Inhibition of nitrate uptake and assimilation in wheat seedlings grown under elevated CO2

Wheat (Triticum aestivum L.) cv PBW 343 was grown in Hoagland solution devoid of nitrogen (-N) under two CO2 levels viz. ambient (380 μL L-1, AC) and elevated (600 ± 50 μL L-1, EC) for 20 days in growth chambers. The rate of uptake, assimilation and accumulation of nitrate was compared. At lows nitrate concentration up to 0.5 mM, rate of nitrate uptake was higher in EC grown seedlings as compared to AC. Under non-limiting supply of external nitrate, the rate of uptake declined in EC grown seedlings. Nitrate reductase (NR) activity increased in EC grown seedlings at low external concentrations of nitrate. However, AC grown plants showed higher NR activity, but at very high concentrations of nitrate. EC grown plants showed low level of accumulation of nitrate in shoots under limited nitrate availability, indicating lower influx towards storage pool and more availability of nitrate in metabolic pool. Increasing nitrogen (N) fertilization therefore may not compensate for slower NO3}- assimilation rates under EC, as uptake and assimilation both decline under nitrate sufficient conditions. Effective management practices and changes in the pattern of fertigation may be required in response to rising atmospheric CO2 levels for wheat production. © 2013 Indian Society for Plant Physiology.