The functional roles of psyllid abundance and assemblage on bird-associated forest defoliation.

Fluctuations in the abundance of insect herbivores and the severity of damage they cause to their hosts are key factors affecting tree health and trophic interactions. Bell miner associated dieback (BMAD) is a trophic cascade involving eucalypt trees, psyllids and bell miners. Bell miners are a territorial species of bird that reduce insectivorous bird diversity, thereby increasing psyllid abundances. The role of psyllids in BMAD is debated, primarily because psyllid host specificity, genus, defoliation potential and/or lerp composition have been conflated or unexplored. This study documented psyllid communities and canopy structure of four eucalypt hosts (Eucalyptus bridgesiana, E. caliginosa, E. propinqua and E. siderophloia) in BMAD and non-BMAD-affected forests in northern New South Wales. Psyllid abundances were significantly higher in BMAD-affected forests. However, psyllid assemblages did not differ between forest types which contrasts with an influential hypothesis concerning bell miner farming of psyllids that produce sugary lerps (Glycaspis species). Importantly, psyllid communities differed among species of eucalypt host. Hosts supporting higher abundances of Cardiaspina tended to have a stronger negative relationship between canopy health and psyllid abundances than other host trees. Cardiaspina were also found on older leaves and associated with more leaf damage than other psyllids. Unlike most other psyllid genera, Cardiaspina initiate premature foliar senescence leading to defoliation which ultimately changes the age structure of leaves of the canopies of affected trees. Our study supports the functional linkage between psyllid assemblages, their relative abundances and defoliation potential to bottom-up mechanisms behind a bird-associated trophic cascade.

An assessment of ectomycorrhizal fungal communities in Tasmanian temperate high-altitude Eucalyptus delegatensis forest reveals a dominance of the Cortinariaceae.

Fungal diversity of Australian eucalypt forests remains underexplored. We investigated the ectomycorrhizal (EcM) fungal community characteristics of declining temperate eucalypt forests in Tasmania. Within this context, we explored the diversity of EcM fungi of two forest types in the northern highlands in the east and west of the island. We hypothesised that EcM fungal community richness and composition would differ between forest type but that the Cortinariaceae would be the dominant family irrespective of forest type. We proposed that EcM richness would be greater in the wet sclerophyll forest than the dry sclerophyll forest type. Using both sporocarps and EcM fungi from root tips amplified by PCR and sequenced in the rDNA ITS region, 175 EcM operational taxonomic units were identified of which 97 belonged to the Cortinariaceae. The Cortinariaceae were the most diverse family, in both the above and below ground communities. Three distinct fungal assemblages occurred within the wet and dry sclerophyll forest types and two geographic regions that were studied, although this pattern did not remain when only the root tip data were analysed. EcM sporocarp richness was unusually higher than root tip richness and EcM richness did not significantly differ among forest types. The results are discussed in relation to the importance of the Cortinariaceae and the drivers of EcM fungal community composition within these forests.

Strong host preference of ectomycorrhizal fungi in a Tasmanian wet sclerophyll forest as revealed by DNA barcoding and taxon-specific primers.

Ectomycorrhizal (ECM) symbiosis is a widespread plant nutrition strategy in Australia, especially in semiarid regions. This study aims to determine the diversity, community structure and host preference of ECM fungi in a Tasmanian wet sclerophyll forest. Ectomycorrhizal fungi were identified based on anatomotyping and rDNA internal transcribed spacer (ITS)-large subunit (LSU) sequence analysis using taxon-specific primers. Host tree roots were identified based on root morphology and length differences of the chloroplast trnL region. A total of 123 species of ECM fungi were recovered from root tips of Eucalyptus regnans (Myrtaceae), Pomaderris apetala (Rhamnaceae) and Nothofagus cunninghamii (Nothofagaceae). The frequency of two thirds of the most common ECM fungi from several lineages was significantly influenced by host species. The lineages of Cortinarius, Tomentella-Thelephora, Russula-Lactarius, Clavulina, Descolea and Laccaria prevailed in the total community and their species richness and relative abundance did not differ by host species. This study demonstrates that strongly host-preferring, though not directly specific, ECM fungi may dominate the below-ground community. Apart from the richness of Descolea, Tulasnella and Helotiales and the lack of Suillus-Rhizopogon and Amphinema-Tylospora, the ECM fungal diversity and phylogenetic community structure is similar to that in the Holarctic realm.