Pantropical core mycobiome of lowland and montane forests
The rarefied, combined dataset included 7612 OTUs. Of these, only 211
OTUs were shared among all three regions. The majority of OTUs were
restricted to one geographic region, but 376 were shared between the two
Neotropical regions, 188 were shared between the Yungas and Borneo, and
192 were shared between Borneo and Panama (Fig. 4). These findings are
consistent with Hypothesis 3, i.e., little overlap among species pools
of the three biogeographic regions, with more shared species between the
two Neotropical regions.
Both abiotic environmental variables and geographic location were
strongly correlated with fungal community structure in separate Mantel
tests (r = 0.658 and r = 0.497, respectively; all p< 0.001), and when they were combined in partial Mantel tests,
resulting in significant correlation of environmental factors with
fungal community structure when location was accounted for (r =
0.553, p < 0.001), and vice versa (r =
0.279, p < 0.001). PerMANOVA indicated that geographic
region and forest type explained 7.3% and 5.8% of the variation in
community composition, respectively, while among abiotic variables, MAP
explained 7.4%, pH 6.9%, and MAT 5.7% of the variation, all with
significant contributions in the combined model, consistent with
Hypothesis 1.
Of 360 fungal OTUs with significant (p < 0.05)
indicator value for a forest type, 136 occurred both in the Neo- and
Paleotropics and were included in the pantropical comparison. Of these,
40, 24, and 72 were indicators for the lowland, lower montane, and upper
montane forests, respectively (Table S2).
Discussion
Fungal biodiversity in tropical forests remains little known, and
opportunities to compare data from similar guilds across diverse
tropical forest types at local and global scales are rare. The deep
sequence data presented here show that composition of the total fungal
community, as well as that of all functional groups, is strongly
structured according to elevational forest types in both the Neo- and
the Paleotropics. Contrary to vascular plants, where the lowland and the
lower montane forests typically harbor more species than upper montane
forests (Aiba and Kitayama 1999; Brown et al. 2001; McCain and
Grytnes 2010), we did not find substantial differences in soil fungal
richness among the three elevational zones in Argentina and Borneo. The
lack of a strong elevational pattern in fungal richness is similar to
the lack of latitudinal differences in fungal richness on a global scale
(Větrovský et al. 2019). Panama was an exception, where the
mid-elevation peak in fungal richness is concordant with vascular plant
richness in Central American mountains (Cardelús et al. 2006,
Prada et al. 2017). However, in all functional groups and in all
regions, compositional structure appears to be driven by elevation and
the resulting environmental filtering according to contrasting climatic
and edaphic conditions, and to a smaller extent, differences in
vegetation. Furthermore, composition of fungal communities in the lower
montane forests may be regarded as intermediate between communities of
the lowland and upper montane forests, although, as the other two forest
types, the lower montane forest also possesses several characteristic
taxa.