Sago Pondweed (Potamogeton pectinatus L.):
A Literature Review
Propagation and Management
Plant physiologists often select sago for experimental purposes because the plant can be grown in pure liquid media, which eliminates variables introduced by soils or other substrates. Sago is easily cultured from drupelets, turions, rhizomes, leafy tops, or cuttings in vessels either indoors or outdoors (Sauvageau 1894, cited in Muenscher 1936a; Moore 1915; Bourn 1932; Otto and Enger 1960; Teeter 1963; Yeo 1965; Huebert and Gorham 1983; Van Wijk et al.1988). Vessels made of stoneware, wood, plastic, fiberglass, or glass are suitable. Either natural or artificially compounded liquid media and bottom substrates have given good results, as have tap water and garden soil. Water depth, illumination, circulation, and other environmental factors are varied according to the purposes of the experiment, but for best growth, temperatures are usually maintained at 20-22° C.
Moore (1915) and Muenscher (1936a,b) discussed storage and germination of sago drupelets and reviewed the early work of Sauvageau (1894), Crocker (1907), and Fischer (1907) on germination techniques. Drupelets can be stored either wet or dry, but wet storage in natural waters at temperatures just above freezing approximates the dormancy period for materials from temperate regions. McAtee (1911) urged that drupelets be planted immediately after harvest or removal from cold storage. Van Wijk (1983) observed best (40%) germination to occur when drupelets were dried for 3 months in sediment, ripened 14 months in room-temperature tap water, and placed in fresh water.
Turions can also be stored in water at low temperatures or packed in layers of saturated moss. Dry storage in straw at low temperatures is also recommended if turions are free of bottom soil. Turions can also be dipped in paraffin and stored for up to 4 years (Yeo 1965). Van Wijk (1983) found uniformly high (100%) germination indoors of turions produced in outdoor culture if the turions were allowed to remain in sediments through winter (stratification) and then were subjected to temperatures between 15° C and 25° C.
Many attempts have been made to establish large sago stands for wildlife (McAtee 1917, 1939; Terrell 1923; Bourn 1932; Martin and Uhler 1939; Sharp 1939; Steenis 1939; Donnelly 1968). Drupelets can be directly harvested or sometimes readily collected along lake shorelines after late summer storms. Even drupelets exposed on dry shorelines for more than 1 year in northern climates have given good germination in as little as 4-10 days. Drupelets can be broadcast in shallow water, but best results have been obtained with spring plantings of drupelets, turions, or plant tops imbedded in clay and dropped from boats. Recommended water depths are usually < 2 m. Turions or rhizomes can also be successfully planted in depressions cut with a metal pipe and then covered with a few centimeters of the parent substrate. Berge (1987) achieved best stands by planting single turions attached to nails with rubber bands or several turions in polyethylene produce bags weighted down with gravel; poorer stands resulted from plantings of turions contained in peat pots or with the older method where turions were imbedded in clay. All plantings were done inside snowfence enclosures (58 m2) in naturally protected, open water areas.
Planting density of 3,000 plant parts per hectare is recommended. Delicate growth occurs the first season if sago drupelets are sown, but thick stands normally develop by the second season when root systems have become established.
It is not reasonable to expect great amounts of sago production from plantings made among potential competitors such as Myriophyllum, Ceratophyllum, Ruppia, and Chara, or in turbid or acidic waters or lakes of large fetch where wave action is severe. Best success can be expected in Cl- or SO4-dominated waters with salinities 5-15 g/L. Davison and Neely (1959) stated that sago required waters with > 50 mg/L alkalinity for successful propagation.
Waterfowl managers often attempt to increase sago through water level manipulations, but the results have been unpredictable. In a Michigan wetland, sago, in one season, replaced stands of Polygonum lapathifolium and Echinochloa spp. that had occupied dewatered areas the previous year; the sago germinated and grew in water < 25 cm deep (Lutz 1960). Partial dewaterings in a Minnesota wetland resulted in a marked increase in sago growth and drupelet production and a decrease in less-desirable submersed macrophytes (Harris and Marshall 1963). Sago populations recovered well in an Iowa wetland dewatered for an entire growing season (Van der Valk and Davis 1978). In a eutrophic Ohio impoundment, sago did not increase greatly, but populations shifted to shallower waters after a partial winter drawdown, likely because of severe competition by the earlier-sprouting Najas, especially at deeper sites (Gorman 1979).
Long-term experiments in Utah to create openings in Typha stands to increase use by waterfowl have employed various combinations of dewatering, mowing, crushing, burning, applying herbicides, and blasting with explosives (Nelson and Dietz 1966). Sago and other desirable waterfowl food plants replaced Typha on some plots, but others were invaded by the less desirable Tamarisk.
Waterfowl managers have had little success in restoring sago to former levels of abundance in waters populated with rough fish and high in calcium carbonate. In a Michigan wetland with a marl bottom, wind-caused turbidity early in the season lessened as sago growth developed, but was replaced by carp-caused turbidity during the middle of the growing season (Rich 1966). Ongoing experiments of Butler and Hanson (1985, 1986, 1988, unpublished) in a Minnesota wetland indicate that direct precipitation of calcium carbonate can add to wind- and fish-generated resuspension of calcium carbonate, silt, clay, and organic material and result in eliminating submersed macrophytes.
Sago increased dramatically in a Wisconsin wetland after two consecutive summer dewaterings that greatly reduced carp densities and likely released nutrients from highly organic bottom sediments (Linde 1965). Partial dewatering, followed by chemical treatments, contract fishing, the installation of an electric fish barrier to prevent spring spawning of carp, and the construction of breakwaters to create sheltered areas were done before a successful sago planting in a Wisconsin wetland (Berge 1987). Increases in sago also were sometimes noted when slightly brackish (2 g/L) wetlands in the prairie or aspen parkland region of Canada were subjected to partial or total dewaterings (Brent Wark, Ducks Unlimited Canada, personal communication). Many of these wetlands had not been dewatered for 20 years. The dewaterings were done to create inter spersions of emergent plants and open water attractive to breeding waterfowl, rather than to increase submersed macrophytes. Nevertheless, partial draw downs (e.g., water levels in a 1.2-m-deep wetland reduced to 0.3 m by August) usually resulted in an increase in all pondweeds, including sago. Results were more variable with complete drawdowns, where wetlands were kept dry most of the spring and summer and supplied with shallow water in early August, but in some instances, sago abundance was greatly increased over pre-drawdown conditions.
Natural recolonization of sago and other submersed macrophytes in areas where they have been absent for decades can occur with improvements in water quality, even in areas where it is unlikely that propagules are present. For instance, in the tidal Potomac River, it was suspected that sago propagules were washed into the river from tributaries during spring runoff (Carter and Rybicki 1986).
Site preparation, harvesting techniques for propagules, propagule treatment and storage, and water management techniques for sago and other hydrophytes have been reviewed by Kadlec and Wentz (1974).
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