Source Pravda.Ru

Trees cannot exceed the limit-Study

Life is tough at the top, especially for very large trees. The tallest tree on the planet, a giant redwood that soars 370 feet into the California sky, is still growing.

But scientists say it will not grow higher than 130 meters because the taller a tree gets, the more difficult it is for water to get to the top.

"The taller trees grow, and they do that because they are competing with other trees for light, the less able they are to grow taller," George Koch, a physiological ecologist at Northern Arizona University in Flagstaff, told Reuters.

According to newsday.com for the world's tallest trees, a bit more sky is apparently the limit, as new research on California's giant redwoods concludes that a height of 400 to 427 feet is absolute tops.

The researchers also examined three other physiological and functional features, which all supported the same conclusion: tree height is limited by increasing water stress in leaves, a consequence of the downward pull of gravity fighting the upward pull of water through the tree's transportation system. The leaf adaptations apparently serve as a trade-off to protect the trees from air bubbles that can block a tree branch's transporting cells in a process known as cavitation, comparable to injecting air bubbles into a garden hose.

"The leaves at the top, because they are water-stressed, are not doing as much photosynthesis per unit mass," said Professor Koch, who is a physiological ecologist.

"In essence, the plant is investing a certain amount into those tissues but they're not providing as much return on that investment because of the water stress."

Conditions at the redwoods' tops are similar to those of a desert, the researchers found. Although the trees are still growing at about 0.25m a year, the team predicts they will not exceed 122-130m. These heights are comparable with historical records of past record-breakers of Douglas fir trees in British Columbia (125m) and mountain ash trees in Australia, inform BBC.

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