Publications

Sulphate‐reducing bacteria (SRB) represent a key biological component of the global sulphur (S) cycle and are common in soils, where they reduce SO 4 2− to H 2 S during the anaerobic degradation of soil organic matter. The factors that regulate their distribution in soil, however, remain poorly understood. We sought to determine the ecological patterns of SRB richness within a nationwide 16S metabarcoding dataset. Across 436 sites belonging to seven contrasting temperate land uses (e.g., arable, grasslands, woodlands, heathland and bog), SRB richness was relatively low across land uses but greatest in grasslands and lowest in woodlands and peat‐rich soils. There was a shift in dominant SRB taxa from Desulfosporosinus and Desulfobulbus in arable and grassland land uses to Desulfobacca in heathland and bog sites. In contrast, richness of other generalist anaerobic bacterial taxa found in our dataset (e.g., Clostridium , Geobacter and Pelobacter ) followed a known trend of declining richness linked to land‐use productivity. Overall, the richness of SRBs and anaerobes had strong positive correlations with pH and sulphate concentration and strong negative relationships with elevation, soil organic matter, total carbon and carbon‐to‐nitrogen ratio. It is likely that these results reflect the driving influence of pH and competition for optimal electron acceptors with generalist anaerobic bacteria on SRB richness. Highlights Sulphate‐reducing bacteria (SRB) are key but rare soil biota that may compete with other anaerobes As UK sulphur deposition rates fall, local populations of SRB may also decline in soils Sulphate concentrations were higher in arable and wooded sites, not at higher elevation as expected SRB richness was lower than generalist anaerobes, with peaks in grasslands and a drop in lowland woods.

Calcareous soils are frequently characterized by the low bioavailability of plant nutrients. Consequently, many vascular plant species are unable to successfully colonize calcareous sites and the floristic composition of calcareous and acid silicate soils has been shown to differ markedly. The root exudation of oxalate and citrate has been suggested to play a pivotal role in same nutrient acquisition mechanisms operating in calcareous soils. The aim of this study was therefore to investigate the nutrient extraction efficiency of three individual organic acids commonly identified in root exudates, i.e. citric, malic and oxalic acid. Our results clearly demonstrate the context dependent nature of nutrient release by organic acids. The degree of P extraction was highly dependent on which organic acid was added, their concentration and pH, and their contact time with the soil. P is generally more efficiently extracted by organic acids at a high pH and follows the series oxalate>citrate>malate. The opposite relationship between pH and extraction efficiency was apparent for most other cations examined (e.g. Zn, Fe), which are more efficiently extracted by organic acids at low pH. A serious constraint to the ecological importance of organic acid exudation in response to P deficiency is, however, their very low P mobilization efficiency. For every mol of soil P mobilized, 1000mol of organic acid has to be added. It can, however, be speculated that in a calcareous soil with extremely low P concentrations it is still beneficial to the plants to exude organic acids in spite of the seemingly high costs in terms of carbon.

In monoculture, certain plant species are able to preferentially utilize different nitrogen (N) forms, both inorganic and organic, including amino acids and peptides, thus forming fundamental niches based on the chemical form of N. Results from field studies, however, are inconsistent: Some showing that coexisting plant species predominantly utilize inorganic N, while others reveal distinct interspecies preferences for different N forms. As a result, the extent to which hypothetical niches are realized in nature remains unclear. Here, we used in situ stable isotope tracer techniques to test the idea, in temperate grassland, that niche partitioning of N based on chemical form is related to plant productivity and the relative availability of organic and inorganic N. We also tested in situ whether grassland plants vary in their ability to compete for, and utilize peptides, which have recently been shown to act as an N source for plants in strongly N‐limited ecosystems. We hypothesized that plants would preferentially use NO 3 − ‐N and NH 4 + ‐N over dissolved organic N in high‐productivity grassland where inorganic N availability is high. On the other hand, in low‐productivity grasslands, where the availability of dissolved inorganic N is low, and soil availability of dissolved organic N is greater, we predicted that plants would preferentially use N from amino acids and peptides, prior to microbial mineralization. Turves from two well‐characterized grasslands of contrasting productivity and soil N availability were injected, in situ, with mixtures of 15 N‐labeled inorganic N ( NO 3 − and NH 4 + ) and 13 C 15 N labeled amino acid ( l ‐alanine) and peptide ( l ‐tri‐alanine). In order to measure rapid assimilation of these N forms by soil microbes and plants, the uptake of these substrates was traced within 2.5 hours into the shoots of the most abundant plant species, as well as roots and the soil microbial biomass. We found that, contrary to our hypothesis, the majority of plant species across both grasslands took up most N in the form of NH 4 + , suggesting that inorganic N is their predominant N source. However, we did find that organic N was a source of N which could be utilized by plant species at both sites, and in the low‐productivity grassland, plants were able to capture some tri‐alanine‐N directly. Although our findings did not support the hypothesis that differences in the availability of inorganic and organic N facilitate resource partitioning in grassland, they do support the emerging view that peptides represent a significant, but until now neglected, component of the terrestrial N cycle.

