The Effect of Long Term Exposition of Poplars to Low Concentrations of SO2 and NH3

Abstract

Young cuts of poplar (P. euramericana L.) were exposed to concentrations of SO2 and NH3 which are considered normal for certain areas in the Netherlands. The effect of 7 weeks of this treatment was monitored with the modulated fluorescence technique and with gas exchange measurements. Photosynthetic performance during the development of the leaves was also followed with the fluorescence technique. The effect of the fumigation on these stress-’free’ plants was relatively small in comparison to the developmental changes during the 7 weeks of observation and treatment. The photosynthesis measurements revealed a slight increase in light efficiency for the higher concentrations of NH3 and SO2. However this increase was absent when the two gasses were combined. NH3 also revealed an increased Pmax. Fluorescence measurements only revealed an enhanced non-photochemical quenching component under steady state conditions for the NH3 treatment. The SO2 treatment revealed enhanced activation kinetics of the CO2 fixation process (Calvin cycle). When the 2 measurements are combined it becomes evident that the higher SO2 concentration (37.2 ppb) and the NH3 treatment (129 ppb) enhance the quantum yield of photosystem 2 for photochemistry under the condition of an ‘energized’ thylakoid membrane. It is therefore concluded that low concentrations of these air pollutants are able to induce a more pronounced state of sun adaptation (Bjorkman 1981) than their counter parts, which had received either filtered air, a low SO2 concentration (18.8 ppb) or a combination of SO2 and NH3.