THE CRITICAL INFLUENCE OF TEMPERATURE ON THE INHIBITION OF PHOTOSYNTHESIS BY OXIDES OF NITROGEN IN LETTUCE.

The photosynthetic response of lettuce to the oxides of nitrogen (NO_x) generated during enrichment with CO₂ has been studied at different temperatures.
The steady rates of net photosynthesis of lettuce fell within several minutes following the addition of nitric oxide to the cuvette.
This did not appear to have been caused by a reduction in the stomatal conductance.
Removal of the pollutant gas resulted in a rapid and complete recovery in the rate of photosynthesis.
Gas exchange by a small stand of lettuce was measured in a novel growth chamber with fine thermal control.
In high CO₂ (1000 vpm) and at 16, 10 and 6° C a transient fumigation with 2.0 vpm NO reduced CO₂ uptake by 7, 11 and 29% respectively.
Deposition of NO into the canopy was 46% less at 6° than at 16°C. Uptake of the pollutant, therefore, did not explain the increased inhibition of photosynthesis.
The greater damage at low temperature may be due to a reduced capacity to metabolize some toxic products of NO_x assimilation.
Methods of CO₂ enrichment which vent the flue gases from the burners directly into the glasshouse air may not be entirely suitable for winter crops grown at low temperatures.

IV International Symposium on CO2 in Protected Cultivation

S.J.M. Caporn, T.A. Mansfield, D.W. Hand

https://doi.org/10.17660/ActaHortic.1990.268.8