Temperature Related Growth Patterns in Amblystegium riparium

Abstract

Freshly collected Amblystegium riparium (Hedw.) B.S.G. plants were grown submersed at various temperatures ranging from 6 to 330C. Peak growth rates occurred at 230C and death at 330C. Response curves for main axis elongation, lateral branch formation, branch elongation and reproductive branch formation differed in shape, and elongation rates changed over time. Lateral branch growth of branches initiated later was lower than growth of branches initiated earlier in the experiment. High temperature stress resulted in a proliferation of branches. Branch and main axis apices appeared to be the most heat resistant parts of the plants. Amblystegium riparium (Hedw.) B.S.G. (Leptodictyum riparium (Hedw.) Warnst.) is typically found submerged in streams but can grow on wet soils. The type specimen was collected in the Thames River, England, and the species is found widely distrib- uted in the United States (Grout, 1928; Lawton, 1971). Taxonomic relationships of Amblystegium riparium were investigated by Conard (1959). Ecological relationships have received little attention, other than what may be found in floristic studies. An interesting ecological phenomenon in relation to this moss was observed in the Al- exandra Botanic Garden located at Wellesley College, Wellesley, Massachusetts. Am- blystegium riparium grows abundantly in a small artificial stream which extends ca. 400 m within the botanical garden; however the moss is found only in the upper 200 m of the stream. The stream, fed by well water from a stand pipe at the stream origin, was constructed in a naturalistic style with alternating pools, riffles and small (10-20 cm) water falls. The latter habitats, formed by rocks anchored in the cement bottom, are the most common location at which the moss may be found. Since the stream channel is sealed by cement there are no differences in substrate which can explain the lack of the moss in the lower section of the stream. Many sites exist in the lower section which are similar in exposure and current velocity to sites supporting moss growth in the upper section. While biotic factors such as competition can not be excluded as having a role in preventing growth of the moss in the lower section, the distribution patterns of other organisms do not form convincing evidence that such factors are highly important. Since the stream has only one source of water and flows only a short distance, one would suspect that abiotic factors, such as water chemistry, would be relatively con- stant. An analysis of 20 chemical parameters demonstrated little difference in water chemistry. Two factors were discovered which did change significantly along the stream, carbon dioxide concentrations and temperature. This paper represents prelim-