Inertia and Resilience in the Responses of the Aquatic Bryophyte Fontinalis antipyretica Hedw. to Thermal Stress

Abstract.

The physiological responses of the aquatic bryophyte Fontinalis antipyretica Hedw. to high temperatures, ranging from 16°C (control) to 34°C, were investigated experimentally. Plant samples were maintained at the temperature under study for up to 25 days with regular determination of physiological variables (pigment ratio and photosynthetic and respiratory rates). Physiological responses to temperature did not differ significantly between mosses collected from a normal river site and from a river site with abnormally high temperature due to input from a hot spring. Simple curve-fitting procedures and summary statistics analogous to those used in toxicological research were employed to compare responses as revealed by the different physiological variables. In a second series of experiments, the capacity of F. antipyretica to recover from high-temperature stress was investigated by maintaining samples at 30°C for 2, 4, or 10 days, then transferring the samples to normal conditions (16°C) for 40 days. Physiological variables were again monitored at regular intervals throughout both phases of the experiment. In general, good recovery was observed even after exposure to high temperatures for 10 days. The results of these assays allow quantification of the relationship between a pigment ratio and net photosynthesis rate.