Ecophysiological adaptations of coastal halophytes from foredunes and salt marshes

Abstract

Ecophysiological strategies of coastal halophytes from foredunes and salt marshes are discussed. A comparison is made of the factors that limit growth in salt marshes and sand dunes. In salt marshes, zonation and succession are primarily governed by variation in soil salinity, which strongly depends on inundation with seawater. Results are described of experiments which aim at separating salinity and inundation effects on growth, osmotic and mineral relations in a comparison of salt-marsh halophytes. The growth response of plants cannot simply be correlated (and causally explained) with the concentration of Na, C1, and K in the tissues. Also, the compatible osmotic solutes proline and methylated quaternary ammonium compounds may accumulate both in species with a positive response to increased salinity and in species with a growth reduction under seawater inundation. More likely inadequate adaptation of the plants water potential with these components is partly the cause of retarded growth. Disfunctioning of the plant in this respect may be at three levels: (a) total water potential of the plant, (b) (loss) of turgor pressure potential; (c) regulation at the cellular level.The ecological importance of some factors in seawater other than sodium chloride is considered. In coastal sand dunes airborne rather than soil salinity limits plant growth, together with the effects of abrasion, sand accretion, drought and the poor nutrient status of the dune sand. Adaptations of sand-dune species to these factors may consist of: large seeds with storage tissue germinating in the dark and seedling growth enough to emerge through the accreted sand. Aerial parts must be resistant to mechanical damage (high wind speed and abrasion), possibly by a sclerophyllous and tough structure. Efficient nutrient uptake, translocation and retranslocation seem to help survive sand-dune species in a nutrient-poor rooting medium. Outline and scopeThis paper aims at a discussion of abiotic factors influencing salt-marsh halophytes and species from the foredunes, which are more or less under the direct influence by the sea, either by seawater inundation (salt marshes) or seawater spray together with sand drifting at high wind speeds. Watkinson

Salt Spray Induces Osmotic Adjustment and Tissue Rigidity in Smooth Cordgrass, Spartina alterniflora (Loisel.)

“…Plants that inhabit areas where contact with salt is unavoidable, either through saline surface waters or sea spray, tend to be more tolerant to salt. While studies on dune plants have reported elevated leaf necrosis, reduced growth, and diminished reproductive capacities attributed to salt spray, the extent of injuries and the rates of mortality are substantially lower than inland plant species (Rozema et al 1985;Sykes and Wilson 1988;Cheplick and Demetri 1999). Our results are in contrast with studies that have shown decreased growth in S. alterniflora with elevated surface-and soil-water salinities (Mooring et al 1971;Longstreth and Strain 1977;Vasquez et al 2006).…”

“…After 4 weeks of treatment, both Ψ leaf and Ψ xylem decreased due to foliar applications of salt. Lowering of Ψ is frequently observed in coastal plants when challenged by high salinities (Longstreth and Strain 1977;Rozema et al 1985;Hester et al 2001) and are often attributed to accumulations of vacuolar ions and/or the production of cytosolic organic compounds (compatible solutes ;Zhu 2001;Flowers and Colmer 2008). Although S. alterniflora can maintain some control over ion uptake from seawater, perhaps including selective uptake of K + over Na + , buildup of Na + does occur in shoot tissues (Smart and Barko 1980;Bradley and Morris 1991;Vasquez Fig.…”

“…species (Rozema et al 1985). One such species, Spartina alterniflora Loisel., dominates coastal marshes of Eastern and Gulf Coasts of the United States and is capable of tolerating the characteristically high saline conditions of regularly flooded tidal salt marshes.…”

“…In one study, for example, appreciable salt deposition was measured as far as 2 km from the shoreline (Rozema et al 1983). Therefore, despite their distances from the water's edge, upper marsh plants may be susceptible to considerable abiotic challenges from salt (Ahmad and Wainwright 1976;Rozema et al 1985). Furthermore, salt spray can be an important abiotic factor that strongly influences plant survival and species composition (e.g., Oosyting and Billings 1942;Barbour 1978;Griffiths and Orians 2003).…”

“…Furthermore, salt spray can be an important abiotic factor that strongly influences plant survival and species composition (e.g., Oosyting and Billings 1942;Barbour 1978;Griffiths and Orians 2003). Indeed, the ability of a plant to tolerate salt spray is a contributory factor to zonation and succession in many coastal plant ecosystems (Rozema et al 1985;Wilson and Sykes 1999;Griffiths and Orians 2003;Griffiths 2006).…”