DIOECY AND HERBIVORY - THE EFFECT OF GROWTH-RATE ON PLANT DEFENSE IN ACER-NEGUNDO

Male trees had significantly faster growth rates. Leaf defense levels were estimated by measuring leaf characters, such as nitrogen and water content, toughness, tannins and total phenolic compounds. Female and male trees could be distinguished from one another using a discriminant function analysis based solely on leaf characters. Leaves from female trees were tougher than those from males, although no consistent differences were found between the sexes in other leaf characters. When all leaf characters were combined in a multiple regression, females were significantly better defended than males. Males consistently had higher damage rates. Data support the hypothesis that slow plant growth rates select for high defense and suggest that growth rate differences may explain the sexual dimorphism in defenses and herbivory of dioecious plants. -from Authors