Abstract:
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 (AM) fungal 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. Plants were harvested and roots collected after 6 months of growth.
DNA was extracted fromthe 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 AM
fungi; however, only ECM fungal communities had lower rarefied richness and diversity
along the disturbed, diseased areas compared to undisturbed areas. Accounting for
effects of disturbance, ECM fungal 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.
