Continuous vegetation cover preventing erosion of coastal sand dunes is essential for the protection and development of productive forestry, farming, and other activities in their vicinity. Use of symbiotic nitrogen fixation to enhance the nutritional status (and thus the vigour) of sand dune vegetation currently depends on the introduction of nursery-raised plants. Local sand and a standard nursery potting compost were seen as possible alternatives for seedling rooting media, but their relative effects on plant performance after transfer to exposed dune sites were unknown. Three nitrogen-fixing species representing a range of tolerance to dune conditions in the north of the North Island (Acacia sophorae (Labill.) C. Martius, Chamaecytisus palmensis (Christ) Bisby et K. Nicholls, and Lotus uliginosus Schk.) were used as the basis for comparison. A slight overall plant size advantage was associated with potting compost during the first year after transplanting, but this was not maintained during the second and third years. Long-term plant survival was not influenced by seedling rooting medium, although mortality of C. palmensis (the least tolerant species) was twice as great in compost-raised plants as in sand-raised plants during the first 6 months. There was no evidence of any consistent effect of seedling rooting medium on relative nitrogenase activity. It was concluded that choice of medium for raising seedlings in the nursery is likely to have only a minor and transitory effect on the performance of nitrogen-fixing plants in sand-dune revegetation projects and species-screening trials.
