Productivity of Trifolium subterraneum and Phalaris aquatica under warmer,high CO2 conditions

Despite the importance of grass-legume pastoral ecosystems worldwide, there is little known about the impacts of concurrent increase in temperature an d atmospheric CO2 concentration on their productivity. Pure and mixed swards of subterranean clover (Trifolium subterraneum) and p halaris (Phalaris aquatica) were established under ambient and warmed (+3.4 degreesC) air temperatures, at ambient and 690 mu mol mol(-1) CO2 concentr ations in field tunnels in temperate south-eastern Australia. Over one year, elevated CO2 increased clover foliage growth in the monocult ure by 19%, and by 31% in the mixture. Warming reduced clover monoculture h erbage production at ambient CO2 by 28% and reduced the growth enhancement by elevated CO2 to +8%. Forage growth of phalaris monoculture was not affec ted significantly by either factor. Forage growth of the mixture was increa sed by 34% in response to higher CO2, but unaffected by warming. Elevated C O2 combined with warming increased forage growth of the mixed sward by 23%. Concurrent rise in atmospheric CO2 concentration and temperature increased productivity of subterranean clover-phalaris swards. However, longer term e ffects on species competition and persistence may modify this conclusion.