Environmental drivers
Abiotic environmental variables correlated with elevation to a varying
degree in the three sampled regions. As expected, MAT showed strong
negative correlation with elevation in all three regions. MAP generally
was not correlated with elevation except in Argentina, where it was
highest in the lower montane forest zone (Fig. S4). Soil pH tended to
decrease with elevation in all regions, although in Panama the trend was
not significant. In Borneo, pH increased again above 3500 masl,
representing the sparsely vegetated summit zone of Mt. Kinabalu. In a
related manner, soil organic material (OM), and to a lesser extent N,
were correlated positively with elevation in general, again with change
of trend in the summit zone of Mt. Kinabalu (Fig. S4).
GNMDS ordinations revealed strong structuring of fungal communities
according to elevation in all three regions (Pearson’s correlations
values: r 2 = 0.8633,r 2 = 0.9406, and r 2 =
0.9661; all p = 0.001) in Argentina, Borneo, and Panama,
respectively (Fig. 1). With respect to abiotic variables, MAT and soil
pH were correlated strongly with fungal community composition in all
three regions (all p = 0.001), whereas other climatic and edaphic
variables differed in their importance among the regions. Partial Mantel
tests indicated that abiotic environmental variables were linked
robustly to community structure in all sampling areas (Argentina:r = 0.636, p < 0.001; Borneo: r = 0.444,p < 0.001; Panama r = 0.576, p< 0.001), when spatial proximity was accounted for (control
matrix), whereas spatial proximity was not significant (all p ˃
0.1) when abiotic variables were controlled.
In the PerMANOVA analyses, MAT and pH tended to explain the greatest
variation in the total fungal community composition and remained
significant contributors in the combined model in all three regions when
correlation among parameters was accounted for. The contribution of
other abiotic variables varied among functional groups and geographic
regions, with P and OM explaining significant proportions of variation
in fungal community structure in at least two regions and MAP being
especially important in Argentina (Table 1). These results are
consistent with Hypothesis 1, particularly with respect to MAT, pH, and
to a lesser extent MAP, as drivers of soil fungal community composition.