Microbial communities in southern Victoria Land streams (Antarctica) I. Photosynthesis

Abstract

The glacier-fed ephemeral streams of southern Victoria Land (ca. 78° S, 164° E) are colonised by an epilithon dominated by cyanobacterial mats and films. Biomass levels are often high (> 15 μg Chl a· cm ⁻²). The mat structure, pigment and photosynthetic characteristics of these communities have been investigated on site. The mats in high light environments have a layered structure with high levels of light shielding accessory pigments in the upper layers and elevated chlorophyll a and phycocyanin concentrations in the lower layers. Photosynthetic rates per unit area (0.4–3.5 μg C· cm ⁻² · hr ⁻¹) fall within the range reported for temperate communities. P vs. I curves were used to separate high, intermediate and low light communities. I_k values for high light communities were at or lower than PAR recorded at midnight in the polar midsummer (ca. 100 μE m ⁻² · S ⁻¹). We did not detect photoinhibitory responses at the midday light intensities. In situ continuous nutrient enrichment experiments failed to demonstrate N or P limitation to pigment content or photosynthetic rates. We suggest that the growth of these communities is controlled by factors other than light and nutrients.