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SUMMARY Relations between above‐ground fruitbodies of mycorrhizal fungi and mycorrhizas in the soil were studied in 23 Douglas fir stands of various ages in The Netherlands. In the autumn of 1986, fruitbody and mycorrhiza density and diversity were determined. Quantitative relations were found between above‐ground fruitbodies of mycorrhizal fungi and below‐ground mycorrhizas. Mycorrhiza density explains fruitbody density better than mycorrhiza frequency, but fruitbody density is an unreliable estimator of mycorrhiza density. Density of root tips does not influence the density of fruitbodies. The above‐ground diversity, in number of species of fruitbodies, is reflected by the below‐ground diversity, in number of mycorrhiza types, but the below‐ground diversity is not explained simply by the number of species fruiting. The strong decline in density and diversity of fruitbodies and mycorrhizas with age of the stands cannot be explained yet.

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SUMMARYIn this study the impact of two components of air pollution, i.e., ozone and ammonium sulphate, on carbon transport to mycorrbizal roots of Douglas fir was investigated. Juvenile Douglas fir {Pseudotsuga 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 200//.g m~^ ozone for 28 days. During these treatments, they were watered with a solution of ammonium sulphate of concentrations corresponding to 5, 50 and 200 kg N ha"' yr"^ During the last three days, the trees were pulse-labelled with ^^CO,,. Ozone increased tbe amounts of '^C recovered in the new needle fraction, whereas the amounts recovered in the roots and root/soil respiration tended to decrease. Mycorrhiza] frequency tended to increase during ozone treatment. Ammonium sulphate did not affect the distribution pattern of ^*C over the trees, but seemed to stimulate tbe acti^'ity of the root system and mycorrhizal frequency at the intermediate nitrogen level.

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