We know surprisingly little about the distribution and functional capacities of plant roots - and consequently, about how plants access resources distributed throughout soil profiles. Current root trait frameworks are heavily shaped by temperate ecosystems, often under nitrogen-dominated soil dynamics. Fine root strategies have been summarized into a two-dimensional "root economic space" (RES) - primarily based on northern hemisphere data - with a conservation dimension expressed by high fine root tissue density, and a collaboration dimension expressed by fine root diameter.

We first examine what is known about these traits in the Australian flora and how they align or diverge from global patterns. Severe resource constraints both in terms of low phosphorus, low average nitrogen content, but also extremely variable rainfall have been suggested to make many of Australia’s ecosystems unique with some iconic Australian taxa such as Proteaceae potentially expanding the root functional trait space.

Second, the talk explores whether these root traits are linked to spatial deployment belowground and how we expect these relationships to shift with ontogeny. A working hypothesis is that root placement (deep vs shallow root investment) and construction (how they are built) have sufficiently different functions that they vary independently. On the other hand, we also expect that species optimise root investment according to expected resource returns in a given environment, leading to predictable developmental trajectories. Preliminary results from several Eucalyptus species comparing seedling root system expansion to adult rooting depth suggest they do. As belowground spatial deployment is challenging to measure in adult plants, identifying consistent trait trajectories during early development offers a promising approach. Investigating these ontogenetic patterns will improve our understanding of how plants explore and exploit belowground space.

Understanding the effects of fire on ecosystem function is critical for both above- and belowground processes. Mycorrhizal fungi play essential roles belowground, yet most studies rely on DNA-based methods that capture community composition but not functional attributes. Here, we assessed community responses alongside functional traits of mycorrhizal fungi, biomass, and hyphal chemistry using in-growth mesh bags. We studied 12 dry sclerophyll forest sites in the Sydney Basin, spanning gradients of historical fire frequency and fire severity from the most recent fire (the 2019/20 Black Summer fires). We evaluated direct effects of fire regime and indirect effects of soil nutrients using high-throughput DNA sequencing, joint species distribution modelling, and direct measurements of biomass and hyphal chemistry.

Mycorrhizal community composition was associated with fire frequency and severity but did not correspond to major functional changes. In contrast, nutrient availability, particularly soil orthophosphate, had limited effects on community composition but strongly influenced fungal function and biomass and altering hyphal stoichiometry. To our knowledge, this is the first study to measure mycorrhizal biomass and hyphal chemistry post-fire, providing baseline values for future comparisons. Our findings suggest that fire regimes select for particular mycorrhizal fungal communities but that responses are decoupled between community composition and function three years post-fire, highlighting the resilience of mycorrhizal function under varying fire regimes.

Increasing the resilience of individual plants and ecosystems is investigated through the dynamism of plant-soil interactions. The rhizosphere, the spatial zone outside the root surface area, is the gateway for intercellular associations between the plant and soil-borne organisms which heavily influence plant function. Where relevant environmental factors can be controlled, experimental research has highlighted the role of phylogeny in driving rhizosphere construction. This study investigated the composition and diversity of six co-occurring plant-hosts in native forest of SE NSW, with varying levels of phylogenetic diversity (2 Corymbia, 1 Eucalyptus and 3 Acacia). The authors hypothesised that the emphasis on phylogeny obscures the role of the ecological function of the plant-host on the construction of species- and genus-specific rhizospheres. Results indicate that each plant host produces a unique rhizosphere 'fingerprint' which collectively maximise use of the significant biodiversity found in native and unmanaged soils. The patterns of assembly within genus show conserved up- and down-regulation patterns in the Acacia plant-hosts that are not replicated with the Eucalyptus group. This suggests that phylogeny is a strong predictive element in rhizosphere construction, only where the genus has more consistency in ecological functions. As a result, this study suggests ecological function, particularly regarding the plant-hosts role in stoichiometry, is a valuable lens through which to investigate differences in plant-host soil microbiome assembly.

In Australia’s arid rangelands, the biodiversity of native perennial vegetation is threatened by the absence of appreciable recruitment of palatable vegetation associated with livestock grazing, resulting in what is termed "living dead" populations. While the pervasive effect of livestock preferential herbivory on vegetation biodiversity is well-documented, the indirect impacts on soil microbes and their vital role in facilitating plant recruitment remain largely unexplored in arid ecosystems.

We studied differences in soil physicochemistry and microbial community structure and function in grazed paddocks and nearby areas from which stock have been excluded for 100 years (TGB Osborn Reserve, Koonamore, in the arid north-eastern rangelands of South Australia). Soil was collected from beneath the canopies of perennial plants and from open areas, and used to test the germination and growth of mulga (Acacia aneura) under controlled glasshouse conditions. Environmental DNA analysis was used to identify soil microbial communities and their functions, which were analysed alongside soil nutrient content and plant growth measurements.

Our results reveal the complex factors that affect plant germination and growth, which differ spatially. Plants in soil exposed to low grazing intensity and ungrazed areas, collected from under canopies, show markedly greater growth than those from open soils. However, plants in soil from high-intensity grazed areas, both in canopy and open areas, display reduced overall growth, indicating that adverse impacts on ecosystem services provided by soils are not restricted to open spaces. Plant growth responses corresponding to differences in both soil nutrient levels and microbial community compositions and functional roles will be presented, providing novel insights into the pathways by which livestock indirectly impact ecosystem function in Australia’s arid ecosystems.

