Above and belowground community development in a marine sand dune ecosystem

Transects across undisturbed marine sand dunes sequentially traversed the following plant communities: littoral, foredunes, intradune complex of ridges and hollows, deflation plain, myrtle forest, and mature conifer forest. Organic carbon levels were low in the littoral zone and increased across the dune ecosystem landward to the forest communities. The highest percentage of nutrients was isolated from the heavy fraction of soil residues. Soil microfloral populations responded to vegetation, physical dune characteristics, and seasonal moisture patterns. Populations of bacteria and actinomycetes were higher in winter than during summer sampling periods in all communities. Populations of microscopic fungi were higher in winter in all the communities except the hollows. The distribution of vesicular-arbuscular mycorrhizal fungi responded to vegetation and sand dune succession but did not display seasonality. Species of Gigaspora and Acaulospora were the most commonly isolated VAM fungi.Sand aggregation increased along the dune transect and was correlated to plant community succession: the most highly aggregated soil was found in the two forest communities. With scanning electron microscopy, sand grains and organic residues were observed entangled by strands of filamentous mciroorganisms. Many of the filaments were of the dimensions of VAM fungi, which may be important for the release of nutrients associated with the cementing agents of sand aggregates and for the survival of early pioneer plants of sand dunes.