Indications for the tracking of elevated nitrogen levels through the fungal route in a soil food web.

The objective of the present study was to determine the effects of elevated N in dead organic matter on the growth of fungi and to establish the consequences for the development of microbivores. Therefore, three fungal species were cultured on Scots pine litter differing in N content. The growth of the soil fungal species Trichoderma koningii, Penicillium glabrum and Cladosporium cladosporioides was directly influenced by the N content (ranging from 1.25 to 2.19% N) of the substrate. For all three fungal species maximum growth was highest at intermediate N content (1.55%) of the substrate. The fungivorous collembolan Orchesella cincta reached highest asymptotic body mass when fed with C. cladosporioides, grown on litter medium with intermediate N content (1.55%). The growth of O. cincta was lower when fed with C. cladosporioides from litter medium with the highest N content (2.19%). Similar results were obtained in mesocosm experiments in which pine litter with three levels of N (1.11, 1.78, 2.03% N) was used as substrate for the fungi. On litter with the highest N content (2.03%) hyphal length and asymptotic body mass of O. cincta were reduced. The results show that the N content of the substrate determines the growth of both fungi and fungivores, and suggest that elevated levels of N in soil track through the fungal part of the soil food web