Growth and photosynthetic responses to elevated [C02] in grasses from Tasmanian native pasture

Abstract

Six species of grass (four C3 and two C4) from southeastern Australian native pastures were grown in controlled environment cabinets at current (~370 mol CO2 mol-I) and twice current (~750 mol CO2 mol-I) cabinet [C02]. Photosynthetic gas exchange and above-ground biomass were estimated after seven weeks. Cabinet [C02] had a highly significant impact on above-ground biomass (P<0.0003) with plants exposed to elevated [C02] having on average 78% greater above-ground biomass than the controls. The relative increase of above-ground biomass caused by elevated [C02] varied among species. [C02] during gas exchange measurements and species had highly significant impacts on carbon assimilation and evapotranspiration rates, stomatal conductance and water-use efficiency. Cabinet [C02] had a significant impact on carbon assimilation rate only, for which there was a significant cabinet [C02] x species interaction. Carbon assimilation rate was influenced by cabinet [C02] only for Poa labillardierei, but this may well be related to pot conditions. Three-factor analysis of variance found no interaction between cabinet [C02] and [C02] during photosynthetic measurements, further supporting a lack of photosynthetic acclimation to elevated [C02] in young plants of these temperate Australian grass species.