Bioturbation by echidna (Tachyglossus aculeatus) in a forest habitat, south-western Australia

Bioturbation by digging animals is important for key forest ecosystem processes such as soil turnover, decomposition, nutrient cycling, water infiltration, seedling recruitment, and fungal dispersal. Despite their widespread geographic range, little is known about the role of the short-beaked echidna (Tachyglossus aculeatus) in forest ecosystems. We measured the density and size of echidna diggings in the Northern Jarrah Forest, south-western Australia, to quantify the contribution echidna make to soil turnover. We recorded an overall density of 298 echidna diggings per hectare, 21% of which were estimated to be less than 1 month old. The average size of digs was 50 ± 25 mm in depth and 160 ± 61 mm in length. After taking into account seasonal digging rates, we estimated that echidnas turn over 1.23 tonnes of soil ha−1 year−1 in this forest, representing an important role in ecosystem dynamics. Our work contributes to the growing body of evidence quantifying the role of these digging animals as critical ecosystem engineers. Given that the echidna is the only Australian digging mammal not severely impacted by population decline or range reduction, its functional contribution to health and resilience of forest ecosystems is increasingly important due to the functional loss of most Australian digging mammals

Forest die-off following global-change-type drought alters rhizosphere fungal communities

Globally, forest die-off from global-change-type drought events (hotter droughts) are of increasing concern, with effects reported from every forested continent. While implications of global-change-type drought events have been explored for above-ground vegetation, below-ground organisms have received less attention, despite their essential contributions to plant growth, survival, and ecosystem function. We investigated rhizosphere fungal communities in soils beneath trees affected by a global-change-type drought in a Mediterranean climate-type ecosystem in southwestern Australia, quantifying how fungal richness, composition and functional groups varied along a drought impact gradient. Following a forest die-off three years previously, we collected soils beneath dead and alive trees within forest exhibiting high, minimal and relatively unaffected levels of forest die-off. Rhizosphere fungal DNA was extracted from soils, amplified and subjected to high throughput sequencing. Fungal community composition varied significantly (P < 0.001) along the drought impact gradient with less richness in drought affected stands. There was some evidence of community differentiation between dead versus alive trees (P = 0.09), and no difference in rarefied richness and diversity. When considered by functional group, die-off-impacted plots had more arbuscular mycorrhizal fungi (AM) and saprotrophs, and fewer ectomycorrhizal fungi (ECM), compared with living trees from the unaffected plots. Further, within die-off plots, dead versus alive tree rhizosphere samples contained more AM, saprotrophs and pathogens, and fewer ECM. Disruptions to rhizosphere fungal communities, such as altered functional groups, can have implications for ecosystem persistence and function, particularly in regions projected to experience increased global-change-type drought events

Habitat fragmentation in a Mediterranean-type forest alters resident and propagule mycorrhizal fungal communities

Aims Anthropogenic activities disturb forests and their associated mycorrhizal fungi. The combination of climate change and habitat fragmentation are linked to increased incidence of a canker disease in a Mediterranean-type forest tree in Western Australia. As changes in communities of mycorrhizal fungi could predispose these Mediterranean-type forest trees to decline, we investigated how two aspects of mycorrhizal fungal community structure, soil propagules and resident communities on mature trees, respond to habitat fragmentation. Methods Roots were collected from a forest tree (Corymbia calophylla) across a disturbance gradient. Soil collected from the same disturbance gradient was used in a glasshouse bioassay with C. calophylla as the bioassay host (i.e., soil propagule community). After four months, we harvested the seedlings and collected roots. DNA was extracted from the field roots (resident community) and glasshouse roots (propagule community), amplified with fungal specific primers, labelled with specific barcodes and subjected to 454 pyrosequencing. Results Mycorrhizal fungal community composition overlapped substantially between the soil propagule and resident communities. However, the resident community had greater mycorrhizal fungal richness than the soil propagule community. Habitat fragmentation had a similar effect on each community structure: communities along highly fragmented areas had different community compositions than communities in a healthy forest. Conclusion With the increased mortality of C. calophylla forest trees in recent years along edge habitats, understanding the effects habitat fragmentation has on communities of mycorrhizal fungi will further elucidate host-mutualist interactions in these forest ecosystems. The changes in community composition of mycorrhizal fungal species in both propagule and resident pools can have cascading effects on future tree establishment and health by predisposing forest trees to other abiotic or biotic factors

