Enhancing Japonica Rice Yield Under Elevated CO2: Addressing Limitations and Strategies

Abstract

Elevated CO₂ enhances photosynthesis and yield in rice, with indica rice generally displaying a stronger yield response than japonica. However, uncertainty remains about the key yield components driving this difference, which limits breeding strategies for enhancing japonica rice yield. To identify critical factors in yield responses to elevated CO₂ and to explore potential improvements in japonica rice yield, we conducted a meta-analysis of FACE (Free-Air Carbon dioxide Enrichment) data from China and Japan to examine yield component contributions. Additionally, we investigated whether rice lines with enlarged root systems could enhance yield response to elevated CO₂ (+200 μmol mol⁻¹). Our results indicated that, under elevated CO₂, Chinese indica rice genotypes achieved a substantial grain yield increase, averaging around 31.1%. On the other hand, the Chinese and Japanese japonica along with the Japanese indica demonstrated more moderate increases, measuring about 10.3%, 13.7% and 12.5%, respectively. Among yield components, spikelets per panicle (SPP), often a lagging indicator, was identified as a crucial factor in further increasing yield potential. OsERF3-overexpressing rice lines not only expanded root growth but also stimulated root vigour under elevated CO₂ conditions. These enlarged-root lines demonstrated improved nutrient uptake, nitrogen-content stability, increased photosynthesis rates and greater grain weight, effectively avoiding the SPP reductions typically seen in Chinese japonica under elevated CO₂. As a result, these lines achieved a 38.6% yield increase under elevated CO₂, outperforming wild-type japonica responses. These findings suggest that enlarged-root rice lines could be a promising breeding platform for enhancing rice production and developing climate-resilient rice cultivars.