Impact of saltwater spray andsand deposition on the coastal annualTriplasis purpurea (Poaceae)

Abstract

Pioneer coastal plants occur in areas where sand movement and airborne salt are common. The objectives of this study were to (1) quantify natural levels of salt and sand deposition in relation to distance from the shoreline of Staten Island, New York, and (2) experimentally determine the impact of saltwater sprays and partial sand burial on growth and reproduction of the native dunegrass Triplasis purpurea. This summer annual matures most seeds in cleistogamous spikelets on leaf sheath-enclosed axillary panicles along culm internodes. Levels of salt deposition onto T. purpurea shoots over 6 d were determined with a conductivity meter to be 175 μg/cm(2) at 39 m from shore in 1997, but declined rapidly with increasing distances to 90 m. Sand deposition over 1 mo in the summer averaged 30 mm at 72-90 m from shore. In a greenhouse factorial experiment, seedlings were unburied, buried to 50% height, or buried to 75% height and simultaneously subjected to no sprays, two sprays/wk, or six sprays/wk of seawater over the summer. Sand deposition increased plant size and seed production, but seawater sprays were mostly detrimental, reducing plant size, seed production, and seed mass. However, T. purpurea tolerated moderate levels of salt deposition. The stimulation of growth and reproduction in partially buried plants is adaptive on the sandy soils. Prolific seed production and tolerance to moderate levels of airborne salt allow this annual to maintain high population densities close to shore.