Soil propagule banks of ectomycorrhizal fungi along forest development stages after mining.

Ectomycorrhizal fungal (EMF) propagules play an important role in seedling establishment following disturbance. However, little is known about how the EMF propagule community changes with forest development. In this study, EMF propagules were examined using seedling bioassays in rhizosphere soils collected from a recently closed Pb-Zn tailing (Taolin Pb-Zn tailing (TLT)), a Cu tailing (Dexing Cu No. 2 tailing (DXT)) that had undergone 21 years of restoration, and a mature Masson pine (Pinus massoniana) forest (DXC) outside the Cu mining areas. The corresponding EMF communities colonizing Masson pine at each site were also investigated for comparison. After 8 months of running bioassays, ectomycorrhizal colonization was poor for seedlings grown in TLT (9.0 % ± 14.9 %) and DXT soils (22.4 % ± 17.7 %), while DXC seedlings were well colonized (47.5 % ± 24.9 %). Internal transcribed spacer sequencing revealed that EMF species richness increased with forest development in both the propagule bank (TLT, 6; DXT, 7; DXC, 12) and in the field (TLT, 8; DXT, 14; DXC, 26), though richness was lower in propagule banks. Several lineages, such as Cenococcum, Rhizopogon, Inocybe, Suillus, and Atheliaceae, were frequently encountered in propagule communities, but species assemblages were different among the three sites. Canonical correspondence analysis revealed that several soil parameters, i.e., N, EC, Cu, Pb, Zn, etc., were responsible for the distribution of EMF in the field and bioassay seedlings. The highest overlap in EMF species composition between the propagule bank and the field community was observed at the recently closed tailing (Morisita-Horn similarity = 0.71 for TLT), whereas the lowest overlap occurred at the mature forest (0.26 for DXC). These results indicate that EMF propagules in soil are less frequent and diverse in early primary succession and become more frequent and diverse along forest development, due mainly to the accumulation of dormant spores of Rhizopogon spp. and sclerotia of Cenococcum spp. Thus, EMF propagule communities in soil may diverge from those root-colonizing EMF communities along a gradient of forest development.