Effects of long-term nutrient fertilisation and irrigation on the microarthropod community in a boreal Norway spruce stand

Intensive nutrient fertilisation of forests has been suggested as a method to increase production of biofuels as a replacement for fossil fuels. We used a field experiment in a Norway spruce, Picea abies (L.) Karst., stand in northern Sweden to examine possible long-term effects of forest fertilisation on soil fauna (Oribatida, Mesostigmata, Collembola, predatory macroarthropods). Fertilisers had been applied annually for a period of 13 years, both in solid and liquid form, and N was added as ammonium nitrate (75–100 kg N ha^-1 per year). For comparison, control plots and plots receiving only irrigation were included. An autumn sampling showed soil fauna decreases in plots receiving fertiliser in solid form, but increases in plots receiving liquid fertiliser. Clear shifts in community composition following both fertilisation methods were seen in Oribatida and Collembola, but species number and diversity were not significantly affected. This was probably due to increases in tolerant species that balanced decreases in other species. Liquid fertilisation had less negative effects on many species than fertilisation in solid form. Irrigation alone did not affect faunal abundances and had no effect on community composition of Oribatida and Collembola. The study indicates that intensive forest fertilisation will cause large shifts in soil microarthropod communities, but that species richness may remain unaffected. The risk of species loss will probably depend upon the size of the areas used for this purpose.