Response of rice production to rising CO2 and its adaptive cultivation strategies

Rice is the staple food for more than half of the population in China. Therefore, enhancing the grain yield of rice is the core of ensuring food security. In recent decades, the increase of atmospheric carbon dioxide (CO₂) concentration generally increases the photosynthetic rate of rice and then the rice yield. This phenomenon is generally termed the CO₂ fertilization effect (CFE), which plays a pivotal role in sustaining global rice yield in the context of climate change. In order to accurately understand the impact of elevated CO₂ on rice productivity and yield, this study first presents the mechanisms of CFE impacts on rice yield at the foliar and canopy levels. Elevated CO₂ will promote the net photosynthetic rate, reduce the stomatal conductance, and thus increase the water use efficiency. Currently, at foliar, canopy, regional and global scales, controlled experiments, process-based models and statistical attribution models are the main approaches to estimate CFE. Based on these methods, at the leaf and canopy scales, elevated CO₂ will lead to an increase in the number of panicles per unit area and the spikelet number per panicle of rice, finally resulting in the enhancement of grain yield. State-of-the-art crop models suggested that the global averaged CFE on rice yield is about 24% per 100 ppm increase in CO₂, albeit with large differences between different models. Rice varieties, nutrient management, water regimes, planting density and temperature are the main factors that affect the CFE. Finally, based on the existing research basis and existing problems, we proposed several future research directions including the understanding of the mechanism of CFE from the perspective of rice roots, soil microbes, key genes and rice breeding, and also the upscaling of the results from site-level to regional- and global-level through the integration between experiments and models. By systematically reviewing the response of rice physiology and yield to elevated CO₂ using multiple methods at various scales, this study will be beneficial for the formulation of adaptive cultivation strategies to enhance the rice yield and thus to sustain global food security in the context of climate change.