Developmental and induced responses of nickel-based and organic defences of the nickel-hyperaccumulating shrub, Psychotria douarrei

Developmental and inducible changes in metal-based (nickel (Ni)) and organi c defences (phenolics) are compared in the Ni-hyperaccumulating shrub, Psyc hotria douarrei. Young and old leaves of P. douarrei shrubs, subjected to different degrees of simulated herbivory, were analyzed for metals, tannins, macronutrients a nd total carbon, and compared with a co-occuring nonhyperaccumulator shrub, Ficus webbiana. Leaf age affected both nickel Ni-based and organic defences in P. douarrei; foliar metal concentrations were higher in mature leaves, whereas organic defences were higher in young leaves. Neither metal-based nor organic defen ces were increased by simulated herbivore damage, implying noninducibility, although some organic defence compounds were significantly reduced. P. dou arrei had a greater percentage of total phenolics, condensed tannins and pr otein precipitation ability than F. webbianai. Since total carbon content d id not differ between species, Psychotria invests more of its leaf carbon b udget in organic defences than does Ficus. Data suggest that P. douarrei foliage is well protected by Ni, but tannins have multiple functions. The high concentrations of tannins in Psychotria l eaves might function as a detoxification mechanism for elevated cytoplasmic metal concentrations, in addition to providing defensive benefits.