The Alkali (Scirpus Maritimus L.) and Saltmarsh (S. Robustus Pursh) Bulrushes: A Literature Review
Autecological Classification
Scirpus maritimus and S. robustus are perennial emergent macrophytes that reproduce sexually and vegetatively. Lacking salt glands, succulence, and other adaptations of true halophytes, S. maritimus and probably S. robustus are facultative halophytes that show decreased growth and reproduction in increasingly saline environments yet may persist for centuries in nonsaline habitats (Arnold 1955; Ranwell 1972; Ustin 1984; Kruger and Kirst 1991). These bulrushes are best considered brackish water species that are adapted to flourish at salinities that cause high mortality in freshwater plants yet are able to survive in environments where halophytes dominate.
Investigators often place S. maritimus and S. robustus into categories based on water salinity (Olsen 1950; Van Donselarr et al. 1961; Chabreck 1972; Stewart and Kantrud 1972). However, both species occupy habitats in which salinities fluctuate greatly (Dodd and Coupland 1966a; Palmisano 1970; Pearcy et al. 1982). Both species have mechanisms that allow rapid growth and invasion of bare areas when environmental conditions are favorable and increased survival of reproductive material when conditions are stressful (Palmisano and Newsom 1968; Mercado et al. 1971; Lieffers and Shay 1981; Pearcy and Ustin 1984; Dykyjova 1986; Shay and Shay 1986; Karagatzides and Hutchinson 1991). Scirpus maritimus is one of the few species able to invade established stands of the hybrid Spartina anglica in coastal Europe (Beeftink 1985). In contrast, population sizes of both bulrushes often decrease or disappear in a few years as taller plants flourish after fires or after the cessation of grazing (Beter 1957; Duncan and D'Herbes 1982). Both bulrushes are indicators of disturbance (Beeftink 1966; Palmisano 1970; Pederson and Van der Valk 1984) and rapidly invade bare mudflats (Dahl and Hadac 1941, cited in Chapman 1974; Wilkinson 1970; Flowers 1973; Eilers 1975; Moody 1978; Hutchinson 1982).
Physiologists classify S. maritimus as a C3 plant (i.e., it fixes CO2 directly into a three-carbon molecule), and its net rate of photosynthesis is much below maximal (Rozema et al. 1991). Aerenchymatic tissue develops well in the belowground parts (Tyler 1969). Rhizomes can produce new shoot growth under 2 months of continuous anaerobic incubation and can survive nearly 3 months of anoxia (Barclay and Crawford 1982, 1983; Braendle and Crawford 1987). However, seedlings grown in detritus collected from established stands may show poor growth in anoxic environments (Clevering and Van der Putten 1995). Scirpus maritimus is able to exclude mineral salts while accumulating sugars and other photosynthetic products for osmotic adjustment (Ustin 1984). Reciprocal transplant experiments suggest that this bulrush has little local genetic adaptation and that plants adjust shoot height, mass, density, and flowering frequency to their environment (Karagatzides and Hutchinson 1991).
Devotees of the European Zurich-Montpellier (Z-M) school of phytosociology (Braun-Blanquet 1932) place communities dominated by S. maritimus in a hierarchical system of classes, orders, federations, associations, and subassociations. For example, the federation Bolboschoenion maritimi Dahl & Hadac 1941 occurs in the littoral zones of Czechoslovakian fish ponds (Hejny and Husak 1978) and the association Bolboschoenetum maritimi Van Langendonck 1931 occurs in coastal Norway (Vevle 1985). Scirpus maritimus also occurs as a nodum in the alliance Phragmition in British salt marshes (Adam 1981) and as a companion or differential species in many salt marsh communities in coastal Europe (Westhoff 1979). North American phytosociologists seldom follow the Z-M school. An exception is Looman's (1981) classification of saline areas of the Canadian prairie provinces, where S. maritimus was represented in six of eight associations and was the dominant species in one association.
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