Benefits of CO2 fertilization on global grassland nitrogen cycles

Grasslands provide wildlife habitats, essential ecosystem services and food to humanity. Elevated atmospheric CO 2 concentrations (eCO 2 ) are a major climate change driver and have substantial effects on grasslands. Nonetheless, the grassland nitrogen cycle response to eCO 2 largely remains unknown. Here we show that eCO 2 alone could increase the net primary productivity by 10% (95% confidence interval, 8% to 12%) but decrease leaf nitrogen content by 8% (95% confidence interval, 5% to 10%), leading to a projected 4 million tonnes per year (Tg yr −1 ) increase in nitrogen uptake by global grasslands under the eCO 2 SSP2-4.5 scenario by 2050. Total nitrogen input to global grasslands is expected to decrease by 24 Tg yr −1 , while biological nitrogen fixation would increase by 9 Tg yr −1 . The increase in nitrogen use efficiency by 29% (95% confidence interval, 18% to 40%) would lead to declines in nitrogen fertilizer use (-16 Tg yr −1 ) and nitrogen surplus (-28 Tg yr −1 ). These changes in the grassland nitrogen budget due to eCO 2 would generate benefits to a value of 189 billion US dollars by avoiding human and ecosystem health damage costs. The positive effects should be considered in the development of effective management strategies for climate change adaptation and to foster sustainable development.