Benefits of CO 2 Fertilization on Global Grassland Nitrogen Cycles

Grasslands are vital for providing wildlife habitats, essential ecosystem services, and food to humanity. Elevated atmospheric CO 2 concentration (eCO 2 ), as a key driver of climate change, has substantial effects on grasslands. Nonetheless, a holistic quantification on the response of the nitrogen cycle to eCO 2 in global grasslands is lacking. Here, we show that solely eCO 2 could increase the net primary productivity (NPP) in grasslands by 10% (95% confidence interval, 8–12%), yet simultaneously decrease leaf nitrogen content by 8% (95% confidence interval, 5–10%). When considering the effects of eCO 2 on both NPP and leaf nitrogen content, we estimate a projected increase of 2.1 million tonnes per year (Tg yr –1 ) in nitrogen harvest by global grasslands under the eCO 2 SSP2-4.5 scenario in 2050. The increase in nitrogen use efficiency by 29% (95% confidence interval, 18–40%) and biological nitrogen fixation by 66% (95% confidence interval, 18–138%) would lead to declines in nitrogen surplus (−28.3 Tg yr –1 ). These changes in the grassland nitrogen budget due to eCO 2 would generate benefits to 158 billion US dollars by avoiding human and ecosystem health damages. Priority should be accorded to sustainable nitrogen management strategies to leverage the advantages of CO 2 fertilization for ensuring food security and mitigating nitrogen pollution.