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Characteristics of Three Populations of a Swamp Annual Under Different Temperature Regimes

Christy, E. Jennifer, Sharitz, Rebecca R.
Ecology 1980 v.61 no.3 pp. 454-460
Ludwigia, ecotypes, evolution, germination, growing season, herbaceous plants, reproductive performance, seedlings, streams, survival rate, swamps, water temperature, Savannah River, South Carolina
This study was undertaken to examine rapid evolution in an herbaceous plant species in response to strong selection associated with increases in temperature. Differences in growth and reproduction in three populations of Ludwigia leptocarpa (Nutt.) Hara, an herbaceous plant dominant along the edges of streams receiving heated nuclear reactor effluent on the United States Department of Energy's Savannah River Plant (SRP) in South Carolina, USA, were examined for two growing seasons. Two populations of this semi—aquatic herb were in areas with elevated water temperatures, and one population was in an undisturbed swamp. In each of the populations in warmer water, growth and reproductive output were significantly higher than in plants from the undisturbed site. Total percentage germination under controlled temperatures from 22° to 42°C did not differ among the three populations; however, initiation of germination was delayed in all three at 22°. Seedlings from all three populations showed similar growth responses at 22°, whereas at 32° seedlings from the higher temperature locations grew more rapidly. At 42°C, survivorship of seedlings from all three seed populations was low. These results indicate selection for temperature—tolerant ecotypes in the disturbed areas.