Effects of ozone and ammonium sulphate on carbon partitioning to mycorrhizal roots of juvenile Douglas fir

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Abstract
In this study the impact of two components of air pollution, i.e., ozone and ammonium sulphate, on carbon transport to mycorrhizal roots of Douglas fir was investigated. Juvenile Douglas fir (Pseudulsuga menziesii [Mirb.] Franco) were inoculated with Rhizopogon vinicolor A. H. Smith and Lactarius rufus (Scop.: Fr.) Fr., and allowed to grow outdoors for a period of four months. Subsequently, they were transferred to a phytotron and treated with 0 or 200μg m−3 ozone for 28 days. During these treatments, they were watered with a solution of ammonium sulphate of concentrations corresponding to 5, SO and 200 kg N ha−1 yr−1, During the last three days, the trees were pulse‐labelled with 14CO2. Ozone increased the amounts of 14C recovered in the new needle fraction, whereas the amounts recovered in the roots and root/soil respiration tended to decrease. Mycorrhizal frequency tended to increase during ozone treatment. Ammonium sulphate did not affect the distribution pattern of 14C over the trees, but seemed to stimulate the activity of the root system and mycorrhizal frequency at the intermediate nitrogen level.