Agricultural land-use favours Mucoromycotinian, but not Glomeromycotinian, arbuscular mycorrhizal fungi across ten biomes.

Globally, agricultural land-use negatively affects soil biota that contribute to ecosystem functions such as nutrient cycling, yet arbuscular mycorrhizal fungi (AMF) are promoted as essential components of agroecosystems. Arbuscular mycorrhizal fungi include Glomeromycotinian AMF (G-AMF) and the arbuscule-producing fine root endophytes, recently re-classified into the Endogonales order within Mucoromycotina. The correct classification of Mucoromycotinian AMF (M-AMF) and the availability of new molecular tools can guide research to better the understanding of their diversity and ecology. To investigate the impact on G-AMF and M-AMF of agricultural land-use at a continental scale, we sampled DNA from paired farm and native sites across 10 Australian biomes. Glomeromycotinian AMF were present in both native and farm sites in all biomes. Putative M-AMF were favoured by farm sites, rare or absent in native sites, and almost entirely absent in tropical biomes. Temperature, rainfall, and soil pH were strong drivers of richness and community composition of both groups, and plant richness was an important mediator. Both fungal groups occupy different, but overlapping, ecological niches, with M-AMF thriving in temperate agricultural landscapes. Our findings invite exploration of the origin and spread of M-AMF and continued efforts to resolve the phylogeny of this newly reclassified group of AMF.

Evidence for Niche Differentiation in the Environmental Responses of Co-occurring Mucoromycotinian Fine Root Endophytes and Glomeromycotinian Arbuscular Mycorrhizal Fungi.

Fine root endophytes (FRE) were traditionally considered a morphotype of arbuscular mycorrhizal fungi (AMF), but recent genetic studies demonstrate that FRE belong within the subphylum Mucoromycotina, rather than in the subphylum Glomeromycotina with the AMF. These findings prompt enquiry into the fundamental ecology of FRE and AMF. We sampled FRE and AMF in roots of Trifolium subterraneum from 58 sites across temperate southern Australia. We investigated the environmental drivers of composition, richness, and root colonization of FRE and AMF by using structural equation modelling and canonical correspondence analyses. Root colonization by FRE increased with increasing temperature and rainfall but decreased with increasing phosphorus (P). Root colonization by AMF increased with increasing soil organic carbon but decreased with increasing P. Richness of FRE decreased with increasing temperature and soil pH. Richness of AMF increased with increasing temperature and rainfall but decreased with increasing soil aluminium (Al) and pH. Aluminium, soil pH, and rainfall were, in decreasing order, the strongest drivers of community composition of FRE; they were also important drivers of community composition of AMF, along with temperature, in decreasing order: rainfall, Al, temperature, and soil pH. Thus, FRE and AMF showed the same responses to some (e.g. soil P, soil pH) and different responses to other (e.g. temperature) key environmental factors. Overall, our data are evidence for niche differentiation among these co-occurring mycorrhizal associates.

Soil microbes of an urban remnant riparian zone have greater potential for N removal than a degraded riparian zone.

Soils in the riparian zone, the interface between terrestrial and aquatic ecosystems, may decrease anthropogenic nitrogen (N) loads to streams through microbial transformations (e.g., denitrification). However, the ecological functioning of riparian zones is often compromised due to degraded conditions (e.g., vegetation clearing). Here we compare the efficacy of an urban remnant and a cleared riparian zone for supporting a putative denitrifying microbial community using 16S rRNA sequencing and quantitative polymerase chain reaction of archaeal and bacterial nitrogen cycling genes. Although we had no direct measure of denitrification rates, we found clear patterns in the microbial communities between the sites. Greater abundance of N-cycling genes was predicted by greater soil ammonium (N-NH4 ), organic phosphorus, and C:N. At the remnant site, we found positive correlations between microbial community composition, which was dominated by putative N oxidisers (Nitrosomonadaceae, Nitrospiraceae and Nitrosotaleaceae), and abundance of ammonia-oxidizing archaea (AOA), nirS, nirK and nosZ, whereas the cleared site had lower abundance of N-oxidisers and N cycling genes. These results were especially profound for the remnant riparian fringe, which suggests that this region maintains suitable soil conditions (via diverse vegetation structure and periodic saturation) to support putative N cyclers, which could amount to higher potential for N removal.

