(216) Beach Sand Hydrophobicidity Induced as a Result of the Presence of Beach Vitex

Abstract

Beach Vitex (Vitex rotundifolia Lf.) was introduced to coastal Carolina areas in the 1980s. Since its introduction, it has become a major invasive plant problem. Beach Vitex rapidly dominates the vegetation and eliminates many native plant species on primary and secondary coastal dunes. It grows rapidly and reproduces vegetatively by rooting at the nodes. Thousands of fruits, containing one to four seeds each, are produced annually and assist in the plant's spread. Beach sand in areas dominated by Beach Vitex was found to possess hydrophobic qualities, while sand collected from areas not populated by Beach Vitex readily allowed water infiltration. GC-MS analysis of hydrophobic sand extracts showed four peaks that were absent from extracts of non-hydrophobic sand. These peaks were also present in chromatograms of water extracts of Beach Vitex fruits and leaves. Comparison of GC-MS spectra with compounds previously identified in Beach Vitex indicated that one compound was a diterpene (likely ferruginol or abietatrien-3ß-ol). The second compound is likely a flavonoid (possibly casticin, artemetin, or vitexicarpin). Two additional compounds are present at low levels and are possibly phenylnaphthalene compounds. These four compounds appear to be synthesized and incorporated into surface tissues of Beach Vitex leaves and fruits and are transferred to sand during rain events and decomposition. Further studies of Beach Vitex plant parts and beach sands are being conducted to further elucidate the possibility that these chemicals are involved in the intriguing property of sand hydrophobicity. This property may aide Beach Vitex in its competition with plants possessing less expansive root systems.