Effects of Light Intensity and Temperature on Photosynthesis and Respiration of Two East Antarctic Mosses, Bryum argenteum and Bryum antarcticum

Abstract

Gametophytes from Victoria Land were tested in the laboratory at McMurdo Station, Antarctica. Net photosynthetic and respiratory rates were determined by measuring oxygen exchange in air containing 1% CO, (v/v) with respirometers. Optimal temperatures for net photosynthesis were 25-300C and 15-200C with maximal rates of 117 and 27-37 pliters 02 evolved hr-1 cm-2 for Bryum argenteum and B. antarcticum, respectively, whereas the respiratory rates increased with increasing temperatures throughout the temperature ranges tested. In both species, light compensation points were ca. 1.6 mW cm-2 and light saturation points were reached at 8-10 mW cm-2 when determined at 150C, but shifted to about one half these values when determined at 50C. However, higher rates of net photosynthesis were obtained at 50C and light intensities less than 4 mW cm-2 for B. argenteum and less than 3 mW cm-2 for B. antarcticum as compared to rates measured at 150C and low light in- tensities. Field observations indicated that direct sunlight adversely affects chlorophyll contents of B. antarcticum, but under conditions of low light intensi- ties, a dark period, and nutrient supply an increase in chlorophyll content was obtained in samples collected from the field. Apparently, these mosses do not require low temperatures or high light intensities to survive the harsh antarctic environment, but have a capacity to endure these conditions.