FERTILIZATION MITIGATES CHEMICAL INDUCTION AND HERBIVORE RESPONSES WITHIN DAMAGED OAK TREES

Previous work has shown that fertilization can mitigate across-year in duced resistance among individual Alaska paper birch, supporting the h ypothesis that induction results from nutrient deficiency rather than active defense. The present study suggests that fertilization can prev ent induction responses in oak within one season, and among leaves wit hin individual trees. Saplings of two oak species, divided among ferti lizer treatments within a plantation, were defoliated to varying degre es by a gypsy moth outbreak during spring. We monitored foliage chemis try and insect herbivore distributions during summer and fall of the s ame year. Damaged leaves within unfertilized Quercus prinus saplings s howed increases in foliar astringency and proanthocyanidins. Within fe rtilized trees, damage did not induce increases in either astringency or proanthocyanidins. Defoliation also induced increases in proanthocy anidins and astringency within Q. rubra saplings, but induction was un affected by fertilization. On both tree species, the distributions of certain insect guilds were skewed away from damaged leaves on unfertil ized trees, but independent of damage on fertilized trees. We suggest that the effects of fertilization on induction can vary among tree spe cies, and can occur at more than one spatial and temporal scale. Our d ata support the view that nutrient availability may affect phytochemic al induction and herbivore responses.