Effect of simulated acidic fog on carbohydrate leaching, CO 2 assimilation and development of damage symptoms in young spruce trees ( Picea abies L. Karst)

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The effect of acidic fog on carbohydrate leaching, CO 2 assimilation, carbohydrate status, and cuticle development of young spruce trees was studied in a greenhouse experiment. Over a period of 9 weeks the plants were subjected to fog application on 27 occasions. In one treatment trees were exposed to a fog of pH 2.75 (acidic fog) and in one treatment to a fog of pH 5.00 (control treatment). Leaching rates for carbohydrates (sucrose, glucose, fructose) were significantly higher in the acidic fog treatment than in the control treatment. The total amount of carbohydrates leached out of the trees by acidic fog, however, was low and amounted to less than 1% of the non-structural carbohydrates in the needles. Trees which had been exposed to acidic fog were not affected in photosynthesis and in the distribution of photosynthates to various plant parts. In the younger needles significantly lower concentrations of starch, glucose, and fructose were found in the treatment with acidic fog as compared with the control plants. Also the starch concentration in the roots of the control plants was significantly higher than that in the plants exposed to acidic fog. These findings are suggestive of a stress situation with a high energy demand. Application of acidic fog resulted in a disintegration of the epicuticular wax layer and of the epistomatal wax props. In the treatment with acidic fog some needles of the current year turned reddish-brown and some older needles became chlorotic and later brown. These needles were shed to a large degree. Needle loss of the trees exposed to acidic fog was significantly higher than that of the control trees.