory experiment,” says Lawren Sack of the Department of Ecology and Evolutionary Biology at UCLA.

They concluded that the small leaves were better adapted to arid climates, providing more outlets for fresh water to travel into the leaves when “used” water is transpired out of the leaves. Small leaves, like those from desert shrubs, have a greater abundance of “major veins” that provide more pathways around embolisms.

Christine Scoffoni, a doctoral student at UCLA and lead author of the research, compared the major veins to an interstate highway and the minor veins to narrow city roads, where an embolism is like an accident that causes a major slowdown.

Larger leaves, such as those from sunflowers and sycamores, have fewer veins spaced farther apart. Large leaves are well suited for tropical climates where heavy rainfall provides a surplus of water, decreasing the risk for vein network congestion.




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