The movement of biological (genetic viral, fungal or bacterial) and chemical indicators (BCIs) within sewer networks is critical to wastewater-based epidemiology (WBE) enabling accurate calculation of chemical and pathogen loads within a community. These quantified BCIs, which include genetic material from pathogens as well as pharmaceuticals, from a range of classes, serve as proxies for community-wide health and behaviour patterns. However, a critical knowledge gap exists in understanding how different BCIs move within complex sewer systems, which could lead to misinterpretation of community-level data. This study aims to address this gap by investigating the transport behaviour of 5 common BCIs (carbamazepine, metoprolol, naproxen, venlafaxine and PMMoV) in a real-world gravitational sewer network. In addition, we also spiked the wastewater with deuterated caffeine-d9, allowing discrimination from native caffeine present in the network and therefore, enabling an accurate assessment of recovery due to no public use. Our results revealed that all targets travelled with limited dispersion throughout the first stage of the gravitational sewer, 0.8 km after introduction into the network. It was observed that carbamazepine (logD = 2.8 at sewer pH), exhibited more dispersion throughout the remaining 2.3 km of the gravitational system, showing a broader, more asymmetric trace with increased tailing, which potentially indicates sorption to the solid phase, impacting its movement through the network. All other chemical targets had similar movement patterns, indicating a lower tendency to bind to the solid phase (logD < 1, at average sewer pH). Loads were calculated using dye-predicted flow rates and normalized to caffeine-d9. Carbamazepine loads were under-predicted by 74 %, attributed to losses to the solid phase throughout the sewer system. Conversely, metoprolol, naproxen, and venlafaxine loads were over-predicted (146 %, 32 %, and 129 %, respectively), likely due to additional public inputs. Our results demonstrate that more hydrophilic chemicals move throughout the sewer network with limited dispersion while hydrophobic compounds may experience significant losses. These findings have important implications for the accurate interpretation of WBE data, future BCI tracing studies and the selection of appropriate chemical markers for community health monitoring.

Understanding the fate and turnover of the pools that comprise dissolved organic nitrogen (DON) in soil is key to determining its role in ecosystem functioning. We investigated seasonal changes of dissolved organic carbon (DOC) and nitrogen (DON) concentrations within four molecular weight (MW) size fractions across an altitudinal gradient (from lowland to montane systems), and quantified individual amino acids and amino acid constituents of oligopeptidic-N, as well as nitrate and ammonium. We tested two ideas: first, that DON is more abundant than DIN in low-productivity relative to high-productivity grassland ecosystems; and second, that the abundance of peptides and amino acids is likewise greater in low- than high-productivity grassland. The most productive site had a history of inorganic fertiliser application, and hence in this site alone DIN was more abundant than DON. Plant productivity varied 3-fold between the other sites, and DON was generally at higher concentrations in the sites of lower productivity both in absolute terms as well as relative to DIN, with a large increase observed in spring. The fraction containing the highest concentration of the DON had a MW of >100 kDa, and in summer and autumn this fraction was more abundant at the lowest productivity site. We conclude that relationships between the abundance of DON relative to DIN and ecosystem productivity is dependent on season, and hence more complex than previously suggested, and that peptides are a dynamic and potentially nutritionally significant component of DON.