Biodegradability of polar compounds formed from weathered diesel.

Once released into the environment, petroleum is exposed to biological and physical weathering processes which can lead to the formation and accumulation of highly recalcitrant polar compounds. These polar compounds are often challenging to analyse and can be present as an "unresolved complex mixture" (UCM) in total petroleum hydrocarbon (TPH) analyses and can be mistaken for natural organic matter. Existing research on UCMs comprised of polar compounds is limited, with a majority of the compounds remaining unidentified and their long-term persistence unknown. Here, we investigated the potential biodegradation of these recalcitrant polar compounds isolated from weathered diesel contaminant, and the changes in the microbial community composition associated with the biodegradation process. Microcosms were used to study the biodegradability of the polar compounds under various aerobic and anaerobic conditions and the results compared against the biodegradation of fresh diesel. Under all conditions tested, the majority of the polar UCM contaminant remained recalcitrant to biodegradation. The degradation was limited to the TPH portion of the polar UCM, which represented a minor fraction of the total polar UCM concentration. Changes in microbial community composition were observed under different redox conditions and in the presence of different contaminants. This work furthers the understanding of the biodegradation and long-term recalcitrance of polar compounds formed through weathering at contaminated legacy sites.

COVID-19 vaccination uptake and hesitancy reasons in food production workers.

BACKGROUND: Food production sites have been a high-risk location for SARS-CoV-2 outbreaks worldwide since early in the COVID-19 pandemic. Ireland has a high population rate of COVID-19 vaccination, but reports from food production sites suggest uptake is lower amongst workers despite prior outbreaks at these workplaces. AIMS: To study COVID-19 vaccination rates, intent to undertake future vaccination and hesitancy reasons in food production workers. METHODS: Data regarding vaccination status was collected via an online survey from workers at 8 food production sites in Ireland; those who were unvaccinated were asked for reasons for being unvaccinated and likelihood to future vaccination. Respondents were also asked for their usual trusted source of medical information. RESULTS: N = 355 responses were received. The crude vaccination rate is 86% (N = 306). Those employed in the general operative class are more likely to be unvaccinated (N = 30; 18%) when compared to unvaccinated in all other job classes (N = 16; 9%: p < 0.01). The rate of vaccination is lower in those not born in Ireland compared to those born in Ireland (N = 110, 73% vs N = 192; 98%: p < 0.001). N = 35 (76%) of unvaccinated workers report they are very unlikely or unlikely to undertake vaccination in the future. CONCLUSIONS: There is an observed lower-than-national vaccination rate in food production workers. Rates are lowest amongst those workers born overseas; targeting these groups with information responding to their concerns may increase uptake and reduce current and future health inequalities.

Soil microbial community successional patterns during forest ecosystem restoration.

Soil microbial community characterization is increasingly being used to determine the responses of soils to stress and disturbances and to assess ecosystem sustainability. However, there is little experimental evidence to indicate that predictable patterns in microbial community structure or composition occur during secondary succession or ecosystem restoration. This study utilized a chronosequence of developing jarrah (Eucalyptus marginata) forest ecosystems, rehabilitated after bauxite mining (up to 18 years old), to examine changes in soil bacterial and fungal community structures (by automated ribosomal intergenic spacer analysis [ARISA]) and changes in specific soil bacterial phyla by 16S rRNA gene microarray analysis. This study demonstrated that mining in these ecosystems significantly altered soil bacterial and fungal community structures. The hypothesis that the soil microbial community structures would become more similar to those of the surrounding nonmined forest with rehabilitation age was broadly supported by shifts in the bacterial but not the fungal community. Microarray analysis enabled the identification of clear successional trends in the bacterial community at the phylum level and supported the finding of an increase in similarity to nonmined forest soil with rehabilitation age. Changes in soil microbial community structure were significantly related to the size of the microbial biomass as well as numerous edaphic variables (including pH and C, N, and P nutrient concentrations). These findings suggest that soil bacterial community dynamics follow a pattern in developing ecosystems that may be predictable and can be conceptualized as providing an integrated assessment of numerous edaphic variables.