The tripartite relationship between a bioturbator, mycorrhizal fungi, and a key Mediterranean forest tree

Mycorrhizal fungi serve important functions in Australian ecosystems by forming mutualistic symbioses with plants that facilitate water and nutrient uptake. Scat analyses have shown that southern brown bandicoots (Isoodon obesulus fusciventer; 'Quenda') regularly feed on fungi, including ectomycorrhizal (ECM) species. Many of these ECM species are hypogeous and rely on mycophagous animals such as quenda to disperse their spores. We explored the tripartite relationship between a keystone Mediterranean tree, its associated mycorrhizal fungi, and a mammalian disperser. Wild-collected quenda scats were used as a mycorrhizal inoculum to grow Eucalyptus gomphocephala from seeds under glasshouse conditions. Autoclaved scats were used as a negative-control and sporocarp tissue from Pisolithus and Scleroderma ectomycorrhizal species were mixed together as a positive-control inoculum. Seedlings were harvested at 10 weeks to assess seedling growth and early mycorrhizal colonization of roots by high-throughput DNA sequencing. Quenda scat successfully introduced fungi to seedlings, shown by a 56% overlap of fungal operational taxonomic units (OTUs) detected in the scats and roots grown in fresh scat inoculum. Scat-inoculated seedlings had richer root mycorrhiza fungal assemblages and a higher proportion of mycorrhizal taxa compared to negative- and positive-controls. However, no difference in shoot or root mass in these young seedlings could be attributed to root fungi assemblages at this early growth stage, possibly reflecting that the role of mycorrhizae in these early seedlings was parasitic, rather than facilitatory. Our study has shown that spores of mycorrhizal fungi from the quenda scat inoculum can successfully germinate and colonize seedling roots after passage through the quenda gut

Disease development of Dothistroma needle blight in seedlings of Pinus sylvestris and Pinus contorta under Nordic conditions

Dothistroma needle blight (DNB), caused by Dothistroma septosporum, was observed for the first time in the Nordic countries during the 21st century, and the dynamics of the disease under Nordic conditions are still poorly explored. In this study, we followed the development of DNB on seedlings of Pinus sylvestris and Pinus contorta, planted at two forest sites in central Sweden. PCR with species-specific primers was used to detect infections of D. septosporum in needle samples collected over a two-year period. The seedlings were also examined for typical red bands and fruit bodies (conidiomata). One-year-old needles that were present on the seedlings at the time of planting became infected during the first summer. The first conidiomata appeared on P. sylvestris in autumn the same year and on P. contorta in spring the following year. The first infections of the current-year needles of both host species occurred in summer, as they were starting to elongate, and the following spring the first conidiomata appeared. On one of the sites, many seedlings carried latent infections without any symptom development. At some time points, infections of D. septosporum were detected in more than 50% of the seedlings, but red bands and conidiomata were only observed on a small number of the seedlings throughout the study period. No clear difference was observed in the susceptibility of infection between the two host species; nonetheless, at the same site, the mortality of P. sylvestris was higher than that of P. contorta, and this is likely primarily due to other stresses and the presence of another needle pathogen, Lophodermium seditiosum

Digging mammals contribute to rhizosphere fungal community composition and seedling growth

Bioturbation is an important ecosystem process, and the loss of native digging mammals due to introduced predators and habitat loss may have detrimental consequences for ecosystem health. The mycophagous woylie (Bettongia penicillata ogilbyi) was once widespread across the Australian continent and currently exists in a greatly reduced range, while the omnivorous quenda (Isoodon fusciventer), which once occurred across the southern part of Western Australia (WA), remains common in south west WA over a reduced range. Populations of these two digging marsupials are currently maintained within sanctuaries where they can reach high densities. To assess the influence these digging marsupials have on fungal assemblages, we investigated fungal root associations among seedlings of a key mycorrhizal forest canopy species, Corymbia calophylla, R. Br. K. D. Hill and L. A. S. Johnson. Seedlings were grown in soil collected from inside (heavily-dug soil) and outside (minimally-dug soil) two predator-proof sanctuaries. Our results showed that above-ground seedling biomass was significantly greater for seedlings grown in soil collected from inside the sanctuaries. There were no differences in the diversity or species richness of rhizosphere fungal communities isolated from these seedlings; however, the community composition was significantly different. This was most obvious for the predator-proof enclosure that had been in place for 20 years (Karakamia Sanctuary) compared with the more recently-installed Perup Sanctuary (fenced in 2010; 4 years before this study). At Karakamia, there were greater numbers of putatively hypogeous ectomycorrhizal fungi inside the enclosure and four times the number of operational taxonomic units of arbuscular mycorrhizal fungi outside the enclosure. The differences in fungal communities suggest that digging mammals play a pivotal role in ecosystem functioning by influencing the rhizosphere of this key forest canopy species, which has implications for maintaining the health and persistence of forests

