Feeding the growing population is one of the greatest challenges and calls for increasing global crop yields. Rising atmospheric CO2 concentration under future climate conditions offers opportunities to increase yields via the CO2 fertilization effect on crops such as rice, which billions depend on.

The CO2 fertilization effect on the rice growth and yield has been studied in the past 20 years in FACE (free-air CO2 enrichment) experiments over a single-generation. However, in the future high-CO2 world, crops will be grown generation after generation under elevated CO2 conditions. Whether the CO2 fertilization effect can be sustained over multiple generations remains unclear.

The research team, led by Prof. ZHU Chunwu from the Institute of Soil Science of the Chinese Academy of Sciences (ISSCAS), reveals that the CO2 fertilization effect on rice growth and yield strongly depends on the number of generations in maternal elevated CO2. Accurate prediction of rice productivity in a future high-CO2 world requires the study of the effect on rice yield of multigenerational exposure to elevated CO2.

In this study, the researchers collected seeds of two rice cultivars, W23 (Wuyungeng 23, japonica subspecies) and Y6 (Yangdao 6, indica subspecies), that had experienced 5-6 growing seasons of ambient CO2 and/or elevated CO2 and planted these seeds into both ambient CO2 and elevated CO2 environments in FACE experiments. The results, published in One Earth, demonstrate that the CO2 fertilization effects on aboveground biomass, aboveground nitrogen uptake, and grain yield were initially higher for cv. Y6 than for cv. W23. However, the CO2 fertilization effects decreased for cv. Y6, but increased for cv. W23, with the increasing number of maternal elevated CO2 generations. Because of these opposite trends, the CO2 fertilization effects on aboveground biomass, aboveground nitrogen uptake, and grain yield became higher in cv. W23 than in cv. Y6 after 5-6 generations of exposure to maternal elevated CO2 environments.

"We wondered whether DNA methylation and transcriptome were altered and whether there were epigenetic changes responsible for rice nitrogen status, growth and yield in response to multigenerational exposure to elevated CO2. Understanding the epigenetic effect may be crucial for refining crop models to accurately predict rice yield in a future high-CO2 world,." said Assistant Prof. CAI Chuang, first author of the study from ISSCAS.

Integrated analysis confirmed that DNA methylation and transcriptome exhibited opposite trends between the two cultivars in relation to the multigenerational effect of eCO2, providing epigenetic evidence on opposite trends in the CO2 fertilization effects on aboveground biomass, aboveground nitrogen uptake and yield.

"Our results highlighted that data from single-generation exposure to elevated CO2 in FACE experiments conducted in the past several decades cannot be used to reliably predict long-term responses of rice yield to elevated CO2 in the future high-CO2 world. Current crop models that ignore the multigenerational effects of elevated CO2 will result in critical errors in predicting rice responses to the future high-CO2 environment. Incorporating epigenetic mechanisms of DNA methylation and transcriptome for the multigenerational effect of elevated CO2 into crop models is essential to accurately predict future rice yield," said Prof. ZHU.

Whether these findings extend to other crops like wheat and soybean remains to be tested. The researchers therefore call for more multigenerational FACE experiments on a wider range of crops. Such studies are essential to refine predictions, guide adaptation strategies, and ultimately, secure global food production for our high-CO2 world.

Rice responses to single-generation and multigenerational exposure to elevated CO2 (Image by ZHU Chunwu’s team)