Natural attenuation of legacy hydrocarbon spills in pristine soils is feasible despite difficult environmental conditions in the monsoon tropics.

The Kimberley region of Western Australia is a National Heritage listed region that is internationally recognised for its environmental and cultural significance. However, petroleum spills have been reported at a number of sites across the region, representing an environmental concern. The region is also characterised as having low soil nutrients, high temperatures and monsoonal rain - all of which may limit the potential for natural biodegradation of petroleum. Therefore, this work evaluated the effect of legacy petroleum hydrocarbons on the indigenous soil microbial community (across the domains Archaea, Bacteria and Fungi) at three sites in the Kimberley region. At each site, soil cores were removed from contaminated and control areas and analysed for total petroleum hydrocarbons, soil nutrients, pH and microbial community profiling (using16S rRNA and ITS sequencing on the Illumina MiSeq Platform). The presence of petroleum hydrocarbons decreased microbial diversity across all kingdoms, altered the structure of microbial communities and increased the abundance of putative hydrocarbon degraders (e.g. Mycobacterium, Acremonium, Penicillium, Bjerkandera and Candida). Microbial community shifts from contaminated soils were also associated with an increase in soil nutrients (notably Colwell P and S). Our study highlights the long-term effect of legacy hydrocarbon spills on soil microbial communities and their diversity in remote, infertile monsoonal soils, but also highlights the potential for natural attenuation to occur in these environments.

Low pore connectivity increases bacterial diversity in soil.

One of soil microbiology's most intriguing puzzles is how so many different bacterial species can coexist in small volumes of soil when competition theory predicts that less competitive species should decline and eventually disappear. We provide evidence supporting the theory that low pore connectivity caused by low water potential (and therefore low water content) increases the diversity of a complex bacterial community in soil. We altered the pore connectivity of a soil by decreasing water potential and increasing the content of silt- and clay-sized particles. Two textures were created, without altering the chemical properties or mineral composition of the soil, by adding silt- and clay-sized particles of quartz to a quartz-based sandy soil at rates of 0% (sand) or 10% (silt+clay). Both textures were incubated at several water potentials, and the effect on the active bacterial communities was measured using terminal restriction fragment length polymorphism (TRFLP) of bacterial 16S rRNA. Bacterial richness and diversity increased as water potential decreased and soil became drier (P < 0.012), but they were not affected by texture (P > 0.553). Bacterial diversity increased at water potentials of

An agricultural practise with climate and food security benefits: "Claying" with kaolinitic clay subsoil decreased soil carbon priming and mineralisation in sandy cropping soils.

As the agricultural sector seeks to feed a growing global population, climate-smart agriculture offers opportunities to concurrently mitigate climate change by reducing greenhouse gas emissions and/or increasing carbon storage in soils. This study examined the potential for clay addition to reduce CO2 emissions from plant residues and soil organic matter in a sandy soil. Soils were sourced from a 15-year-old field trial where claying (200 t ha-1) had already demonstrated improvements in water infiltration, grain yield and profits. Isotopically labelled plant residues (wheat, canola, or pea) were used to separate residue-derived and soil-derived CO2 sources from a nil-clay control, a historically clayed, and two freshly created soils with either high (10%) or low (3%) subsoil clay additions. Laboratory incubations demonstrated that historically clayed soils released less CO2 from plant residues and soil organic matter. Clay addition also decreased the priming effect of adding fresh residue to soils. The results from clay experimentally added in the laboratory varied. Differences in chemical and biological indicators (pH, microbial biomass C and N, extractable organic C and N, NO3-, NH4+, abundance of bacterial, archaeal, fungal, LMCO, GH48 and CbhI genes) did not correlate with patterns of CO2 emissions across treatments. While claying practices have previously demonstrated benefits to crop productivity, this research demonstrates long-term changes in carbon-cycling that could promote greater carbon sequestration.

Root microbiomes as indicators of seagrass health.

