EFFECTS OF NO, NO₂ AND CO₂ ON NET PHOTOSYNTHESIS, DARK RESPIRATION AND TRANSPIRATION OF POT PLANTS

Abstract

SUMMARY Eight cultivars of the pot plants (Ficus elastica ‘Rdobusta’, Ficus benjamina, Hedera helix ‘Anne Marie’, Hedera canariensis‘Montgomery’, Hibiscus rosa‐sinensis‘Red’, Hibiscus rosa‐sinensis‘Moesiana’, Dieffenbachia maculata‘Compacta’ and Nephrolepis exaltata‘Bostoniensis’) most commonly grown in Danish commercial greenhouses were subjected to 4 d exposures to 1 ml 1 −1 of CO 2 , 1 ml 1 −1 CO 2 + 1 μ 1 −1 NO, 1 μ 1 −1 NO alone and 1 μ 1 −1 NO 2 alone. Effects on net photosynthesis and dark respiration of aerial parts and effects on whole plant transpiration were observed before, during and after exposures. The measurements were mathematically transformed to double relative values, to indicate the effects of the different gaseous treatments. Carbon dioxide enrichment enhanced net photosynthesis by 40–9 % and subsequent dark respiration by 235 %, while transpiration was reduced. NO reduced photosynthesis (approximately 20 %) and transpiration (the latter at high CO 2 only), but did not affect respiration. NO 2 rarely had significant effects. All effects of the gaseous treatments on photosynthesis and transpiration were reversible and had independent mechanisms, while effects on respiration were non‐reversible. On the average, 1 μ 1 −1 NO was four times more inhibitory to photosynthesis than 1 μ 1 −1 NO 2 . Short‐term effects (4 d) on photosynthesis of exposure to CO 2 + NO correlated significantly (P < 0.03) with the long‐term effects (four to five months) on dry weight found using the same cultivars in similar treatments.