Anthropogenic disturbance impacts ectomycorrhizal communities and abiotic soil properties: implications for an endemic forest disease

In forest ecosystems, habitat fragmentation negatively impacts stand
structure and biodiversity; the resulting fragmented patches of forest
have distinct, disturbed edge habitats that experience different
environmental conditions than the interiors of the fragments. In southwest
Western Australia, there is a large-scale decline of the keystone tree
species Corymbia calophylla following fragmentation and land use change.
These changes have altered stand structure and increased their
susceptibility to an endemic fungal pathogen, Quambalaria coyrecup, which
causes chronic canker disease especially along disturbed forest habitats.
However, the impacts of fragmentation on belowground processes in this
system are not well understood. We examined the effects of fragmentation
on abiotic soil properties and ectomycorrhizal (ECM) and arbuscular
mycorrhizal fungal (AMF) communities, and whether these belowground
changes were drivers of disease incidence. We collected soil from 17 sites
across the distribution range of C. calophylla. Soils were collected
across a gradient from disturbed, diseased areas to undisturbed,
disease-free areas. We analysed soil nutrients and grew C. calophylla
plants as a bioassay host. Seedlings were harvested and roots collected
after six months of growth. DNA was extracted from the roots, amplified
using fungal specific primers and sequenced using Illumina MiSeq.
Concentrations of key soil nutrients such as nitrogen, phosphorus and
potassium were much higher along the disturbed, diseased edges in
comparison to undisturbed areas. Disturbance altered the community
composition of ECM and AMF; however, only ECM communities had lower
rarefied richness and diversity along the disturbed, diseased areas
compared to undisturbed areas. Accounting for effects of disturbance, ECM
diversity and leaf litter depth were highly correlated with increased
disease incidence in C. calophylla. In the face of global change,
increased virulence of an endemic pathogen has emerged in this
Mediterranean-type forest.