Influence of Elevated CO₂ and Phosphorus Nutrition on the Growth and Yield of a Short-Duration Rice (Oryza sativa L. Cv. Jarrah)

Abstract

The growth and development of a short-duration rice cultivar (Oryza sativa 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 μL L^-1 was followed for 146 days after planting (DAP). Development (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 concentrations and high soil P levels. Rates of tiller production were greater with these treatments during the 35-56 DAP period, when tillering was at a maximum. Shoot elongation was reduced at elevated CO₂ levels and at high soil P levels during this period. By 146 DAP leaf weight was greater at high P levels, but CO₂ enrichment accelerated tiller production 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 enrichment, with increases occurring even at low soil P levels. This was due mainly to an increase in grain number per panicle, although panicle number also increased. Higher soil P levels also increased grain number and yield. The P concentration in the foliage was unaffected by the CO₂ treatments and the concentration required to produce maximum yield was 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 higher number of grains in each panicle.