Soil microbes play an important role in the terrestrial phosphorus (P) cycle. In the absence of major deposition events or other disturbances, the activity of the soil microbial community will strongly influence the composition and bioavailability of compounds within the soil P pool. For example, the limitation of environmental phosphate will induce the differential expression of hundreds of functional traits, here defined as a gene-encoded characteristic of a cell’s metabolism, morphology or behaviour, and whose fitness is influenced by the extracellular environment. The relative abundance, diversity and expression of these traits is commonly used by investigators to infer the influence of microbially mediated processes on the terrestrial P cycle at large spatial scales. At these scales, however, the interpretation of these traits becomes detached from their ecological context. In particular, it becomes difficult to disentangle the effects of environmental filtering —i.e. from strong climactic and edaphic gradients— on microbial P cycling from other eco-evolutionary processes operating at finer spatial scales. This complicates efforts to link fine-scale microbial processes to larger patterns within the terrestrial P cycle. To address this, I present the S.A.T.E. framework of P acquisition and metabolism in soil bacteria and archaea. This framework groups the most commonly expressed traits observed in these organisms under conditions of phosphate limitation into four generalized ecological strategies. These include (i) the solubilization of bound P forms, (ii) antagonism, (iii) the tolerance of long-term P limitation, and (iv) the exploitation of alternative P forms. I propose that the relative expression of these strategies at the cellular level emerges from logical eco-evolutionary trade-offs in trait fitness. This novel framework provides a conceptual basis for investigators to mechanistically link the ecological dynamics of soil bacteria and archaea at fine spatial scales to larger processes within the terrestrial P cycle.

Most crops associate with AM fungi in a symbiosis that can enhance their access to nutrients and water and augment disease resistance. AM fungal communities are partly determined by plant host identity, which may be related to particular traits among genotypes such as the sensitivity to soil P, by root traits such as specific root length (SRL), and by soil properties. Here we investigated how soil P availability affects the assembly of root-colonizing AM fungi among Sorghum bicolor genotypes. We conducted a factorial pot experiment where three genotypes of S. bicolor were grown under low and high P treatments and exposed to two different but natural AM fungal communities (AM1, AM2), and observed at two harvest time points. We found that: (1) under AM2 and low P treatments, 'Resolute' showed dramatic growth benefits over other genotypes of S. bicolor, with increases in root biomass (104%-192%), shoot biomass (164%-259%), photosynthetic rate (8%-15%), chlorophyll content (40%-48%), leaf N (261%-390%), and P (261%-353%) contents; (2) Under AM2 and later harvest time point, 'Resolute' had contrasting SRL and AM fungal community composition in low and high P treatment, which indicates that SRL modulated fungal community to optimize nutrient acquisition; (3) Low taxonomic but high phylogenetic diversity in AM fungal communities explained the differences of growth benefits among genotypes; and (4) A joint species distribution model, which simultaneously analyzes multiple fungal species and their co-occurrence patterns, identified key factors driving the assembly of root-colonizing AM fungi. Our results suggest that that targeting specific host genotypes in breeding programs is a key strategy to utilize beneficial fungal communities, especially for the world's fifth-largest cereal crop -- S. bicolor, advancing agricultural sustainability and food security with reduced chemical inputs.

Charcoal rot, a disease of Sorghum bicolor caused by Macrophomina spp., is of particular concern under high temperatures and drought stress. The necrotrophic pathogen invades vascular tissues, disrupting water and nutrient transport, which leads to water stress, nutrient deficiencies, stalk rot, and yield losses. Macrophomina persists in soil for up to 15 years as microsclerotia and has a wide host range, rendering traditional management ineffective; alternative approaches to enhance crop resistance and mitigate disease severity are needed. Beneficial microbes, such as arbuscular mycorrhizal (AM) fungi, offer a promising avenue; they form complex root symbioses that enhance nutrient and water uptake, prime systemic defence and influence key metabolites, such as flavonoids and terpenoids, which play crucial roles in pathogen resistance. These defence-enhancing effects depend on AM fungal community composition, yet how a pathogen, such as Macrophomina, affects AM fungal diversity and AM-mediated resistance in sorghum remains unclear.

We conducted a factorial glasshouse experiment in which sorghum was grown without arbuscular mycorrhizal (AM) fungi or with one of two AM fungal communities, and inoculated M.phaseolina, or left pathogen-free. Plants were imaged throughout and harvested at three timepoints to quantify biomass, nutrients, salicylic acid (SA) and abscisic acid (ABA) by GC-MS; root AM fungal composition was profiled through 18S DNA metabarcoding.

AM fungal identity shaped both defence and growth. Community-I reduced charcoal rot lesions by 72.6%, while Community-II did not, yet Community-II increased total biomass by 36.7% versus non-mycorrhizal controls. Pathogen infection reversed colonisation, with Community-II declining from 60% to 34% and Community-I rose from 30% to 56%. Mycorrhizal plants had twice the foliar phosphorus, especially Community-II, and pathogen and drought-induced ABA spikes were halved by both communities. Community-I thus offers sustained disease suppression, whereas Community-II promotes biomass and P nutrition; combining functionally distinct AM consortia could safeguard sorghum under charcoal-rot pressure.