ACID DEPOSITION IN A SPRUCE FOREST SOIL - EFFECTS ON NEMATODES, MYCORRHIZAS AND FUNGAL BIOMASS

The belowground biota (nematodes, fungal biomass, roots and mycorrhiza l development) of a mature Sitka spruce stand under the influence of a cid precipitation (equimolar sulphuric acid and ammonium nitrate) was investigated. Sampling took place after 3 years of treatment and 5 mon ths after the end of treatment. Acidification led to a decrease of the soil pH from 5.0 to 4.0 in the upper 2 cm of soil. The active fungal biomass, measured as the ergosterol content of the soil, increased. Af ter the end of the acid treatment pH differences decreased between plo ts. The active fungal biomass was lower, but the amount of total funga l hyphae was higher at the acid treated plots. Additionally, precipita tion of acid mist led to an acceleration of fine root and mycorrhizal development and their senescence. A total of 79 nematode species were found in the plots. Acidification caused a distinct decrease in specie s number, especially among K-strategists like omnivores and predators. The population density was not altered, but the dominance and abundan ce structure of the community changed. Acrobeloides nanus, Metateratoc ephalus crassidens and Aphelenchoides spp. spp. showed a higher freque ncy at the acidified plots. Others, like Cervidellus serratus, Filench us spp. or Aporcelaimellus obtusicaudatus, decreased. Among the trophi c groups, the occurrence of omnivore and predatory nematodes was affec ted negatively by acidification. The proportion of fungal feeding nema todes increased under acid precipitation, but the effect did not last after the end of the treatment. This corresponds to the amount of the active fungal biomass measured in the soil, indicating that the compos ition of the nematode fauna is changing with the presence or absence o f their food source.