Soil physico-chemical properties are critical for predicting carbon storage and nutrient availability across Australia

Soil carbon and nutrient availability play crucial roles in ecosystem sustainability, and they are controlled by the interaction of climatic, biotic, and soil physico-chemical variables. Although soil physico-chemical properties have been recognized as vital variables for predicting soil organic carbon (SOC) and nutrients, their relative influence across broad geographical scales has yet to be evaluated when simultaneously considering many other drivers. Using boosted regression tree and structural equation modelling analyses of observations from topsoil (0-10 cm) and subsoil (20-30 cm) at 628 sites across Australia, we investigated the effects and relative influence of climate (mean annual temperature and aridity index), plant productivity, soil biodiversity (bacterial and fungal richness), and soil physical (clay and silt) and chemical (pH and iron) properties on SOC content and nutrient availability (i.e. nitrogen, phosphorus, and potassium). Among these variables, we found that soil physico-chemical properties primarily predicted the continent-scale SOC storage and nutrient availability. In contrast, climate, plant productivity, and soil biodiversity played relatively small roles. The importance of physico-chemical properties was evident across soil depths and ecosystem types (i.e. tropical, temperate, arid, and cropland). Our findings point to the need to better understand the role of soil physico-chemical properties in soil carbon and nutrient cycling and including these variables in predictions of SOC and nutrient dynamics at the ecosystem to continental scale

Wildfire impact : natural experiment reveals differential short-term changes in soil microbial communities

A wildfire which overran a sensor network site provided an opportunity (a natural experiment) to monitor short-term post-fire impacts (immediate and up to three months post-fire) in remnant eucalypt woodland and managed pasture plots. The magnitude of fire-induced changes in soil properties and soil microbial communities was determined by comparing (1) variation in fire-adapted eucalypt woodland vs. pasture grassland at the burnt site; (2) variation at the burnt woodland-pasture sites with variation at two unburnt woodland-pasture sites in the same locality; and (3) temporal variation pre- and post-fire. In the eucalypt woodland, soil ammonium, pH and ROC content increased post-fire, while in the pasture soil, soil nitrate increased post-fire and became the dominant soluble N pool. However, apart from distinct changes in N pools, the magnitude of change in most soil properties was small when compared to the unburnt sites. At the burnt site, bacterial and fungal community structure showed significant temporal shifts between pre- and post-fire periods which were associated with changes in soil nutrients, especially N pools. In contrast, microbial communities at the unburnt sites showed little temporal change over the same period. Bacterial community composition at the burnt site also changed dramatically post-fire in terms of abundance and diversity, with positive impacts on abundance of phyla such as Actinobacteria, Proteobacteria and Firmicutes. Large and rapid changes in soil bacterial community composition occurred in the fire-adapted woodland plot compared to the pasture soil, which may be a reflection of differences in vegetation composition and fuel loading. Given the rapid yet differential response in contrasting land uses, identification of key soil bacterial groups may be useful in assessing recovery of fire-adapted ecosystems, especially as wildfire frequency is predicted to increase with global climate change

A consensus guide to capturing the ability to inhibit actions and impulsive behaviors in the stop-signal task.

Response inhibition is essential for navigating everyday life. Its derailment is considered integral to numerous neurological and psychiatric disorders, and more generally, to a wide range of behavioral and health problems. Response-inhibition efficiency furthermore correlates with treatment outcome in some of these conditions. The stop-signal task is an essential tool to determine how quickly response inhibition is implemented. Despite its apparent simplicity, there are many features (ranging from task design to data analysis) that vary across studies in ways that can easily compromise the validity of the obtained results. Our goal is to facilitate a more accurate use of the stop-signal task. To this end, we provide 12 easy-to-implement consensus recommendations and point out the problems that can arise when they are not followed. Furthermore, we provide user-friendly open-source resources intended to inform statistical-power considerations, facilitate the correct implementation of the task, and assist in proper data analysis

Fungal genome size and composition reflect ecological strategies along soil fertility gradients

