Catabolism of a C-14-labelled volatile monoterpene compound (geraniol) to (CO2)-C-14 was investigated in soils taken from the rhizosphere at distances up to 200 cm from the trunks of three small Populus tremula trees growing at different sites in Slovenia. Emissions of limonene of up to 18 mu g m(-2) h(-1) were detected from the soil surface at each site. Evolution of C-14-labelled CO2 was measured as a product of catabolism of C-14-labelled geraniol introduced into the soil samples. Indigenous soil microorganisms degraded the geraniol rapidly. There was a significant difference in relative lag times and rates of catabolism along the gradient from the tree trunks, with relatively longer lag times and lower rates occurring in soil samples from the farthest point from the tree.