Response of radish to multiple stresses: I. Physiological and growth responses to changes in ozone and nitrogen

Experiments were conducted to determine the impact of nitrogen and ozone (O₃ ) stress on the growth of domestic radish Raphanus sativus L. cv. Cherry Belle. Plants were grown in field chambers with sub-, optimal and supra-optimal levels of nitrogenous fertilizer. Chamber air was either charcoal-filtered, or supplemented with one of two levels of O₃ . The highest O₃ treatment resulted in significant reduction in weight of hypocotyls and roots while elevated nitrogen treatments resulted in increased weight of all plant parts. Ozone did not affect the weight of plant foliage at any nitrogen level. Plants grown with lower levels of nitrogen had less leaf biomass but the tissue accounted for a greater percentage total weight than did the foliage of higher nitrogen treatments. Relative growth rate of whole plants was not affected by O₃ or nitrogen treatments reflecting compensation in response to both stresses. Ozone-induced depression in biomass was observed in O₃ -treated plants grown with higher nitrogen supply but not in those grown with limiting nitrogen. This observation could reflect compensation at the lower levels of nitrogen supply or inability to detect changes in biomass due to reduced weights of plants grown at the lowest nitrogen supply. The dry weight ratio of sink organs (hypocotyl plus root)/shoot was significantly correlated with the total non-structural carbohydrate (TNC) content of these organs, regardless of treatment. Initially, O₃ induced a significant decrease and nitrogen an increase in percent TNC of sink organs. At later sampling times, plants adjusted to stress as effects on percent TNC were no longer evident.