A detailed study of how the environmental factors temperature, light, water content and carbon dioxide concentration affected photosynthesis of the two common mosses Bryum argenteum and B. pseudotriquetrum was conducted at Cape Hallett. Four microclimate recording stations were set up to monitor conditions at selected key plant sites. Complete matrices for Bryum argenteum and B. pseudotriquetrum ... were constructed relating photosynthetic performance to light level (0-0.75 full sunlight), temperature (-10 to +30°C), CO2 concentrations (0-2500 ppm, ambient is 350ppm) and water content (saturation to dryness). Diel courses were recorded for both moss species at ambient and elevated CO2 levels. CO2 levels were measured in air samples taken from amongst the moss plants. The physiological versatility of B. argenteum was investigated by heavily shading some samples for two weeks then removing the cover from half of the shaded area and watching the consequences. An automatic chlorophyll fluorescence site was set up to monitor the activity of the lichen Physcia caesia.