Data from: Ectomycorrhizal fungi are more sensitive to high soil nitrogen levels in forests exposed to nitrogen deposition

Ectomycorrhizal fungi are essential for nitrogen cycling in many temperate
forests and responsive to anthropogenic nitrogen addition, which
generally, decreases host carbon allocation to the fungi. In the boreal
region, however, ectomycorrhizal fungal biomass has been found to
correlate positively with soil nitrogen availability. Still, responses to
anthropogenic input, for instance through atmospheric deposition, are
commonly negative. To elucidate whether variation in nitrogen supply
affects ectomycorrhizal fungi differently depending on geographical
context, we investigated ectomycorrhizal fungal communities along two
fertility gradients across nemo-boreal forests with similar ranges in soil
N/C ratios and inorganic nitrogen availability but located in regions with
contrasting rates of nitrogen deposition. Ectomycorrhizal biomass and
community composition remained relatively stable across the
nitrogen-gradient with low atmospheric nitrogen deposition, but biomass
decreased, and the community changed more drastically, with increasing
nitrogen availability in the gradient subjected to higher rates of
nitrogen deposition. Moreover, potential activities of enzymes involved in
ectomycorrhizal mobilisation of organic nitrogen decreased as N/C ratios
increased. In forests with low external input, we propose that stabilising
feedbacks in tree-fungal interactions maintain ectomycorrhizal fungal
biomass and communities even in highly fertile soils. In contrast,
anthropogenic nitrogen input seems to impair ectomycorrhizal functions.