Potassium amendment increases biomass and reduces heavy metal concentrations in Lablab purpureus after phosphate mining

Agricultural pursuits in post‐mining environments are becoming increasingly important globally as many regions are challenged with food insecurity and post‐mining land‐use legacies. Although there are many advantages for agricultural production at post‐mining sites, these substrates have abiotic and biotic challenges for plant growth, including poor fertility, heavy metals, and lack of beneficial soil microbes. We investigated whether increased potassium (K) levels in a post‐phosphate mining substrate on Christmas Island, Australia, could improve plant productivity and reduce heavy metal concentrations. Addition of K (80 and 160 kg ha−1) significantly increased plant biomass and enhanced root growth and mycorrhizal fungal colonisation rates. Potassium amendment was also strongly correlated with lower heavy metal concentrations in leaf material. Clearly, K is the critical limiting nutrient for legumes in post‐phosphate mining sites on Christmas Island for enhancing biomass and health. We hypothesise that heavy metals were either being diluted in a larger biomass and/or healthy plants could also select against heavy metal uptake; however, this requires further investigation of the mechanisms involved. These results have significant global ramifications for sites transitioning from mining to agriculture

Reducing the risk of invasive forest pests and pathogens: Combining legislation, targeted management and public awareness

Intensifying global trade will result in increased numbers of plant pest and pathogen species inadvertently being transported along with cargo. This paper examines current mechanisms for prevention and management of potential introductions of forest insect pests and pathogens in the European Union (EU). Current European legislation has not been found sufficient in preventing invasion, establishment and spread of pest and pathogen species within the EU. Costs associated with future invasions are difficult to estimate but past invasions have led to negative economic impacts in the invaded country. The challenge is combining free trade and free movement of products (within the EU) with protection against invasive pests and pathogens. Public awareness may mobilise the public for prevention and detection of potential invasions and, simultaneously, increase support for eradication and control measures. We recommend focus on commodities in addition to pathways, an approach within the EU using a centralised response unit and, critically, to engage the general public in the battle against establishment and spread of these harmful pests and pathogens

Urban remnant size alters fungal functional groups dispersed by a digging mammal

Digging animals perform many ecosystem functions, including soil turnover and vectoring fungi, particularly mycorrhizal fungi. However, these animals are also susceptible to the impacts of urbanisation, resulting in altered ecosystem processes. Some digging mammals, such as the omnivorous quenda (Isoodon fusciventer), a medium-sized marsupial bandicoot endemic to southwestern Australia, persist in urban landscapes and may play important roles as fungal vectors. This paper examines the fungal community in quenda scats from natural vegetation remnants within a fragmented urban landscape to ask: are quenda acting as vectors for a functionally diverse fungal community?; what fungal functional types are being vectored?; and does remnant size impact fungal species richness and composition vectored by quenda? We sequenced 53 scat samples collected from remnants and found that quenda disperse a functionally diverse fungal community, with 31% of the molecular operational taxonomic units (OTUs) putatively mycorrhizal. Fungal OTU richness was greatest in scats from smaller remnants due to higher mean relative abundance of saprotrophs, pathogens and yeasts. Fungal OTU richness of ectomycorrhizal fungi, critical for plant growth, were found at a higher abundance in larger remnants. Fungal composition was affected by remnant size, type and condition of vegetation, and soil type. Our results indicate that maintaining digging mammal populations within urban landscapes may assist with dispersal of fungi that facilitate fungal-plant interactions, contributing to ecosystem health. These results are important to understand the complex ecological implications of urbanisation, and how remaining mammals are critical in maintaining ecosystem processes within the urban land-use matrix