Woodland ectomycorrhizal fungi benefit from large-scale reduction of nitrogen deposition in the Netherlands

1.Woodland ectomycorrhizal (ECM) fungal species declined considerably in the Netherlands in the late 20th century, mainly due to raised levels of atmospheric nitrogen deposition. Environmental measures have been taken to reduce this deposition, but it remains unclear whether and to what extent ECM species have benefitted from this.

2.We hypothesised that ECM species, especially those species that are known to be nitrophobic, i.e. sensitive to nitrogen loading, have recovered to some extent from the reduction in nitrogen deposition after 1994. We further hypothesised that, due to legacy effects of deposition, recovery has been stronger in regions where deposition levels have previously been lower.

3.To test these hypotheses, we analysed long-term opportunistic data, i.e., observations collected without standardised field method. We applied data filtering and a modified List Length method to adjust for potential biases in these data. The removal of bias left us with two periods to e...