INHIBITORY EFFECTS OF MYRICA-CERIFERA ON PINUS-TAEDA

Pinus taeda naturally invades Myrica cerifera thickets as the shrub co mmunity succeeds to a maritime forest on southeastern USA barrier isla nds. Potential mechanisms supporting the persistence of M. cerifera th ickets on barrier islands were examined in an environmental chamber. T he inhibitory effects of allelochemicals from M. cerifera leaf litter and the soil in which it grows, and the interaction between allelochem icals and light intensity were quantified for seed germination and see dling growth of P. taeda. Germination of P. taeda seeds was significan tly reduced by treatment with leachate from dead M. cerifera leaves, b ut light level had no significant effect. In contrast, root, shoot and total seedling growth were significantly lower under low light (44 mu mol m(-2) sec(-1)). Root growth under high light (300 mu mol m(-2) se c(-1)) was significantly lower for P. taeda seedlings grown in soil co llected from beneath Myrica thickets. Both root and shoot growth of Il taeda in Myrica soil were significantly higher in the presence of Myr ica leaf litter in high light. Thus, litter accumulation may assist P. taeda in invading Myrica thicket gaps, possibly by counteracting alle lopathic effects of Myrica root exudate. Low light levels and allelopa thic effects may interact and contribute to the persistence of Myrica thickets limiting root growth of invading P. taeda seedlings, thereby reducing competition for space, soil moisture and nutrients.