Nitrogen resorption in senescing leaf blades of rice exposed to free-air CO2 enrichment (FACE) under different N fertilization levels

Nitrogen (N) resorption from senescing leaves is essential to meet N demand for grain development in rice (Oryza sativa L.). We asked whether rice is capable of reducing N in their senesced leaf blade to lower concentration at elevated [CO2] more in low than in high N fertilization. The effects of elevated [CO2] and N fertilization on senesced leaf N concentration were examined for 3 years with the free-air CO2 enrichment (FACE) technology. Elevated [CO2] decreased the senesced leaf N concentration but the change was generally small and did not hold over the growing seasons. Additionally, there was no evidence that the change was greater at low than at high N fertilization levels. The 3-year field measurements showed that elevated [CO2] did not change the senesced leaf N concentration consistently. The occasional decrease in senesced leaf N concentration was associated with a decrease in green leaf N concentration at elevated [CO2] but not with the proportion of leaf N resorbed during leaf senescence.