Feeding the growing global population is one of the world's greatest challenges and drives the need for sustained increases in crop yields. Rising atmospheric carbon dioxide (CO₂) concentrations under future climate conditions have long been expected to boost productivity through the CO₂ fertilization effect, particularly for staple crops such as rice, on which billions of people depend. A new study shows that this effect may change substantially across generations exposed to elevated CO₂.

Over the past two decades, the CO₂ fertilization effect on rice growth and yield has been examined using free-air CO₂ enrichment (FACE) experiments spanning one generation. However, in a future high-CO₂ world, crops will be grown generation after generation under elevated CO₂ conditions. This raises a critical question: Can the fertilization effect be sustained over multiple generations?

A research team led by Prof. ZHU Chunwu from the Institute of Soil Science of the Chinese Academy of Sciences reports that the CO₂ fertilization effect on rice growth and yield depends heavily on the number of generations exposed to elevated CO₂ conditions. Accurately predicting rice productivity in a future high-CO₂ world requires studying the effect of multigenerational exposure to elevated CO₂ on rice yield.

The results were published in One Earth on January 16.

In this study, the researchers collected seeds of two rice cultivars, W23 (Wuyungeng 23, a japonica subspecies) and Y6 (Yangdao 6, an indica subspecies), which had experienced five to six growing seasons of ambient CO₂ and/or elevated CO₂. The researchers then planted these seeds in both ambient and elevated CO₂ environments in FACE experiments.

According to the researchers, 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 an increasing number of maternal elevated CO₂ generations. Due to 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 the transcriptome had changed and if epigenetic changes were responsible for rice nitrogen status, growth and yield in response to multigenerational exposure to elevated CO₂," said Assistant Prof. CAI Chuang, first author of the study. Understanding the epigenetic effects may be crucial for refining crop models to accurately predict rice yield in a future high-CO₂ world.

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

The results showed that data from single-generation exposure to elevated CO₂ in free-air CO₂ enrichment (FACE) experiments conducted over the past several decades cannot reliably predict the long-term response of rice yield to elevated CO₂ in a future high-CO₂ environment. Current crop models that ignore multigenerational effects of elevated CO₂ will lead to significant errors in predicting rice's response to a future high-CO₂ environment.

"Incorporating the epigenetic mechanisms of DNA methylation and the transcriptome into crop models to account for the multigenerational effects of elevated CO₂ is essential to accurately predicting future rice yields," said Prof. ZHU.

Whether these findings extend to other crops, such as wheat and soybeans, remains to be tested. Therefore, the researchers 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)