Summary: Environmental effects on constitutive and inducible
resin defences of Pinus taeda
The ecological literature abounds with studies of environmental effects on plant
antiherbivore defences. While various models have been proposed (e.g. plant stress,
optimal allocation, growth-differentiation balance), each has met with mixed support.
One possible explanation for the mixed results is that constitutive and induced
defences are differentially affected by environmental conditions. In this study,
constitutive oleoresin flow from Pinus tadea was least during periods of rapid tree
growth and most when drought conditions limited growth; this is as expected if
constitutive secondary metabolism is a function of the carbohydrate pool size after
growth has been maximised. Induced increases in resin flow, however, were greatest
in the fastest growing trees during the season of greatest growth. Apparently, resin
production becomes an allocation priority after wounding but not before. Under-
standing environmental effects on plant antiherbivore defences requires physiological
and evolutionary models that account for the differences between constitutive and
induced secondary metabolism.
Pine, Pinus taeda, plant defence, induced defence, bark beetles, Scolytidae,
environmental effects, growth±differentiation balance.