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

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.