Mineral nutrient deficiency increases the sensitivity of photosynthesis to sulphur dioxide in needles of a coniferous tree, Abies nordmanniana.

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Abies nordmanniana (Stev.) Spach was cultivated in rooting media either rich in nutrients (control) or low in magnesium (low Mg) or low in magnesium and nitrogen (low Mg-N), respectively. Intact, attached needles were exposed, in the light (460 μmol photons m-2 s-1), to an atmosphere containing 1 ppm SO2 for 5 h. Measurements of light- and CO2-saturated rates of photosynthetic O2 evolution, A max, were performed before and after SO2 treatments. In needles from well fertilized plants, A max was high (about 50 μmol m-2 s-1) and was not affected by SO2. Needles from low-Mg and low-Mg-N plants had lower photosynthetic rates and showed a marked decline in A max in response to the SO2 treatment. Stomatal conductance was similar in the three groups of plants during SO2 treatments.