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Scirpus maritimus cultured indoors from mature corms in fertilized soil grows in three phases. During the first 20 days after planting, only shoots grow and the dry weight of plants increases slowly. During the next 100 days, dry matter increases rapidly, the rhizome network expands, shoot numbers peak, and leaf areas reach the maximum size. Single corms can produce as many as 83 shoots, mostly from the rhizomes, in 100 days. Rapid increases in shoot growth precede rapid increases in corm weight. During the next 90 days, the growth rates of shoots, rhizomes, and roots decline, leaves senesce and shoots die, but corm weights increase and ultimately account for most dry matter. Plants can grow as fast as 2.7 cm/day during the first 40 days and reach maximum height in 80 days. Even when crowded, a single corm can produce 4.5 m of corm-bearing rhizomes in 40 days. Plants grown from mature corms planted in outdoor ponds can emerge from 90 cm deep water after 9 weeks of submerged growth.

Density and Yield

Stem or shoot density in healthy stands of Scirpus maritimus and S. robustus is usually about 50-500/m² in S. maritimus; Krisch 1985). During periods of peak biomass, plants seldom shade more than 30-50% of the water or bottom surface.

During dormant periods, nearly 100% of the total live biomass of both bulrushes is below ground. In mature stands, total belowground net production can be as much as three times that of aboveground production, and belowground biomass at times of maximum biomass can be six times aboveground biomass. Peak live standing crop biomass is usually only slightly higher than annual net primary production. Dry aboveground biomass or net annual primary production in healthy stands often exceeds 500 g/m² but seldom exceeds 1,500 g/m² (Table 3). Much greater biomasses are obtained in culture (Dykyjova 1978).

Annual yields of S. robustus achenes sometimes reach 567 g/m² fresh weight, but production in most stands managed for wintering ducks is usually less than 150 g/m². Amounts available for consumption in any given month are usually less than 50 g/m². Achene production in managed stands of S. maritimus is usually less than 100 g/m². A single S. maritimus plant in indoor culture may produce as many as 366 corms and a single corm as many as 28.7 shoots (Mercado et al. 1971).

Distribution of biomass and growth characteristics of S. maritimus strongly relate to habitat. Stands where sediments accumulate or where water depths decrease during the growing season have many leaves and shoots near the water or sediment surface, and plants usually produce copious flowers and fruits. Biomass concentrates in photosynthetic tissue and stems when water depths are low. In contrast, plants growing in erosional biotopes or where water depths increase during the growing season often lose their young leaves. Shoots unable to reach the water surface die. Biomass concentrates in reproductive panicles on the few stems that reach the water surface. In later sections, I address other biotic or abiotic factors that affect or limit biomass.

Chemical and Caloric Content

Water content of the aboveground parts of Scirpus maritimus averages about 79% during the reproductive period. The water content of S. maritimus leaves is about 75% of fresh weight, much less than the 87.5% found in the roots. The moisture content of the achenes averages about 31.1%. On an air-dried basis, the water content of S. maritimus is: stems and leaves 6.6-9.4%, achenes 8.6-12.8%, and corms 13.6%. Air-dried S. robustus achenes contain about 7.7% water.

The ash content of whole S. maritimus plants is about 6.2-14.0% of dry weight. The leaves have the most ash (13.0-15.1%); stems (11.2%), roots (6.0%), corms (4.4-6.4%), and achenes (2.2-5.4%) have less. The achenes of S. robustus have 3.2-6.4% ash.

The maximum gross energy of dry aboveground parts of S. robustus is about 4.5 kcal/g. Energy in S. maritimus is similar (3.8-4.3 kcal/g). Energy in dry S. maritimus corms averages 4.8 kcal/g and in achenes 4.1 kcal/g. Apparent metabolizable energy (AME) of S. maritimus or S. robustus achenes is about 3.2 kcal/g (Miller 1987).

