Seasonal content of tntal soluble carbohydrate, total soluble protein, free fatty acids and alkaloids were examined in A population of Ceratophyllum demersum growing in a pond on the 8011thwestern edge of the Canadian Shield. Total soluble carbohydrate and total soluble protein were inversely correlated. Free fatty acids were dominated by (16:O k16:1), 18:2 and 18:3. Relative proportions of the different free fatty acids remained roughly constant throughout the season. Alkaloid concentrations showed large fhictuetions, with the highest values found during the first half of the season. Carbohydrate and protein contents of associated periphyton were not correlated with host macrophyte metabolism.
1. Introduct,ion
CerutvphyllurrL demersum I,. is a very coninion rriacrophyte in central North America, where it occupies a wide range of habitats . It lacks roots and is often anchored to the bottom by older portions of stern buried in sediment. This niacrophyte can grow at a variety of depths, ranging from just below the surface to 14 m (PIP and SIMMONS, 1986).
Despite the great contribution which C. demersum makes to the priniary production of many aquatic ecosystems (e.g. BEST, 1976, 1979; PIP and SUTHERLAND-GUY, 1987), little information is available regarding the chemical coniposition of this species over the course of a growing season, particularly wit,h regard to free fatty acids. The objective of the present study was to examine the seasonal flux of total soluble carbohydrate, soluble protein, free fatty acids and alkaloids in a conmiunity of G. denzersum in a pond located in southeastern Manitoba, Canada. Soluble carbohydrate and protein contents of the periphyton found on the plants were also examined for conlparison.
2. The Study Site
The study was conducted during May to August, 1982 in an undisturbed pond approxiinately 2 ha in area located 18.2 kin west of Rennie, Manitoba on Highway No. 44 (49"54'40"N, 95'47'17" W). The bottom of the pond, with a maximuni spring water depth of 3 111, consisted of a layer of peat and sunken logs overlying a clay base. Subinerged niacrophytes covered niost of the bottom and consisted of