The development of early warning indicators that identify ecosystem stress is a priority for improving ecosystem management. As microbial communities respond rapidly to environmental disturbance, monitoring their composition could prove one such early indicator of environmental stress. We combined 16S rRNA gene sequencing of the seagrass root microbiome of Halophila ovalis with seagrass health metrics (biomass, productivity and Fsulphide) to develop microbial indicators for seagrass condition across the Swan-Canning Estuary and the Leschenault Estuary (south-west Western Australia); the former had experienced an unseasonal rainfall event leading to declines in seagrass health. Microbial indicators detected sites of potential stress that other seagrass health metrics failed to detect. Genera that were more abundant in 'healthy' seagrasses included putative methylotrophic bacteria (e.g. Methylotenera and Methylophaga), iron cycling bacteria (e.g. Deferrisoma and Geothermobacter) and N2 fixing bacteria (e.g. Rhizobium). Conversely, genera that were more abundant in 'stressed' seagrasses were dominated by putative sulphur-cycling bacteria, both sulphide-oxidising (e.g. Candidatus Thiodiazotropha and Candidatus Electrothrix) and sulphate-reducing (e.g. SEEP-SRB1, Desulfomonile and Desulfonema). The sensitivity of the microbial indicators developed here highlights their potential to be further developed for use in adaptive seagrass management, and emphasises their capacity to be effective early warning indicators of stress.

Soil Salinity and pH Drive Soil Bacterial Community Composition and Diversity Along a Lateritic Slope in the Avon River Critical Zone Observatory, Western Australia.

Soils are crucial in regulating ecosystem processes, such as nutrient cycling, and supporting plant growth. To a large extent, these functions are carried out by highly diverse and dynamic soil microbiomes that are in turn governed by numerous environmental factors including weathering profile and vegetation. In this study, we investigate geophysical and vegetation effects on the microbial communities of iron-rich lateritic soils in the highly weathered landscapes of Western Australia (WA). The study site was a lateritic hillslope in southwestern Australia, where gradual erosion of the duricrust has resulted in the exposure of the different weathering zones. High-throughput amplicon sequencing of the 16S rRNA gene was used to investigate soil bacterial community diversity, composition and functioning. We predicted that shifts in the microbial community would reflect variations in certain edaphic properties associated with the different layers of the lateritic profile and vegetation cover. Our results supported this hypothesis, with electrical conductivity, pH and clay content having the strongest correlation with beta diversity, and many of the differentially abundant taxa belonging to the phyla Actinobacteria and Proteobacteria. Soil water repellence, which is associated with Eucalyptus vegetation, also affected beta diversity. This enhanced understanding of the natural system could help to improve future crop management in WA since the physicochemical properties of the agricultural soils in this region are inherited from laterites via the weathering and pedogenesis processes.

Implications of co-contamination with aged heavy metals and total petroleum hydrocarbons on natural attenuation and ecotoxicity in Australian soils.

The bioremediation of historic industrial contaminated sites is a complex process. Co-contamination, often with lead which was commonly added to gasoline until 16 years ago is one of the biggest challenges affecting the clean-up of these sites. In this study, the effect of heavy metals, as co-contaminant, together with total petroleum hydrocarbons (TPH) is reported, in terms of remaining soil toxicity and the structure of the microbial communities. Contaminated soil samples from a relatively hot and dry climate in Western Australia were collected (n = 27). Analysis of soils showed the presence of both contaminants, TPHs and heavy metals. The Microtox test confirmed that their co-presence elevated the remaining ecotoxicity. Toxicity was correlated with the presence of lead, zinc and TPH (0.893, 0.599 and 0.488), respectively, assessed using Pearson Correlation coefficient factor. Next Generation Sequencing of soil bacterial 16S rRNA, revealed a lack of dominate genera; however, despite the variation in soil type, a few genera including Azospirillum spp. and Conexibacter were present in most soil samples (85% and 82% of all soils, respectively). Likewise, many genera of hydrocarbon-degrading bacteria were identified in all soil samples. Streptomyces spp. was presented in 93% of the samples with abundance between 7% and 40%. In contrast, Acinetobacter spp. was found in only one sample but was a dominant member of (45%) of the microbial community. In addition, some bacterial genera were correlated to the presence of the heavy metals, such as Geodermatophilus spp., Rhodovibrio spp. and Rubrobacter spp. which were correlated with copper, lead and zinc, respectively. This study concludes that TPH and heavy metal co-contamination significantly elevated the associated toxicity. This is an important consideration when carrying out risk assessment associated with natural attenuation. This study also improves knowledge about the dynamics of microbial communities in mixed contamination scenarios.