The crude protein in achenes and total aboveground parts of both species likely does not exceed 9.1% of the dry weight. The average protein content is much higher in leaves and stems (10-11% of dry weight) of S. maritimus than in flowering panicles (6-7% of dry weight). In oven-dried (103° C) parts of S. robustus, crude protein is 5.7% in shoots and 5.5% in belowground parts. I found no other information on crude protein content of this species. Popp and Albert (1980) and Cruz and Poe (1975) listed the principal amino acids in both species. Crude fat content in the achenes of both species is about 2.3-4.3% of dry weight. In S. maritimus, crude fat content is greater in the total aboveground parts (2.2-2.4% of dry weight) than in the corms (0.8%). I found no information on the fat content of other parts of S. robustus.

Whole S. maritimus plants contain about 42-47% carbohydrates on a dry-weight basis. Carbohydrates are higher in the flower heads than in the stems or leaves. Carbohydrate reserves in S. robustus corms can attain 86% of dry corm weight. I found no similar information about S. maritimus corms. Carbohydrates in S. maritimus and S. robustus achenes compose about 59% and 67% of dry weight. The principal sugars in S. maritimus rhizomes are known (Barclay and Crawford 1983).

Fiber content in the achenes in S. maritimus is lower (15-25% of dry weight) than in the stems and leaves (21-33% of dry weight). Scirpus robustus achenes are about 14-16% dry weight fiber. Crude fiber content of S. maritimus corms is about 10% of dry weight; no information is available about S. robustus corms. Lignin content of aboveground parts of S. maritimus averages 10.3-11.6% of the dry weight and 12.1-12.8% of the ash-free dry weight.

I list other elements and compounds in various parts of S. maritimus and S. robustus (Table 4). The ability to take up nutrients in nutrient-rich environments is lower by Scirpus maritimus than by representatives of other common emergent genera such as Phragmites, Glyceria, Sparganium, and Typha (Dykyjova 1986). Hothem and Ohlendorf (1989) report selenium concentrations as high as 8.8 g/g of dry weight in S. maritimus achenes from a California reservoir. Little is known about concentrations of other potentially toxic elements in either bulrush species (Outridge and Noller 1991).

In summary, S. robustus (and probably S. maritimus) corms have high carbohydrate concentrations. Achenes are also high in carbohydrates and crude fat. Both bulrushes probably are inelastic in their ability to take up nutrients and are thus probably poor candidates for use in removing nutrients from industrial or domestic effluents.

Decomposition

Decomposition of Scirpus maritimus begins in September in tidal Oregon wetlands; aboveground parts slowly disappear throughout the winter, and by spring only a few withered stems, 7.5-15 cm tall, remain attached to the cormous roots (Eilers 1975). Hall and Yesaki (1988) noted that mortality of S. maritimus peaks in September or October in a British Columbia estuary when dead material increases 6.3 g AFDW (ash-free dry weight)/m²/day. They found that about 85% of the total standing crop enters the detritus pool, and 74% of this dissipates to the estuary and 26% becomes buried in sediments. In Saskatchewan, stems begin dying after September frosts but generally remain standing over winter (Lieffers and Shay 1982a). In the Camargue of France, dead stems of S. maritimus first appear in July and August when early drying probably promotes senescence (Podlejski 1982). Because S. maritimus develops a central woody core by the end of the growing season (Moody 1978) and lacks the buoyancy and larger stem size of some of the other bulrushes, many plants sink and are covered by sediment (Hall and Yesaki 1988). Nevertheless, plant parts washed ashore by tides and decomposed are sometimes an important source of sediment nitrogen for other plants (Beeftink 1966). In small wetlands reclaimed from the sea, where wave action is not severe, S. maritimus detritus accumulates in the centers of circular stands (Clevering and Van der Putten 1995).

Scirpus robustus stems stay erect all winter (Neely 1960). Unlike most other salt marsh emergents in North Carolina, S. robustus plants in experimental decomposition bags lose weight slowly (Waits 1967). Achenes lose only 3% of their original weights after submergence for 30 days (Shearer et al. 1969). A similar experiment by Neely (1956) showed that S. robustus achenes lose only 1% of their original weights after 90 days, a slower rate than that of seeds of 24 other plants eaten by ducks.