Impact of elevated CO2 concentration on inter-subspecific hybrid rice cultivar Liangyoupeijiu under fully open-air field conditions

Hybrid rice cultivar plays an important role in rice production system due to its high yield potential and resistance to environmental stress. Quantification of its responses to rising CO₂ concentration ([CO₂]) will reduce our uncertainty in predicting future food security and assist in development of adaptation strategies. Using free air CO₂ enrichment (FACE), we measured seasonal changes in growth and nitrogen (N) uptake of an inter-subspecific hybrid rice cultivar Liangyoupeijiu grown under two levels of [CO₂] (ambient and elevated by 200 μmol mol⁻¹) and two levels of N fertilization in 2005–2006. Average across the 2 years, FACE increased crop growth rate similarly by 22%, 24% and 23% in the periods from transplanting to panicle initiation (PI), PI to heading and heading to maturity, which was mainly attributed to an increase in green leaf area index rather than the greater net assimilation rate. Grain yield increased greatly under FACE as a result of similar contributions by panicle number per unit area, grain number per panicle and individual grain yield. Final aboveground N acquisition showed a 10.4% increase under FACE, which resulted from enhanced N uptake at both vegetative and reproductive growth stages. Compared with previous FACE studies on final productivity of two inbred japonica cultivars, inter-subspecific hybrid cultivar appears to profit more from elevated [CO₂], which mainly resulted from its greater enhancement in photosynthetic production during reproductive growth due to a lack of N limitations late in the season.