Spatial variations in ectomycorrhizal fungi and host tree reciprocal relations are associated with the local distribution patterns of Minjiang fir

Abstract

Ectomycorrhizal fungi (ECMF) can help maintain the natural range of host trees by assisting their occupancy in the boundary of distribution. However, it is unclear whether the boundary-dependent variations in ECMF communities and their relationships with hosts are associated with the patterns of local-scale host tree distributions. In this study, we investigated the community structure of ECMF in the root tips of the Minjiang fir (Abies fargesii var. faxoniana) saplings, and examined the variations in root-associated ECMF communities and their relationships with the fir saplings along environmental gradients from the centric suitable habitats (SH) on shady slopes to range boundaries (RB) at the upper and lower elevations of the SH and on sunny slopes. We found that both the SH and the upper RB were enriched by the ECMF taxa in the genus Cortinarius, which were positively correlated with the basal diameter (BD) of the firs. In contrast, the lower RB of the shady slopes and the sunny slopes harbored a higher abundance of the ECMF taxa in the genus Tylospora, which were negatively correlated with the BD of the firs. The relationships between the firs and some of the same ECMF species, such as Cortinarius balaustinus and Cortinarius casimiri, shifted from positive at the SH to negative at the lower RB of the shady slopes and on sunny slopes. Soil properties differed between habitat types, so do the relationships of soil properties with ECMF communities. These marginal alterations in ECMF communities and their relationships with the fir saplings were not explainable by changes in soils. Our study highlighted habitat-dependent shifts in root-associated ECMF communities and their correlations with Minjiang fir saplings from suitable habitats to range boundaries. The results suggest that these marginal patterns may be associated with variations in habitats rather than current soil properties for Minjiang firs. The spatial variations in ECMF communities and their relationships with fir saplings could be useful indicators for identification of the site suitability for Minjiang fir regeneration and conservation.