PHOTOSYNTHESIS AND RESPIRATION IN THE SUB‐ANTARCTIC TUSSOCK GRASS POA COOKII

Abstract

SUMMARY Poa cookii dominates the tussock grasslands at islands of the Kerguelen Province of the sub‐Antarctic. In common with other sub‐Antarctic Poa species it is highly productive. Infra‐red gas analysis studies at Marion Island (46° S, 37° E) showed that P. cookii is a C3 photosynthetic type plant, possessing a high CO2 compensation concentration (c. 100 p.p.m.) and apparently high rates of photorespiration. However, photosynthetic light saturation was not attained at a photosynthetic photon flux density (PPFD) of 2000μmol m−2s−1, possibly due to leaf anatomical features causing shading of the chlorophyllous mesophyll. Compensating irradiance values were 5 to 11 μmol m−2s−1. Net photosynthesis occurred below 0 °C and increased with temperature up to 10 to 12 °C, remaining constant up to 19 to 23 °C, depending in PPFD. Dark respiration increased exponentially with temperature and at 32 °C the temperature optimum had not been reached. Photorespiration also increased with temperature but rates were lower than those of dark respiration. Increasing the wind velocity over a leaf immediately decreased the net assimilation rate, which then slowly recovered to almost the original level. It appears that the grass is well‐adapted to sub‐Antarctic conditions of low light, low (seldom freezing) temperatures and high wind.