INERTIA AND RESILIENCE IN THE RESPONSES OF THE AQUATIC BRYOPHYTE FONTINALIS-ANTIPYRETICA HEDW TO THERMAL-STRESS

The physiological responses of the aquatic bryophyte Fontinalis antipy retica Hedw. to high temperatures, ranging from 16 degrees C (control) to 34 degrees C, were investigated experimentally. Plant samples were maintained at the temperature under study for up to 25 days with regu lar determination of physiological variables (pigment ratio and photos ynthetic and respiratory rates). Physiological responses to temperatur e 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 summar y statistics analogous to those used in toxicological research were em ployed to compare responses as revealed by the different physiological variables. In a second series of experiments, the capacity of F. anti pyretica to recover from high-temperature stress was investigated by m aintaining samples at 30 degrees C for 2, 4, or 10 days, then transfer ring the samples to normal conditions (16 degrees C) for 40 days. Phys iological variables were again monitored at regular intervals througho ut both phases of the experiment. In general, good recovery was observ ed even after exposure to high temperatures for 10 days. The results o f these assays allow quantification of the relationship between a pigm ent ratio and net photosynthesis rate.