In addition to driving global biogeochemical processes, soil microbial communities are responsible for an array of specialised functions that are critical to natural ecosystem health and preservation, such as detoxification and pollutant degradation following anthropogenic disturbance. While functional redundancy has long been assumed in global processes mediated by microbes, the degree to which anticipated biodiversity loss might affect such specialised capabilities is largely unknown. In this study, we addressed the microbial biodiversity and specialised function relationship by examining the response of two soils, similar in pedogenic attributes but naturally harbouring contrasting microbial diversity (low and high), to pollution (pyrene) stress, with or without plant and nutrient manipulation. We found that initial microbial composition and diversity were strongly correlated with soil native biodegradation potential, with high diversity soil showing biodegradation rates 3 times higher than the low diversity soil. Nutrient manipulation (organic and inorganic fertilisers) had mixed effects on the biodegradation rate, whereby both organic and inorganic amendments consistently improved the degradation rate in the low diversity soil, and had negative (inorganic fertiliser) to neutral (organic fertilisers) effect in soil with higher microbial diversity. Interestingly, and at odds with our predictions, plant presence did not substantially improve the pyrene degradation rate in any of the treatment combinations, indicating that, in this system, the level of microbial biodiversity has a prominent role in driving biodegradation. Taken together, our results suggest that initial microbial biodiversity should be taken into consideration when designing management strategies for rehabilitating natural systems disturbed by anthropogenic activities.

While over 70% of Australia is arid or dry, and most of the continent has phosphorus-deficient soil, much remains unknown regarding the evolution of photosynthetic systems in Australian species. Equally little is known regarding the potential adaptive strategies of Australian plants under future climate change scenarios. While soil nutrients can influence rates of photosynthesis, more empirical work is needed to understand how soil and climate jointly influence this process. Recent theoretical advances (“least-cost theory”) now allow us to generate testable hypotheses, e.g. that plants can reduce water costs associated with photosynthesis by investing more heavily in nitrogen-rich enzymes, or by reducing the enzymatic costs of photosynthesis by operating at a higher transpiration rate. Using this simple principle, we can predict how plants under different climates should vary in their relative dependence on water and soil nutrients. By merging existing datasets with field campaigns, we amassed a dataset that includes 60 sites and >500 woody and nonwoody species, occurring over a range of soil (pH, total phosphorus) and climate (rainfall, temperature, solar radiation) conditions. There was strong evidence in support of least-cost theory; compared to plants in phosphorus-deficient sites, plants in phosphorus-rich sites expressed a higher carboxylation capacity coupled with a lower transpiration rate (reducing water costs associated with photosynthesis when soil nutrients are abundant), and we found similar patterns in response to temperature and rainfall. These results suggest that the Australian flora have adapted their photosynthetic physiology to simultaneously tolerate dry and nutrient poor conditions at the continental scale.

Soil bacteria and fungi are key components of terrestrial ecosystems. They cycle nutrients essential to plant productivity and promote soil formation and structure. Increasing our knowledge of how natural and anthropogenic disturbances impact these soil communities is integral to our understanding of above ground ecosystem functioning and effective resource management. Fire is an important disturbance for the regeneration of both natural and managed eucalypt forests. Many studies have addressed the impacts of this disturbance on vegetation dynamics and soil chemistry, yet how the soil microbiome is affected is poorly understood.
We sampled soils from managed forests one month after logging and burning and quantified the diversity and abundance of soil bacterial and fungal communities across a fire severity gradient. Utilising next-generation sequencing and real-time quantitative PCR of bacterial and fungal specific genes we demonstrate that i) logging and high-intensity burning substantially reduces the biomass and diversity of soil bacteria and fungi, ii) fire severity is a strong driver of soil microbial community composition, iii) bacteria dominate soils disturbed by logging and fire and iv) the impacts of logging and fire on soil microbial communities are largely restricted to the top 10cm of soil. Our research suggests that low intensity burns are important for maintaining the diversity and abundance of soil microbial communities. Understanding both how these communities recover over time and their relationship with the regenerating vegetation is critical for establishing the link between above ground and below ground ecology.

