Effects of NaCl salinity on nitrate uptake and partitioning of N and C in Festuca rubra L. in relation to growth rate

The effect of salinity on nitrate net uptake rate was studied in the moderately salt tolerant halophyte Festuca rubra L., in relation to changes in relative growth rate, root weight ratio and nitrogen and carbon partitioning. Plants were grown for 21 days on nutrient solution containing 50, 100 and 200 Mol m(-3) sodium chloride. Control plants received no additional sodium chloride. Relative growth rate of Festuca rubra was reduced by exposure to a sodium chloride concentration as low as 50 mol m-3, resulting in a lower nitrogen 'demand' for plant growth and consequently in a lower nitrate net uptake rate. However, the accumulation of reduced nitrogen containing osmotic solutes increased the plant's nitrogen 'demand' slightly The decreased root weight ratio, caused by the stronger inhibition of root growth as compared to shoot growth upon elevated salinity levels complicated the interpretation of the effects of different salinity treatments on nitrate net uptake rates. Utilization of soluble sugars for osmotic adjustment did not divert significant amounts of carbohydrates from the carbon pool. To get insight into the physiological background of the interaction between sodium chloride salinity and nitrate uptake, additional complications in the growth analysis and N nutrition must be considered

Spatial patterns of radial oxygen loss and nitrate net flux along adventitious roots of rice raised in aerated or stagnant solution

Roots of rice (Oryza sativa L.) grown in stagnant de-oxygenated solution contain a 'tight' barrier to radial oxygen loss (ROL) in basal zones, whereas roots of plants grown in aerated solution do not. It is generally accepted that the barrier to ROL involves anatomical modifications in the apoplast of cell layers exterior to the aerenchyma. A possible drawback of this adaptation is a reduced capacity for nutrient uptake. Whether or not induction of a barrier to ROL influences the capacity of adventitious roots of rice to take up NO3- was determined in the present study, using NO3--selective microelectrodes. When transferred into O-2-free root medium, ROL from positions at 30-50 mm behind the tip of adventitious roots of plants raised in stagnant solution was only 4-6% of the rate from roots of plants raised in aerated solution, indicating the barrier to ROL was induced by growth in stagnant solution. For plants transferred into aerobic nutrient solution containing 0.1 mM NO3-, net NO3- uptake by these root zones, with or without a barrier to ROL, was the same. It is concluded that induction of a barrier to ROL had no effect on the capacity of adventitious roots of rice to take up NO3- from aerobic solution