Genomic traits reflect the evolutionary processes that have led to ecological variation among extant organisms, including variation in how they acquire and use resources. Soil fungi have diverse nutritional strategies and exhibit extensive variation in fitness along resource gradients. We tested for trade-offs in genomic traits with mycelial nutritional traits and hypothesize that such trade-offs differ among fungal guilds as they reflect contrasting resource exploitation and habitat preferences. We found species with large genomes exhibited nutrient-poor mycelium and low GC content. These patterns were observed across fungal guilds but with varying explanatory power. We then matched trait data to fungal species observed in 463 Australian grassland, woodland and forest soil samples. Fungi with large genomes and lower GC content dominated in nutrient-poor soils, associated with shifts in guild composition and with species turnover within guilds. These findings highlight fundamental mechanisms that underpin successful ecological strategies for soil fungi

Using genetic tools to diagnose dieback in Parkinsonia aculeata

Dieback in invasive and agricultural plants is a common phenomenon attributed to a range of abiotic and biotic factors. In this project we are investigating the link between the introduction and establishment of a non-native plant to a new range and the subsequent dying-back of the invasive population. We are focusing on possible pathogen-related causes for dieback, especially considering the following three scenarios: 1. re-association with pathogens from the non-native’s native range, 2. new association with pathogens in the introduced range, and 3. association with cosmopolitan pathogens

Triggering dieback in an invasive plant : endophyte diversity and pathogenicity

Dieback causes a progressive reduction in plant population health, resulting in the death of plant parts and often plant death. It is prevalent in many invasive woody weeds in Australia and has been suggested as a potential mechanism for biocontrol of these species. Parkinsonia aculeata one such invasive tree in northern Australia. It has naturalised across a wide range of climatic zones and some populations have been heavily reduced by dieback occurrence. The cause(s) of dieback in parkinsonia remain elusive, although fungal endophytes have been previously implicated. In this study, we characterised the culturable fungal endophyte community of healthy and dieback-affected parkinsonia using culture-based techniques, and identified cultured isolates via amplicon sequencing of the internal transcribed spacer (ITS) of the rDNA operon. Eight isolates, identified as pathogens, were selected for a 10-week pathogenicity trial, including water stress treatments, on parkinsonia seedlings. We isolated a taxonomically diverse fungal community from parkinsonia, representing 54 unique species from 25 families. Communities were similar across healthy and dieback-affected plants, but differed by plant tissue. Of the eight putative pathogenic isolates tested in the pathogenicity trial, inoculation with Lasiodiplodia pseudotheobromae, Botryosphaeria dothidea and Pestalotiopsis mangiferae resulted in the largest lesions, but systemic infection or dieback-like symptoms were not observed in any treatment despite plant stress being induced by drought or inundation. We concluded that inoculation of parkinsonia with the tested putative fungal pathogens is unlikely to result in dieback, which has implications for future work in biocontrol of parkinsonia

Endophyte community composition is associated with dieback occurrence in an invasive tree

Background and aims Dieback is pervasive in many populations of invasive woody weeds globally. Previous studies on dieback have focused on specific potential causative biotic agents, but most cases remain unexplained. The potential role of endophytic microbial communities in dieback, including the relative importance of endophytes with pathogenic or protective capabilities, remains poorly studied. We tested whether changes in archaeal, bacterial and fungal endophyte community structure is associated with dieback occurrence in the invasive, leguminous tree, Parkinsonia aculeata L. (parkinsonia). Methods We sampled roots, stems and stem tips from healthy and dieback-affected parkinsonia and conducted terminal restriction fragment length polymorphism (TRFLP) analysis on DNA extracted from these samples using domain-specific primers for archaea, bacteria and higher fungi. Results Microbial community composition strongly differed with parkinsonia disease status (archaea, bacteria and fungi) and plant part (archaea and fungi). Plant part and disease status effects were strongest in archaea. We also found evidence implicating both pathogenic and potentially protective endophytes in the onset of dieback. Conclusions This is the first study that has shown significant associations between changes in endophyte community composition and dieback presence. Our results highlight the complexity of those changes and provide support for the hypothesis that diverse pathogenic and protective endophytes may be implicated in dieback

Ecological drivers of soil microbial diversity and soil biological networks in the Southern Hemisphere

