EFFECTS OF SAND DEPOSITION ON THE INTERACTION BETWEEN AMMOPHILA-ARENARIA, PLANT-PARASITIC NEMATODES, AND PATHOGENIC FUNGI

Ammophila arenaria is a dominant sand-fixing plant species of the Euro pean coastal foredunes. It remains vigorous under regular burial condi tions on seaward slopes, but starts to degenerate when sand accumulati on diminishes. Several hypotheses have been put forward to explain thi s degeneration. In this study, we test the hypothesis that upward grow th of plants following sand burial enables them to escape harmful soil organisms. Plants in a degenerating field stand of A. arenaria and po tted plants grown in sterilized sand (outdoor pot experiment) were bur ied with sterilized or nonsterilized sand. Burial in both sterilized a nd nonsterilized sand resulted in stem elongation, increased numbers o f living shoots, and increased shoot and root biomass. However, when p lants were grown in and buried with sterilized sand, the numbers of sh oots were significantly higher than those buried with nonsterilized sa nd. The new root zone of buried plants was colonized by pathogenic soi l organisms (nematodes and fungi) during the same growing season. It i s concluded that by upward growth through pathogen-free sand, the plan ts benefit, at least temporarily, from escaping its pathogens and para sites.