Habitat filtering in soil food webs
As anticipated, habitat filtering strongly influenced soil food web
structure (Crotty et al. 2014; Arribas et al. 2021; Seppet al. 2021). Differences in abiotic conditions and resource
availability between habitats could explain the observed differences in
the proportions of trophic groups. Grassland soils exhibit lower
acidity, higher P and N availability and a lower C/N ratio (Joimelet al. 2016, Fig.S5), and have a higher below-ground plant
biomass, which is more easily decomposed, leading to significant inputs
of readily decomposable organic matter into the soil (Mason & Zanner
2005; Heděnec et al. 2022). These factors likely enhanced
resource availability for detritus-based trophic groups, resulting in
the higher dominance of copiotroph decomposers (e.g., saprophytic fungi
and bacteria), micro- or meso- detritivores (i.e., Enchytraeidae) and
microbivores in grasslands. In contrast, plant detritus in forests,
which is more challenging to decompose, serves as a direct resource for
litter and wood saprotrophic fungi and provide a habitat for
macro-detritivores, which feed on plant litter and associated fungi
(David & Handa 2010; Zuo et al. 2014). Light availability in
grasslands may favour the presence of photoautotrophic bacteria that use
light as their primary resource, and facilitate interactions, such as
arbuscular mycorrhiza (Konvalinková & Jansa 2016). Moreover, grasslands
had a higher proportion of phytoparasites, likely due to the higher
biomass of fine roots in this habitat (Jackson et al. 1997;
Heděnec et al. 2022), which are more easy to colonise by
symbionts, while forests had a higher proportion of zooparasites,
benefiting from a greater abundance of potential hosts, predominantly
arthropods, molluscs or earthworms, for the taxa belonging to our
zooparasite groups. These findings align with our results showing that
trophic interactions within the soil food web contributed to explain
food web dissimilarities between habitats (Fig. 4) and are consistent
with previous studies examining changes in the trophic composition of
protists (de Araujo et al. 2018; Fiore-Donno et al. 2020)
and nematodes (Zhao & Neher 2014) across habitats. The distinct
identities of soil antagonists in the soil food webs from grassland to
forests warrant further investigation as they could provide insights for
land management strategies in mountain ecosystems (Wall et al.2015).