Richness and uniqueness of soil microarthropod communities
After denoising and chimera filtering, the removal of putative spurious
sequences by metamate, followed by additional filtering of
community tables, generated a fully-filtered dataset comprising 907 ASVs
which clustered into 386 OTUs (putative species) across the three
taxonomic groups. Specifically, we retrieved a total of 353 ASVs and 154
OTUs of Coleoptera, which was the most diverse group at both across- and
within-habitat scales. The Acari and Collembola datasets comprised 237
and 317 ASVs which clustered into 139 and 93 OTUs, respectively (Figure
2).
The average α diversity of haplotypes per sampling site differed among
habitat types, with the Cyprus cedar (Cb) habitat showing
significantly higher richness than the other four forest types (Tukey’s
test: p-value <0.028 in all comparisons involving Cb; Figure 2). At OTU level, the average α diversity per site was
higher in the forest types distributed at low and mid altitudes
(Pb, Qa and Cb) than in those habitats restricted
to higher elevations (Pn and Jn Figure 2). However, the
significance of this pattern was not preserved after post-hoc tests
(Tukey’s test: all p-values >0.123). When soil
substrates were independently compared, the leaf litter layer showed
significantly higher richness (α diversity) than the deep soil substrate
in all comparisons (Figure S2). The average local contribution to β
diversity (LCBD) per sampling site differed significantly among
habitats, with the Calabrian Pine (Pb) and Golden Oak (Qa)
communities showing significantly higher uniqueness at both ASV and OTU
level when compared to the high-altitude Pn and Jn communities (Tukey’s test: p-value <0.05 in most
comparisons involving Pb or Qa; Figure 2). When
independently analyzed, deep soil communities showed significantly
higher LCBD estimates, indicating a more unique composition than the
leaf litter communities (Figure S2, inset plots), a pattern particularly
evident in the high-altitude Pn and Jn communities (Figure
S2).
Regression analyses (GLMMs/GLMs; see Supplemental Information) showed a
significantly negative relationship between average richness (α
diversity) of ASVs per site and longitude (Lon), indicating that
community richness decreased towards the east of the Troodos mountain
range (Table 1; Table S4). To ensure that this relationship was not
biased by the Cyprus cedar (Cb) sites, which are geographically
restricted to the westernmost part of the study area and have the
highest ASV richness (Figures 1-2), additional analyses excluded these
sites. These analyses consistently supported the significant effect of
longitude on ASVs richness across forest habitats (95% CI:
[-34.968] - [-4.032]). Conversely, the richness (α diversity) of
OTUs per site was only explained by the topoclimatic predictor
ENVPC2 (Table 1; Table S4). Similarly, we found that
LCBD estimates at both ASV and OTU levels were significantly correlated
with the topoclimatic variables, as summarized with the
ENVPC1 and ENVPC2 predictors (Table 1;
Table S4).