Nitrogen cycles in global croplands altered by elevated CO2

Abstract Croplands support global food security and human nutrition, representing the largest nitrogen flows globally. Elevated atmospheric carbon dioxide (CO2) level is a key driver of climate change with multiple impacts on food security, environmental and human health. However, our understanding of how the cropland nitrogen cycle will respond to elevated CO2, so far is not well developed. We demonstrate that elevated CO2 alone would induce a synergistic intensification of the nitrogen and carbon cycles, promote nitrogen use efficiency by 19% (14-26%) and biological nitrogen fixation by 55% (28-85%) in global croplands. This would lead to increased crop nitrogen harvest (+12 Tg), substantially lower fertilizer input requirements (-34 Tg) and an overall decline in reactive nitrogen loss (-46 Tg) annually under future elevated CO2 scenarios by 2050. The impact of elevated atmospheric CO2 on altered cropland nitrogen cycle would amount to 672 billion US dollars benefit in terms of avoiding damages to human and ecosystem health. Regionally, the largest alteration would materialize in China, India, North America, and Europe. To improve the policy design for food security and sustainable development, it would be paramount to integrate the effect of rising CO2 on nitrogen cycle into state-of-the-art Earth System Models.