No abstract is provided for this article.

The adoption of biodegradable plastic mulch films (PMFs) has increased as a sustainable alternative to conventional PMFs. However, evidence suggests that current biodegradability standards may not reflect in-field conditions, leading to potential accumulation of biodegradable PMFs in soil with yet undetermined effects on soil microbial communities. We therefore conducted a field experiment to investigate the above and below ground degradation of one conventional and seven biodegradable PMF blends in a temperate climate (UK) over 12 months. We found that PMFs had no effect on soil properties and a negligible effect on microbial community structure. The main factors driving change in relative abundance of bacteria and fungi were exposure time, followed by the potential of meso- and macrofauna interactions. PMFs buried in soil showed no sign of fragmentation, regardless of presence of meso- and macrofauna, which was likely the cause for no overall difference in microplastic concentrations. The slow degradation of all PMFs combined with the lack of physical fragmentation under natural conditions, indicates that degradation is slower than expected according to current biodegradability standards. This highlights the importance of reframing standards by treating degradation as a system property, influenced by a variety of environmental and intrinsic factors.

Due to climate change, the frequency and duration of flood events are predicted to increase in many regions of the world. This is expected to cause large changes in soil functioning and to a progressive decline in soil quality such as reduced rates of nutrient cycling, enhanced greenhouse gas emissions and loss of soil biodiversity. There is a knowledge gap, however, on how temperate agricultural soils under different management practices (e.g. manure application) respond to prolonged river or coastal flooding. The main objective of this work was to determine the effects of a simulated prolonged flooding with saline and freshwater on soil N cycling, following application of a low C:N organic amendment (broiler litter) at two temperatures, representative of a winter and a spring flood event. Using laboratory mesocosms we simulated prolonged winter (6 °C) and spring (14 °C) flooding of soil amended with broiler litter. We also compared the effects of inundation with either river (freshwater) or coastal (saline) water. An agricultural grassland soil (Eutric Cambisol) was subjected to different combinations of treatments (flood with fresh or saline water, winter vs spring temperatures, with/without poultry manure). The impact of these treatments on soil solution N dynamics, greenhouse gas emissions (CO2, CH4, N2O) and microbial community structure (by PLFA analysis) were evaluated over an 11 week simulated flood event followed by an 8 week soil recovery period (without flood). Overall, potential losses of NH4 + and cumulative GHG emissions were increased by flooding and the presence of manure. CH4 emissions were found to dominate under freshwater flooding conditions and N2O under saline flooding. Significant releases of GHG occurred during both flooding and after floodwater removal. Temperature was less influential on regulating GHG under the different treatments. These releases in GHG were associated with disruption in N cycling and changes in soil microbial composition and these changes persisted after floodwater removal. Extreme flooding negatively impacts soil functioning, however, the magnitude of any changes remain critically dependent on flood duration and source of flood water, and management conditions. Further work is required at the field scale to understand the molecular basis of the responses observed in this study.

Epiphytic orchids rely on the habitat provided by their plant hosts to survive. The naturalisation of Austropuccinia psidii (G. Winter) Beenken (the causal agent for myrtle rust) in Australia means that some of these plant hosts, from the family Myrtaceae, are at risk of serious decline. We aimed to identify orchid species that associate with myrtaceous host plants and determine which, if any, might be susceptible to loss of habitat as a result of myrtle rust. We reviewed species descriptions and herbarium records and identified 73 epiphytic orchid species that are commonly found growing on myrtaceous hosts. At least seven orchid species are predominantly reliant on myrtaceous hosts, are distributed predominantly in the myrtle rust zone, and have host species that are highly or extremely susceptible to myrtle rust. Four of these orchid species are already listed as threatened. The impact of myrtle rust is broader than causing decline of Myrtaceae species, with knock-on effects on other biota, including epiphytic orchids. Moreover, there is the potential for further impact on these orchids through fragmentation (e.g. affecting pollination) and interactive effects with fire. Increased effort is required to identify the relative frequency of myrtaceous and non-myrtaceous hosts for these epiphytic orchid species, especially in relation to the compound effects of myrtle rust and other perturbations, such as fire and climate change. Where this is not possible, ex situ conservation may be required.