Elevated atmospheric CO2 and warming enhance the acquisition of soil-derived nitrogen rather than urea fertilizer by rice cultivars

Plant nitrogen (N) acquisition is essential to both crop growth and yield. A rational N management strategy for agricultural systems under climate change is required but a knowledge gap still exists regarding plant N uptake and N origin (soil-derived N or fertilizer-derived N) in response to elevated atmospheric CO2 and warming. Our study investigated the responses of soil- or fertilizer-derived N uptake and yield of different cultivars of rice (Oryza sativa L.) to climate change. Five cultivars in the pedigree of a widely-grown rice cultivar Wuyoudao1 were supplied with and without urea, a commonly used N fertilizer in paddy soils and grown in open-top chambers under elevated CO2 (700 ppm) and warming (2°C higher than the air temperature). Plant N origins were traced using 15N-labeling technique (urea of 5% 15N atom). Compared to the control, elevated CO2 and warming increased N uptake by 17%, irrespective of N supply. Soil-N rather than fertilizer-N was the source of the increased N uptake. The increased soil-N uptake resulted in the enhancement of rice yield under climate change. Urea application did not alter the yield response to elevated CO2 and warming compared to the non-N supply, but did stimulate plant uptake of the soil-derived N. Although genetic improvement of rice germplasm resulted in an increase in plant N acquisition and yield, the history of crop breeding since 1935 did not alter the climate-change-induced response in terms of plant N acquisition. Our results suggest that climate change may lead to the depletion of the recalcitrant soil N pool in paddy soils, and that fertilizer-N-use efficiency may need to be factored into future breeding for rice genotypes adapting well to climate change.