Dispersal vectors of Myrica-infective Frankia in a coastal barrier ecosystem

Low nitrogen availability is a significant limitation to the local flora in sandy, nutrient-poor soils of barrier islands.  Symbiotic nitrogen fixation confers a significant advantage to host plants in these soils.  On the Virginia barrier islands, thickets dominated by the actinorhizal shrub, Myrica cerifera, represent the first woody seral stage of succession.  Myrica establishment in recently accreted soils depends upon the presence of the actinomycete, Frankia.  Previous research has established that infective and effective Frankia may exist in soils devoid of the host plant, although means of dispersal have not been determined.  We hypothesize that passerine birds may disperse the actinomycete.  Our field observations and bioassays with sterile Myrica seedlings indicate that infective propagules of Frankia may be dispersed to uncolonized sites via avian defecation.  Seedlings developed nodules after inoculation with a dilute solution of bird feces.  In addition, we have preliminary evidence that the actinomycete may be present on or in the fruits of Myrica.  If so, the role of birds in dispersal and expansion of shrub thickets is greater than previously thought.