The Effect of Nitric Oxide Fumigation at Two CO2Concentrations on Net Photosynthesis and Stomatal Resistance of Tomato (Lycopersicon lycopersicum L. cv. Abunda)

Net photosynthesis of 5-week-old tomato plants (Lycopersicon lycopersicum L. cv Abunda), was measured in clean air or with NO fumigation, for five consecutive days under simulated winter glasshouse conditions. temperature 22⚬C, VPD 0.4 kPa, irradiance 30 W m-2and daylength 8-9 h. NO concentrations applied were 0 or 1 μ l l-1in combination with CO2concentrations of 350 or 1000 μ l l-1. A reduction in net photosynthesis due to NO became apparent on the third day of measurement. On the fifth day this reduction was 38% of the control at 350 μ l l-1CO2and 24% at 1000 μ l l-1CO2. The increase in photosynthesis due to CO2enrichment was initially 40%, this effect was strongly reduced after 5 d in the presence of NO Plants did not recover in the dark after the daily fumigation treatment, the level to which photosynthesis was reduced at the end of the day being the level at which it started the next day. The decrease in photosynthesis could not be explained by an increased stomatal resistance, and the plants did not show visible symptoms of injury Practical implications of the results are discussed.