A new explanation of the N concentration decrease in tissues of rice (Oryza sativa L.) exposed to elevated atmospheric pCO2

In this paper, four hypotheses to explain the N concentration decrease in plants exposed to elevated pCO2 were tested by growing rice (Oryza sativa L.) in nutrient solution under two atmospheric carbon dioxide (CO2) concentrations (ambient and ambient + 200 μmol mol−1) and two N levels (14 and 28 mg N L−1). Results showed that: (1) ‘dilution’ of N by enhanced biomass occurred in all tissues but leaves. (2) Elevated pCO2 favored N allocation to ears over to stems and leaves, however, altered N partition between the shoot and the root was not observed. (3) The decline in transpiration rate should not be the key factor that led to the reduction in plant tissue N concentration under elevated pCO2. (4) Significantly increased total plant N uptake under elevated pCO2 did not led to a significant increase of N yield due to increased plant N loss (defined as the difference between total N uptake and N yield). Elevated pCO2 also decreased root N uptake efficiency (NRE). Increased plant N loss and decreased NRE at elevated pCO2 may play major roles in N concentration decrease in tissues of rice.