Seed fungal endophytes (SFE) exist cryptically within the seed of their host plant and are thought to comprise much of the undescribed fungal diversity within ecosystems. SFE have been associated with seed-soil interactions, promoting successful seedling establishment and survival. However, major knowledge gaps exist regarding the diversity of SFE within natural ecosystems of Australia and the ecological filters that structure them. Using isolation techniques, Sanger sequencing of multiple loci and phylogenetic analysis, we characterised the culturable fungal endophyte community isolated from the seeds of two co-occurring Banksia species, (Banksia serrata and B. ericifolia) at four heathland sites in New South Wales, Australia. We investigated whether host or site ‘filters’ influenced the diversity, composition and connectivity of these communities. Fifty-nine Operational Taxonomic Units (OTUs) were identified, representing four fungal phyla, with latent saprophytes and latent pathogens being the dominant functional guilds present. Findings suggested that both host and site filters play a role in influencing SFE communities, with the host playing potentially a more important role. Co-occurrence network analyses revealed that communities differed in connectivity and the type of interactions occurring between SFEs. These findings contribute to our understanding of the breadth of ‘hidden’ diversity within natural ecosystems and the factors that structure them, with management implications for ecosystem conservation and restoration.

Forested ecosystems cover 30% of the world’s surface, providing valuable habitat for wildlife and supporting diversity. However, forests are vulnerable to a range of biotic and abiotic stressors including drought. Recently it has been shown that shrub encroachment can act synergistically with drought to cause the decline of overstorey trees. Coast banksia decline at Wilson’s Promontory National Park has been well documented since the 1970’s, yet no single cause has been found. Coast banksias are foundational species in the grassy woodlands at Wilson’s Prom, providing hollows for nesting sites and floral resources for native wildlife. The coastal grassy woodlands have been subjected to large scale shrub encroachment by coast tea-tree. This study investigated the decline of coast banksia trees due to shrub encroachment. We hypothesised that coast banksia can access groundwater resources, that the presence of a shrub layer limits water availability for coast banksia individuals and that there is a negative relationship between water stress of individuals when surrounded by a dense shrub understorey. In a glasshouse experiment we found that coast banksia have a dimorphic rooting system that enables them to access groundwater resources. Our natural experiments found that encroachment limits water availability for coast banksia, especially at depth, and that coast banksia individuals surrounded by shrubs had a higher degree of water stress compared to unencroached banksias. Our results indicate that water stress of shrub encroached coast banksia could lead to lower productivity and that shrub encroachment is contributing to the decline of coast banksia across WPNP.

Fine root endophytes (FRE) belong within the subphylum Mucoromycotina and are distinct from glomeromycotinian arbuscular mycorrhizal fungi (GAMF). Yet, they have been historically grouped within Glomeromycotina, given their arbuscule-forming capacity. Fine root endophytes and GAMF share nutrient exchange processes and arbuscule-senescing patterns with their hosts, suggesting that FRE functionally act as arbuscular mycorrhizal fungi. However, very little is known about their ecology. In this study, we aimed to understand the extent to which FRE and GAMF communities share ecological distributions and responses to environmental variables across large-scale environmental gradients. Trifolium subterraneum was used as a model species because it exists throughout southern Australia, allowing us to capture significant environmental gradients, while removing host variability. Soils and live plants were collected from 53 pastures across a very diverse range of soil types and rainfall zones. From roots, FRE and GAMF root colonisation was recorded, DNA extracted, and the 18S rRNA region was sequenced. The soil samples were analysed for their nutrient concentration. Our results show that FRE are much more diverse than previously thought but still less diverse than GAMF. Community composition of both groups was mainly driven by pH, rainfall, and aluminium. FRE richness increased with rainfall, while GAMF richness decreased. Finally, soil phosphorus had a negative effect on both FRE and GAMF root colonisation, supporting the idea that FRE belong to the functional group of arbuscular mycorrhizal fungi, while still having a distinct ecological niche from GAMF.

As the global population continues to increase, we face the formidable challenges associated with global climate change and the pressing need to produce more food in an ecologically sustainable way. Most plants, including the world’s most important crops, form associations with a co-evolved group of soil-dwelling fungi (Glomeromycotina) known as arbuscular mycorrhizal (AM) fungi. These fungi are not only important for plant productivity and nutrient acquisition but are critical to many ecosystem processes. Thus, the management of the AM symbiosis is likely to be critical to sustainable land management into the future. Yet, the outcomes of this symbiosis for the host plant can depend on the plant and fungal identities, for example C₄ plants are often observed to benefit more from AM fungi than C₃. It can also depend on environmental context, such as soil phosphorus availability.

Controlled-environment experimentation using different AM fungal inoculants reveals that increasing AM fungal species richness in the soil can have substantial positive growth and nutritional outcomes for major C₃ and C₄ crop species. However, the results also highlight that some plants may derive little or no benefit from increasing AM fungal species richness. These findings suggest that although it may not be uniformly advantageous to all plants, promoting AM fungal diversity in the soil is likely to be a key contributor towards agricultural sustainability.