Inhibitory Effects of Myrica cerifera on Pinus taeda

Abstract

-Pinus taeda naturally invades Myrica cerifera thickets as the shrub community succeeds to a maritime forest on southeastern USA barrier islands. Potential mechanisms supporting the persistence of M. cerifera thickets on barrier islands were examined in an environmental chamber. The inhibitory effects of allelochemicals from M. cerifera leaf litter and the soil in which it grows, and the interaction between allelochemicals and light intensity were quantified for seed germination and seedling growth of P taeda. Germination of P taeda seeds was significantly reduced by treatment with leachate from dead M. cerifera leaves, but light level had no significant effect. In contrast, root, shoot and total seedling growth were significantly lower under low light (44 Rmol m-2 sec-1). Root growth under high light (300 Rmol m-2 sec-1) was significantly lower for P taeda seedlings grown in soil collected from beneath Myrica thickets. Both root and shoot growth of P taeda in Myrica soil were significantly higher in the presence of Myrica leaf litter in high light. Thus, litter accumulation may assist P taeda in invading Myrica thicket gaps, possibly by counteracting allelopathic effects of Myrica root exudate. Low light levels and allelopathic 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.