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Sago Pondweed (Potamogeton pectinatus L.):
A Literature Review

Decomposition


Senescence in sago begins shortly after flowering and proceeds as clones flower and die, which exposes clones not in the canopy that, in turn, flower and die (Madsen 1986). In fall, part of the upright stems of sago detach and are washed ashore; remaining senescent stands collapse gradually and decompose on the bottom (Verhoeven 1980a). In some lakes, tons of sago decompose on shore as stems and leaves wash up after being discarded by feeding waterfowl.

Peak sago biomass in a polluted Wisconsin stream occurred after 113 days and senescence began around the end of July (Madsen 1986). After a 129-day growing season, the entire sago community in a North Dakota lake was senescent by 6 October (Kollman and Wali 1976).

Sago decomposes rapidly at old age (158 days in a South African wetland), and the decay products form a rich food for benthic filter-feeding animals (Putschog 1973; Howard-Williams and Davies 1979). Howard-Williams and Davies (1979) showed that nearly all K is lost from decomposing sago within a week but that N and P losses are much slower. Litter bag experiments of Byren and Davies (1986) in another South African wetland showed how important shredding and grazing invertebrates were for increasing surface area for microbial colonization and attack of sago. They estimated complete decomposition in 145 days; listed the animals that dominated the litter bag fauna; graphed the changes in ash, N, and P content of the plant material; and provided micrographs showing changes in microorganisms with time. Indian sago in closed containers decomposed 44% in 60 days (Kulshreshtha and Gopal 1980) and, in large-mesh bags, decomposed completely in 56 days in summer (Purohit 1981).

Decomposition caused by microbes probably is hastened by cuticular damage from periphyton (Howard-Williams et al. 1978). When decaying sago plants react with oxygen, the oxygen depletion and formation of carbon dioxide causes complex chemical changes in the water column and sediments. Calcareous incrustations flake from the leaves, many ions are reduced to more soluble forms, and hydrogen sulfide and several insoluble metallic sulfides are formed (Kollman and Wali 1976).


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