Fig. 1. (a) Two-dimensional microcosm (without the front acrylic plate; the thickness of the humus layer is 5 mm) photographed about two months after planting the Scots pine seedling (4.5 months old) infected with fungus Paxillus involutus. (b) Nonplanted microcosm. Note the mosses growing at the edges of the microcosms and mycorrhizas (marked with arrowheads). When the microcosms were about one month old, an area of 25 cm² (marked with asterisks) was excised (Region I) and replaced by an implant consisting of natural humus with pyrene (0 or 100 mg kg^–1) or a mixture of natural humus and waste oil soil as described in Table 1. The implanted microcosms were equilibrated in the growth room for one month. Then each implant was spiked with 0.2 g of humus containing 10⁵ disintegrations per minute (dpm) of ¹⁴C-pyrene (0.15 µg).