COMPETITIVE AND MUTUALISTIC INTERACTIONS BETWEEN PITCH PINE, BAYBERRY, AND THEIR SYMBIONTS

We investigated the competitive and mutualistic interactions between c ommon colonizers of low productivity sites in southern New Jersey's Pi nelands National Reserve. These included pitch pine (Pinus rigida), th e N-2-fixing bayberry (Myrica pensylvanica), and their respective symb ionts Pisolithus tinctorius and the actinomycete Frankia. We initiated a a-year greenhouse study to examine the effects of intra- and inters pecific plantings of these woody perennials, with and without the endo bionts P. tinctorius and Frankia. Biomass accumulation and partitionin g, leaf nutrient concentrations, and a N-15-dilution technique were us ed to evaluate the success of the different planting combinations. Aft er two growing seasons, symbionts increased the development of their h osts. Pines in interspecific plantings with bayberry exhibited similar levels of total production to those grown with conspecifics, whereas biomass partitioning to the shoots was increased in the mixed-species plantings. Bayberry exhibited trends toward higher production when Fra nkia rapidly colonized its roots or when the associated pine lacked P. tinctorius. There was no evidence that nitrogen fixed by bayberry see dlings reached companion pines after 2 years. Timing of endobiont colo nization was a dominant factor influencing plant growth and the capaci ty to mitigate competition for Limiting resources.