BIOLOGY OF THE SALINITY TOLERANT GENUS RUPPIA L IN SALINE LAKES IN SOUTH-AUSTRALIA .2. POPULATION ECOLOGY AND REPRODUCTIVE-BIOLOGY

A study of the genus Ruppia in south Australia was performed. Two of the species of Ruppia found in south Australia, R. polycarpa Mason and R. tuberosa Davis and Tomlinson, are found primarily in temporary salt lakes and exhibit annual life cycles. A 3rd species, R. megacarpa Mason is perennial and is found only in permanent waters. The differences in the life cycles and reproductive biology of these species were considered. The standing crop of the annual species was always considerably less than that of the perennial; in Little Dip Lake R. megacarpa communities had 410 g m-2 DW [dry weight] of total plant matter (282 g m-2 DW of R. megarcarpa) in Nov. 1977 whereas the annual population of the R. tuberosa community had a standing crop of 11.7 g m-2 DW (3.3 g m-2 DW of R. tuberosa). Although these values varied with season and the salinity, depth and permanence of habitats, the difference between annuals and perennials held. Standing crop and time of seasonal maximum and minimum values showed further differences between annual and perennial life cycles; in Little Dip Lake, ranges were 103 (Sept.)-383 (Nov.) g m-2 DW for R. megacarpa and 1.6 (June)-99.0 (Sept.) g m-2 DW for R. tuberosa. R. polycarpa ranged from 4.2 (June) to 60.0 (Sept.) g m-2 DW in a comparable habitat, Blue-Green Algal Pool. Partitioning of Ruppia into plant parts reveals differences between annual and perennial forms as well as seasonal differences within each life cycle. In the perennial, reproductive parts (flower sand seeds) always comprise only a small part of the total dry weight, whereas in the 2 annual species the proportion of reproductive parts (flowers, seeds and turions) is higher in all seasons. Even when vegetative growth of annuals is at its maximum, the percentage of dry weight accounted for by reproductive parts is higher than at any stage in the life cycle of the perennial. Both seeds and asexual turions play a major role in propagating the annual species. The perennial spreads mainly by rhizomes. Turions are produced by R. polycarpa and R. tuberosa in Australia. Two structural types of turions were present on R. tuberosa and only 1 of these on R. polycarpa. The anatomy and role of these organs in propagation are considered.