Elevational patterns of fungal functional groups
All functional groups exhibited significant (p < 0.05)
differences in community composition among the three elevational forest
types in all geographic regions, consistent with our general Hypothesis
2. GNMDS plots of the datasets corresponding to functional groups showed
similar correlations with elevation and edaphic variables as detailed
above. The GNMDS ordinations of the four largest functional groups in
terms of OTU richness are shown in Fig. 2, with richness of taxonomic
orders displayed as vectors. In all regions, forest type was a
significant source of variation in community composition in almost all
functional groups, explaining ca. 20% of the variation in all fungi and
between 11.5% and 26.5% in the functional groups in Argentina, between
15.3% and 32.6% in Borneo, and between 13.0% and 31.5% in Panama
(Table 1). We did not find support for greater community turnover among
elevational forest types in plant-associated than in
non-plant-associated functional groups, in contrast to Hypothesis 2a.
Differences in richness among elevational forest types also were
observed in all functional groups in at least one region. Total fungal
richness was generally similar in all three elevational forest types,
except in Panama, where lower montane forests harbored significantly
more fungal OTUs than the other forest types (Fig. 3). We found three
functional groups, all associated with plants (ECM fungi, plant
pathogens, and wood decomposers), for which observed OTU richness as
well as proportional richness differed significantly among elevational
forest types in all three regions (Fig. 3, Fig. S5). Root-associated
fungi, the only remaining plant-associated guild, and animal pathogens,
differed significantly in richness in two regions, while richness of
mycoparasites and generalist saprotrophs generally did not differ
meaningfully among the elevational forest types. Greater differences
among vegetation types in plant-associated fungi compared to
non-plant-associated guilds are consistent with Hypothesis 2a.
Observed richness and proportional richness of plant pathogens and wood
decomposers, and, to a lesser extent, animal pathogens and generalist
saprotrophs, tended to be higher in lowland and/or lower montane forests
than in upper montane forests, largely consistent with Hypothesis 2b. In
contrast, ECM fungi, mycoparasites, and non-ECM root-associated fungi
showed mixed patterns (Fig. 3, Fig. S5). For example, in Neotropical
forests, ECM fungi peaked in richness in the upper montane forests, but
they were most diverse in the lower montane forests in Borneo. Similar
patterns also were observed with respect to proportional richness and to
some extent in proportional abundance, with the notable exceptions of a
pronounced abundance peak of mycoparasitic fungi and the abundance
minimum of saprotrophs in the lower montane forest in Borneo, and the
lack of significant differences in the proportional abundance of wood
decomposers among elevation zones in all three regions (Fig. S6).