Effect of enriched rhizosphere carbon dioxide on nitrate and ammonium uptake in hydroponically grown tomato plants

Previous reports have indicated positive effects of enriched rhizosphere dissolved inorganic carbon on the growth of salinity-stressed tomato (Lycopersicon esculentum L. Mill. cv. F144) plants. In the present work we tested whether a supply of CO2 enriched air to the roots of hydroponically grown tomato plants had an effect on nitrogen uptake in these plants. Uptake was followed over periods of 6 to 12 hours and measured as the depletion of nitrogen from the nutrient solution aerated with either ambient or CO2 enriched air. Enriched rhizosphere CO2 treatments (5000 μmol mol-1) increased NO3- uptake up to 30% at pH 5.8 in hydroponically grown tomato plants compared to control treatments aerated with ambient CO2 (360 μmol mol-1). Enriched rhizosphere CO2 treatments had no effect on NH3+ uptake. Acetazolamide, an inhibitor of apoplastic carbonic anhydrase, increased NO3- uptake in ambient rhizosphere CO2 treatments, but had no effect on NO3- uptake in enriched rhizosphere CO2 treatments. Ethoxyzolamide, an inhibitor of both cytoplasmic and extracellular carbonic anhydrase, decreased NO3- uptake in ambient rhizosphere CO2 treatments. In contrast, a CO2 enriched rhizosphere increased NO3- uptake with ethoxyzolamide, although not to the same extent as in plants without ethoxyzolamide. It is suggested that a supply of enriched CO2 to the rhizosphere influenced NO3- uptake through the formation of increased amounts of HCO3- in the cytosol.