The ecological drivers of soil biodiversity in the Southern Hemisphere remain underexplored. Here, in a continental survey comprising 647 sites, across 58 degrees of latitude between tropical Australia and Antarctica, we evaluated the major ecological patterns in soil biodiversity and relative abundance of ecological clusters within a co-occurrence network of soil bacteria, archaea and eukaryotes. Six major ecological clusters (modules) of co-occurring soil taxa were identified. These clusters exhibited strong shifts in their relative abundances with increasing distance from the equator. Temperature was the major environmental driver of the relative abundance of ecological clusters when Australia and Antarctica are analyzed together. Temperature, aridity, soil properties and vegetation types were the major drivers of the relative abundance of different ecological clusters within Australia. Our data supports significant reductions in the diversity of bacteria, archaea and eukaryotes in Antarctica vs. Australia linked to strong reductions in temperature. However, we only detected small latitudinal variations in soil biodiversity within Australia. Different environmental drivers regulate the diversity of soil archaea (temperature and soil carbon), bacteria (aridity, vegetation attributes and pH) and eukaryotes (vegetation type and soil carbon) across Australia. Together, our findings provide new insights into the mechanisms driving soil biodiversity in the Southern Hemisphere

Ecological drivers of soil microbial diversity and soil biological networks in the Southern Hemisphere

The ecological drivers of soil biodiversity in the Southern Hemisphere remain underexplored. Here, in a continental survey comprising 647 sites, across 58 degrees of latitude between tropical Australia and Antarctica, we evaluated the major ecological patterns in soil biodiversity and relative abundance of ecological clusters within a co-occurrence network of soil bacteria, archaea and eukaryotes. Six major ecological clusters (modules) of co-occurring soil taxa were identified. These clusters exhibited strong shifts in their relative abundances with increasing distance from the equator. Temperature was the major environmental driver of the relative abundance of ecological clusters when Australia and Antarctica are analyzed together. Temperature, aridity, soil properties and vegetation types were the major drivers of the relative abundance of different ecological clusters within Australia. Our data supports significant reductions in the diversity of bacteria, archaea and eukaryotes in Antarctica vs. Australia linked to strong reductions in temperature. However, we only detected small latitudinal variations in soil biodiversity within Australia. Different environmental drivers regulate the diversity of soil archaea (temperature and soil carbon), bacteria (aridity, vegetation attributes and pH) and eukaryotes (vegetation type and soil carbon) across Australia. Together, our findings provide new insights into the mechanisms driving soil biodiversity in the Southern Hemisphere

Characterisation of above-ground endophytic and soil fungal communities associated with dieback-affected and healthy plants in five exotic invasive species

In Australia, several well-established invasive plant species have experienced unexplained dieback. To investigate this issue, we used internal transcribed spacer (ITS) amplicon pyrosequencing to characterise fungal communities within stems (endophytes) and soils associated with dieback-affected and healthy plants from populations of five exotic invasive species (Jatropha gossypiifolia, Mimosa pigra, Parkinsonia aculeata, Tamarix aphylla and Vachellia nilotica) across northern Australia. M. pigra and P.\ua0aculeata were sampled from multiple geographic regions. A total of 353 and 4926 fungal operational taxonomic units (OTUs) were identified in stem and soil samples, respectively. Members of Ascomycota were common, representing 75% of stem and 49% of soil OTUs. Four common endophytes, including Cladosporium perangustum, were at least 50% more prevalent in healthy than dieback-affected samples for the five invasive species combined. Fungal community structure within stem and soil samples varied among invasive species. For the two species sampled across multiple regions, M. pigra had similar fungal communities within stems among regions, but a significant difference in associated soil fungi, suggesting that host plant rather than environment determined endophytic communities in this species. Irrespective of the invasive species and sample type (stem vs. soil), no significant differences were observed in fungal richness, diversity or community structure between dieback-affected and healthy plants, either locally or regionally. Our work failed to identify fungi that were either unique or relatively more abundant in dieback than healthy plants in these invasive species. Future investigations of biotic factors other than fungi, such as bacteria, archaea and oomycetes, may provide more insights into the mechanism of the dieback phenomenon affecting these species