NITROGEN OXIDES PRODUCED DURING CO2 ENRICHMENT III. EFFECTS ON TOMATO AT DIFFERENT PHOTON FLUX DENSITIES*

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Abstract
Seedlings of Lycopersicon esculentum (tomato) were subjected to CO2-enriched air (1000 .mu.l l-1) containing 1.5 .mu.l l-1 nitrogen oxides (NOx) for 25 d at four photon flex densities (30, 95, 175 and 250 .mu.mol m-2 s-1, PAR). CO2 enrichment without NOx significantly increased the dry weights (47 to 93%) at all light levels. Addition of NOx strongly reduced the mean dry weight at the lowest light level even below that of the unenriched control. At the two highest light levels, NOx reduced the dry weight, but much less than at the lowest level. NOx caused severe leaf injury at the lowest light level, but this effect disappeared with increased photon flux density. A system was constructed for measurement of the net CO2 exchange rate (CER) for single plants. Short-term measurements showed significant reductions of CER when the NO concentration was increased from 0 to 9 .mu.l l-1 at 550 .mu.mol m-2 s-1 but almost no effect at 140 to 200 .mu.mol m-2 s-1. NO caused similar percentage reductions of CER at 335 and 1000 .mu.l l-1 CO2. The absorption of NO was not significantly affected by increasing the photon flux density from 150 to 550 .mu.mol m-2 s-1.