Acid deposition in a spruce forest soil: Effects on nematodes, mycorrhizas and fungal biomass

The belowground biota (nematodes, fungal biomass, roots and mycorrhizal development) of a mature Sitka spruce stand under the influence of acid precipitation (equimolar sulphuric acid and ammonium nitrate) was investigated. Sampling took place after 3 years of treatment and 5 months 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. After the end of the acid treatment pH differences decreased between plots. The active fungal biomass was lower, but the amount of total fungal hyphae was higher at the acid treated plots. Additionally, precipitation 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 species number, especially among K-strategists like omnivores and predators. The population density was not altered, but the dominance and abundance structure of the community changed. Acrobeloides nanus, Metateratocephalus crassidens and Aphelenchoides spp. spp. showed a higher frequency at the acidified plots. Others, like Cervidellus serratus, Filenchus spp. or Aporcelaimellus obtusicaudatus, decreased. Among the trophic groups, the occurrence of omnivore and predatory nematodes was affected negatively by acidification. The proportion of fungal feeding nematodes 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 composition of the nematode fauna is changing with the presence or absence of their food source.