How tall can a tree grow? Does sunlight or water limit the size and photosynthetic capacity of a leaf? Could constraints on leaf growth really determine the height of a tree? These are all questions that Alana Oldham of Humboldt State University, CA, was eager to answer as she and her colleagues dangled from an ancient redwood tree well over a football field's length in height above the ground.
Most trees, and many other plants, have thicker leaves on the top of their canopies with wider, more expanded leaves below. This difference in "sun" vs "shade" leaves is usually explained as an adaptation to different levels of light availability within the plants' crown. However, Oldham and her collaborators set out to investigate whether water stress might play an equal or more important role than light availability on the variation in top to bottom leaf anatomy in one of the tallest plants on earth, the redwood tree (Sequoia sempervirens). They published their novel findings in the July issue of the American Journal of Botany (http://www.amjbot.org/cgi/reprint/ajb.0900214v1).
In order to separate the effects of light from water potential the authors collected data on a range of morphological and anatomical variables in leaves using a paired design, sampling from the inner and outer crown of each of five redwood trees at increasing height positions.
"This is the first time plant anatomists have collected height-paired leaf samples from both the inner and outer crowns of trees of significant height," Oldham notes. "Accessing the outermost branch tips in trees of this size requires risky techniques that have taken many years for more experienced canopy researchers than I to learn and develop. Only by obtaining leaves that grew at the same height in the tree but in different light environments could we separate the effects of light availability from those of h
|Contact: Richard Hund|
American Journal of Botany