Summary
Over the past 50 years the sub-Antarctic has experienced increases in temperature and radiation. Little scientific attention has been paid to the ecophysiological response of vascular plant species growing on these islands and it is unclear what impact climate change may have on these species. This study was undertaken to investigate the photosynthetic efficiency and pigment composition of sub-Antarctic species and their response to temperature using both field measurements and a controlled environment experiment. Five vascular plant species (grasses Poa cookii and Deschampsia antarctica, cushion plant Azorella selago and mega herbs Pringlea antiscorbutica and Acaena magellanica) from sub-Antarctic Heard Island were sampled on five days between December 03 and February 04. Chlorophyll fluorescence (Fv/Fm), leaf temperature and photosynthetic tissue samples (for HPLC pigment analysis) were collected between 10am-2pm for each species. Only the hair grass D. antarctica had low Fv/Fm values coupled with high photoprotective pigment ratios, indicating sustained photoprotection. The grasses displayed characteristics typical of shade adapted species (low chl a/b) while P. antiscorbutica and A. selago showed characteristics typical of sun adapted species (high chl a/b). Deschampsia antarctica and A. magellanica were the species most responsive to naturally occurring changes in temperature and PAR; D. antarctica showing low temperature xanthophyll mediated photoprotection, while 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 and plant growth habit. The response of three sub-Antarctic Poa species (two native and one invasive) to increased growth temperatures (7°C, 12°C and 17°C) were investigated. In all species, Fv/Fm increased and the photoprotective pigment pool decreased with warmer temperatures, suggesting that increases in temperatures may not have a negative impact on these species. Poa foliosa, a sub-Antarctic tussock species, displayed a significantly higher conversion of the xanthophyll pigments to the photoprotective form for all three temperature regimes than either Poa cookii or Poa annua (invasive species). On the basis of Fv/Fm and pigment composition, predicted increases in temperature will not be significantly advantageous for any particular species. This study has found differences in photosynthetic efficiency and pigment composition between sub-Antarctic species in the field and under a controlled environment. Photoprotection and temperature acclimation was occurring and it suggests the studied species will be able to survive predicted climatic changes.