INFLUENCE OF RISING ATMOSPHERIC CO2 AND PHOSPHORUS-NUTRITION ON THE GRAIN-YIELD AND QUALITY OF RICE (ORYZA-SATIVA CV. JARRAH)

Raising the atmospheric CO2 concentration from 350 mu l of CO2 per lit er to a level expected by the end of the next century (700 mu l/L) inf luenced both the grain yield and quality of the short-duration rice (O ryza sativa) cultivar, Jarrah. Yield was enhanced by up to 58%, primar ily due to an increase in grain number, although grain size was also g reater at high CO2. Varying the supply of phosphorus influenced the ma gnitude of the CO2 response with greatest responses occurring at mediu m rather than luxury or low phosphorus supplies. However, yield enhanc ement by high CO2 was observed even when phosphorus supply was severel y growth limiting. Chemical (amylose and nutrient concentration) and p hysical (relative paste viscosity) measurements made on the ground gra in indicated that cooked rice grain from plants grown under high level s of CO2 would be firmer. The nutritive value of grain was also change d at high CO2 due to a reduction in grain nitrogen and, therefore, pro tein concentration. However, total nitrogen content per grain was unaf fected by high CO2. In contrast, phosphorus content per grain was grea ter at high CO2 and there was a strong correlation between magnesium a nd phosphorus concentrations. These results indicate that there is a n eed to plan for the inevitable rise in atmospheric CO2 concentrations by selecting genotypes that will maintain suitable quality characteris tics under global change.