INFLUENCE OF ELEVATED CO2 AND PHOSPHORUS-NUTRITION ON THE GROWTH AND YIELD OF A SHORT-DURATION RICE (ORYZA-SATIVA L CV JARRAH)

The growth and development of a short-duration rice cultivar (Oryza sa tiva L. cv. Jarrah), grown in flooded soil with a range of phosphorus (P) levels and exposed to atmospheric CO2 concentrations of either 350 or 700 mu L L(-1) was followed for 146 days after planting (DAP). Dev elopment (estimated by rate of tiller production and time to flowering ) was faster with higher soil P levels and CO2 enrichment, the effect being more pronounced with CO2 enrichment. During the early vegetative phase (up to 35 DAP), when rates of tiller production were low, shoot growth and rates of leaf expansion were faster at elevated CO2 concen trations and high soil P levels. Rates of tiller production were great er with these treatments during the 35-56 DAP period, when tillering w as at a maximum. Shoot elongation was reduced at elevated CO2 levels a nd at high soil P levels during this period. By 146 DAP leaf weight wa s greater at high P levels, but CO2 enrichment accelerated tiller prod uction to such an extent that final leaf weight was lower at high CO2, probably because there were fewer, and smaller, leaves on each tiller . Despite this, grain yield was increased by up to 58% by CO2 enrichme nt, with increases occurring even at low soil P levels. This was due m ainly to an increase in grain number per panicle, although panicle num ber also increased. Higher soil P levels also increased grain number a nd yield. The P concentration in the foliage was unaffected by the CO2 treatments and the concentration required to produce maximum yield wa s 0.18% (dry wt basis) at both CO2 levels. Greater starch accumulation in the stems of high-CO2-grown plants may have accounted for the high er number of grains in each panicle.