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 ha s met with mixed support. One possible explanation for the mixed results is that constitutive and induced defences are differentially affected by envi ronmental 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 me tabolism is a function of the carbohydrate pool size after growth has been maximised. Induced increases in resin flow, however, were greatest in the f astest growing trees during the season of greatest growth. Apparently, resi n production becomes an allocation priority after wounding but not before. Understanding environmental effects on plant antiherbivore defences require s physiological and evolutionary models that account for the differences be tween constitutive and induced secondary metabolism.