Metagenomic Evidence of Microbial Community Responsiveness to Phosphorus and Salinity Gradients in Seagrass Sediments.

Sediment microorganisms can have profound influence on productivity and functioning of marine ecosystems through their critical roles in regulating biogeochemical processes. However, the identity of sediment microorganisms that mediate organic matter turnover and nutrient cycling in seagrass sediments is only poorly understood. Here, we used metagenomic sequencing to investigate shifts in the structure and functioning of the microbial community of seagrass sediments across a salinity and phosphorus (P) availability gradient in Shark Bay, WA, Australia. This iconic ecosystem is oligotrophic and hypersaline with abundant seagrass meadows that directly contribute Shark Bay's status as a World Heritage Site. We show that sediment phosphonate metabolism genes as well as enzyme activities increase in hypersaline conditions with lower soluble reactive phosphate in the water column. Given that sediment organic P content is also highest where P concentrations in the water column are low, we suggest that microbial processing of organic P can contribute to the P requirements of seagrasses at particularly oligotrophic sites. Seagrass meadows are often highly productive in oligotrophic waters, and our findings suggest that an increase in the functional capacity of microbial communities in seagrass sediments to break down organic P may contribute to the high productivity of seagrass meadows under oligotrophic conditions. When compared to soil and sediment metagenomes from other aquatic and terrestrial ecosystems, we also show microbial communities in seagrass sediments have a disproportionately high abundance of putative phosphorus and sulfur metabolism genes, which may have played an important evolutionary role in allowing these angiosperms to recolonize the marine environment and prosper under oligotrophic conditions.

Altering the mineral composition of soil causes a shift in microbial community structure.

This study tests the hypothesis that altering the mineral composition of soil influences microbial community structure in a nutrient-deficient soil. Microcosms were established by adding mica (M), basalt (B) and rock phosphate (P) to soil separately, and in combination (MBP), and by planting with Lolium rigidum, Trifolium subterraneum or by leaving unplanted. The effects of mineral and plant treatments on microbial community structure were assessed using automated ribosomal intergenic spacer analysis. Bacterial community structure was significantly affected by both mineral (global R=0.73 and P<0.001) and plant (global R=0.71 and P<0.001) treatments, as was the fungal community structure: mineral (global R=0.65 and P<0.001) and plant (global R=0.65 and P<0.001) treatments. All pairwise comparisons of bacterial and fungal communities between different mineral treatments and between different plant treatments were significantly different (P<0.05). This study has shown that mineral addition to soil microcosms resulted in substantial changes in both bacterial and fungal community structure, dependent on the type of mineral added and the plant species present. These results suggest that the mineral composition of soil may be an important factor influencing the microbial community structure in soil.

Response of microbial biomass and CO2-C loss to wetting patterns are temperature dependent in a semi-arid soil.

One of the greatest contemporary challenges in terrestrial ecology is to determine the impact of climate change on the world's ecosystems. Here we investigated how wetting patterns (frequency and intensity) and nutrient additions altered microbial biomass and CO2-C loss from a semi-arid soil. South-western Australia is predicted to experience declining annual rainfall but increased frequency of summer rainfall events when soil is fallow. Agricultural soils (0-10 cm at 10 °C or 25 °C) received the same total amount of water (15 mL over 30 days) applied at different frequency; with either nil or added nitrogen and phosphorus. Smaller more frequent wetting applications resulted in less CO2-C loss (P < 0.001); with cumulative CO2-C loss 35% lower than a single wetting event. This coincided with increased microbial biomass C at 25 °C but a decline at 10 °C. Increasing nutrient availability decreased CO2-C loss only under a single larger wetting event. While bacterial and fungal abundance remained unchanged, archaeal abundance and laccase-like copper monooxidase gene abundance increased with more frequent wetting at 25 °C. Our findings suggest smaller more frequent summer rainfall may decrease CO2 emissions compared to infrequent larger events; and enhance microbial C use efficiency where sufficient background soil organic matter and nutrients are available.

Low Light Availability Alters Root Exudation and Reduces Putative Beneficial Microorganisms in Seagrass Roots.

