Changes in carbohydrates, leaf pigments and yield in potatoes induced by different ozone exposure regimes

Potatoes (Solanum tuberosum cv. 'Hela') were exposed in closed fumigation c hambers for nine weeks until harvest in 1995. In three treatments ozone was applied as constant concentration (35 ppb for 24 h/d) as well as with peak s (110 ppb for 4 h/d and 65 ppb for 8 h/d) under equal dose conditions. In addition ozone was applied at constant concentration (47, 65 ppb for 24 Nd) in two treatments. In 1996 potatoes were exposed for six weeks and kept un til harvest for four weeks in charcoal filtered ambient air (<5 ppb). Ozone was applied as constant concentration (65 ppb for 24 Nd) as well as with p eaks (110 ppb for 4 h/d). In both years plants in control chambers were cul tivated in charcoal filtered ambient air (<5 ppb). Effects of the different treatments on pigment and carbohydrate (hexoses, sucrose, starch) content in leaves and/or tubers during and after exposure were determined and fresh tuber weight was assessed. Effects on physiological parameters, a decrease in sucrose up to 43% relative to control (p < 0.05, 65 ppb for 24 Nd) and pigment content up to 25% relative to control (p < 0.001, 65 ppb for 24 h/d ) of leaves were induced after four weeks of exposure. Under equal dose con ditions (1995) ozone peaks induced much more pronounced effects on carbohyd rate content than constant concentrations. Glucose content in leaves decrea sed after eight weeks of exposure to 65 ppb (8 Nd) resp. 110 (4 h/d) about 67% (p < 0.001) resp. 62% (p < 0.01) in comparison with a decrease of about 43% (p < 0.05) after exposure to 35 ppb (24 Nd). Similar observations were made with respect to tuber weight which decreased up to 20% (p < 0.01) aft er exposure to 110 ppb peaks (4 h/d) and a four week period in charcoal fil tered air (<5 ppb). This was similar to the decrease of 26% (p < 0.001) aft er exposure to 65 ppb constantly, the daily dose being doubled (1996). The results favour the hypothesis that ozone peaks induce much stronger eff ects than constant concentrations using the same total dose and that effect s of ozone treatment are carried over fur weeks in periods of relatively lo w ozone levels with respect to tuber weight as well as carbohydrate content . (C) 2000 Elsevier Science B.V. All rights reserved.