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Defenses of young leaves - Drs. Coley and Kursar  Although
leaves may be young and expanding for only a few weeks of their life, 70% of
a leaf's lifetime damage occurs during this short period. Despite strong selection
for defense, our studies in Africa, SE Asia and Panama show that any given species
only invests in a subset of the possible defenses. One 'strategy' is to invest
in effective chemical defenses during the period of expansion before the leaf
can toughen up. Another 'strategy' is to expand rapidly, doubling in size every
day, thereby shortening the window of vulnerability. However, rapid expansion
requires high nitrogen and low toughness, and because of energetic constraints,
the synthesis of secondary metabolites and photosynthetic machinery must be
delayed until the leaf stops expanding. A major thrust of our present research
is to characterize the secondary chemistry of fast- and slow-expanders, as we
expect they will have very different chemical attributes. Similarly, the herbivores
that specialize on fast- and slow- expanders are subject to different rates
of predation and may have different opportunities for sequestering plant compounds
to use in their own defense. |
Copyright University of Utah 2005