Seagrass roots host a diverse microbiome that is critical for plant growth and health. Composition of microbial communities can be regulated in part by root exudates, but the specifics of these interactions in seagrass rhizospheres are still largely unknown. As light availability controls primary productivity, reduced light may impact root exudation and consequently the composition of the root microbiome. Hence, we analyzed the influence of light availability on root exudation and community structure of the root microbiome of three co-occurring seagrass species, Halophila ovalis, Halodule uninervis and Cymodocea serrulata. Plants were grown under four light treatments in mesocosms for 2 weeks; control (100% surface irradiance (SI), medium (40% SI), low (20% SI) and fluctuating light (10 days 20% and 4 days 100%). 16S rDNA amplicon sequencing revealed that microbial diversity, composition and predicted function were strongly influenced by the presence of seagrass roots, such that root microbiomes were unique to each seagrass species. Reduced light availability altered seagrass root exudation, as characterized using fluorescence spectroscopy, and altered the composition of seagrass root microbiomes with a reduction in abundance of potentially beneficial microorganisms. Overall, this study highlights the potential for above-ground light reduction to invoke a cascade of changes from alterations in root exudation to a reduction in putative beneficial microorganisms and, ultimately, confirms the importance of the seagrass root environment - a critical, but often overlooked space.

Environmental drivers of soil microbial community structure and function at the Avon River Critical Zone Observatory.

The Critical Zone is defined as the thin, permeable layer from the tops of the trees to the bottom of the bedrock that sustains terrestrial life on Earth. The geometry and shape of the various weathering zones are known as the critical zone architecture. At the centre of the Critical Zone are soils and the microorganisms that inhabit them. In Western Australia, the million-year-old stable weathering history and more recent lateral erosion during the past hundreds of thousands of years have created a geomorphic setting where deep weathering zones are now exposed on the surface along the flanks of many lateritic hills. These old weathering zones provide diverse physical and chemical properties that influence near surface pedologic conditions and thus likely shape current surface microbiology. Here, we present data derived from a small lateritic hill on the UWA Farm Ridgefield. Spatial soil sampling revealed the contrasting distribution patterns of simple soil parameters such as pH (CaCl2) and electric conductivity. These are clearly linked with underlying changes of the critical zone architecture and show a strong contrast with low values of pH3.3 at the top of the hill to pH5.3 at the bottom. These parameters were identified as major drivers of microbial spatial variability in terms of bacterial and archaeal community composition but not abundance. In addition, we used sensitive (14)C labelling to assess turnover of three model organic nitrogen compounds - an important biogeochemical functional trait relating to nutrient availability. Though generally rapid and in the order of rates reported elsewhere (t½<5h), some points in the sampling area showed greatly reduced turnover rates (t½>10h). In conclusion, we have shown that the weathering and erosion history of ancient Western Australia affects the surface pedology and has consequences for microbial community structure and function.

Increasing the Size of the Microbial Biomass Altered Bacterial Community Structure which Enhances Plant Phosphorus Uptake.

Agricultural production can be limited by low phosphorus (P) availability, with soil P being constrained by sorption and precipitation reactions making it less available for plant uptake. There are strong links between carbon (C) and nitrogen (N) availability and P cycling within soil P pools, with microorganisms being an integral component of soil P cycling mediating the availability of P to plants. Here we tested a conceptual model that proposes (i) the addition of readily-available organic substrates would increase the size of the microbial biomass thus exhausting the pool of easily-available P and (ii) this would cause the microbial biomass to access P from more recalcitrant pools. In this model it is hypothesised that the size of the microbial population is regulating access to less available P rather than the diversity of organisms contained within this biomass. To test this hypothesis we added mixtures of simple organic compounds that reflect typical root exudates at different C:N ratios to a soil microcosm experiment and assessed changes in soil P pools, microbial biomass and bacterial diversity measures. We report that low C:N ratio (C:N = 12.5:1) artificial root exudates increased the size of the microbial biomass while high C:N ratio (C:N = 50:1) artificial root exudates did not result in a similar increase in microbial biomass. Interestingly, addition of the root exudates did not alter bacterial diversity (measured via univariate diversity indices) but did alter bacterial community structure. Where C, N and P supply was sufficient to support plant growth the increase observed in microbial biomass occurred with a concurrent increase in plant yield.