Summary
Two vascular plant species (hair grass Deschampsia antarctica and herb Acaena magellanica) from sub-Antarctic Heard Island were sampled on 5 days between December 2003 and February 2004. Chlorophyll fluorescence and leaf temperature were determined in the field over midday and photosynthetic tissue samples collected for subsequent analysis of photosynthetic and UV-B screening pigments. D. antarctica had low Fv/Fm values coupled with high photoprotective pigment ratios, indicating sustained photoprotection during the study period while A. magellanica showed little sign of photoprotection. Acaena magellanica contained more than 3 times the amount of UV-B screening pigments than D. antarctica. Photoprotective pigment content in both species was responsive to naturally occurring changes in temperature and PAR with D. antarctica showing low temperature xanthophyll-mediated photoprotection, whilst A. magellanica indicated potential for protection at higher temperatures. Trends in pigments levels and response to temperature and PAR are discussed in relation to photosynthetic acclimation, plant growth habit and survival under a changing climate.