Century-long recovery of mycorrhizal interactions in European beech forests after mining

Ecological restoration strategies are emerging globally to counteract
biodiversity loss and ecosystem degradation. However, restored ecosystems
may not reach undisturbed biodiversity and functionality. One reason of
this limited success may be a focus on short-term recovery of diversity,
composition, or isolated functions. These simplified metrics may
underestimate the real time ecosystems need to recover. Thus, studies of
more complex metrics, like biotic interactions, at larger timescales, are
essential to understand ecosystem recovery. Using molecular
identification, we assessed the recovery of the interactions between
ectomycorrhizal (EcM) fungi and European beech (Fagus sylvatica L.) in two
opencast iron mines in use since the fourteenth century and abandoned over
107 and 148 years. Species richness, species diversity,
Basidiomycota/Ascomycota abundance ratio and taxonomic distinctness of EcM
fungi recovered to undisturbed values, whereas species composition was
still different. Certain fungal functional traits (i.e. exploration and
sporocarp types) also reached undisturbed values. Differences in soil pH
and NH4+ affected the composition of the EcM communities associated with
beech, suggesting that mining caused a long-term impact in soil
biogeochemistry, that directly impacted beech-EcM interactions. 
Mycorrhizal interactions require more than 150 years to recover following
mining. Contrary to the rapid recovery response provided by simple metrics
like species richness, recovery metrics with more ecological information,
like the identity of plant-EcM interactions, may be still capturing
signals of incomplete recovery.