Publications

Summary Arctic tundra ecosystems contain 14% of the global soil carbon ( C ) store which is becoming vulnerable to decomposition. Arctic soil organic matter ( SOM ) contains large amounts of old, recalcitrant, high molecular weight ( MW ) C compounds which are protected from decomposition whilst soils remain frozen. Climatic change alters soil temperature and water regimes in the Arctic, however, the impact of these changes on C decomposition and storage is poorly understood. We investigated vegetation emergence, microbial dynamics and nutrient fluxes in response to snow melt on the high A rctic S valbard archipelago using field and laboratory studies. Using bacterial and archaeal genetic material (16 S rRNA ) and ammonia‐oxidising genes, microbial communities were quantified in transects across the active snow melt front. The effects of soil temperature and water content on SOM decomposition rates were measured using 14 C ‐labelled low and high MW compounds. Vegetation and below‐ground microbial communities, in the field, responded rapidly with peaks in nutrient availability and soil respiration observed within 72 h of snowmelt. Temperature strongly drives early growing season C dynamics in the A rctic. We suggest the nutrient peaks following snowmelt, coupled with higher levels of DNA in the subniveal zone are due to the decomposition of bacteria and archaea from previous years. We show, in the laboratory, when soils thaw, mineralisation of recalcitrant C (high MW ) compounds was sensitive to soil water but not to increasing temperatures. In contrast, low MW compounds exhibited sensitivity to both temperature and soil water. We suggest that if future soil water content increases under climate change, high MW compounds could become more susceptible to decomposition, releasing more C to the atmosphere.

The value of riparian areas has long been recognised due to their contribution in supporting wildlife diversity and their capacity to deliver a wide range of ecosystem services. Their multiple uses (e.g. flood prevention, biodiversity, pollutant attenuation) combined with an inconsistent use of terminology (e.g. river bank, floodplain, wetland, buffer strip), however, has led to the development of fragmented policies associated with riparian areas. This review brings together current EU and UK legislation alongside research publications focused on riparian areas. We critically evaluate the current legislative framework relating to riparian areas and identify key scientific knowledge gaps which need to be addressed to support future decision-making. Our findings revealed several major problems associated with riparian policy and management, including: (i) the fragmented nature of legislation concerning riparian areas; (ii) the presence of redundant policy instruments, (iii) a lack of practical objectives, (iv) contradictory measures, and (v) unachievable targets. Further, our results suggest that most research is focused on agricultural systems and single ecosystem attributes or functions, rather than supporting an ecosystem-service approach that is widely aspired to in policy statements. We recommend that future research could better support riparian protection policies by focusing less on what the different ecosystems ‘are’, and more on what they can ‘offer’ by way of multiple benefits.

Microplastics (MPs, <5 mm in diameter) have been widely recognized as a critical environmental issue due to their extensive use and low degradation rate. Based on current evidence, our aim is to evaluate whether MPs represent an emerging threat to plant-soil health in agroecosystems. We assess the ecological risks to plant-microbe-soil interactions associated with MPs and discuss the consequences of MPs on soil carbon (C), nutrient cycling, as well as greenhouse gas emissions in agroecosystems. We also identify knowledge gaps and give suggestions for future research. We conclude that MPs can alter a range of key soil biogeochemical processes by changing its properties, forming specific microbial hotspots, resulting in multiple effects on microbial activities and functions. Mixed effects of MPs on plant growth and performance can be explained by the direct toxicity of MPs or the indirect alteration in soil physical structures and microbial communities (i.e. symbiotic arbuscular mycorrhizal fungi). Because of the diverse nature of MPs found in soils, in terms of polymer type, shape and size, we also see differing effects on soil organic matter (SOM) decomposition, nutrient cycling, and greenhouse gases production. Importantly, increased bioavailable C from the decomposition of biodegradable MPs, which enhances microbial and enzymatic activities, potentially accelerates SOM mineralization and increases nutrient competition between plant and microbes. Thus, biodegradable MPs appear to pose a greater risk to plant growth compared to petroleum-based MPs. Although MPs may confer some benefits in agroecosystems (e.g. enhanced soil structure, aeration), it is thought that these will be far outweighed by the potential disbenefits.

Bioplastics (biodegradable plastics) potentially offer an encouraging alternative to conventional (petroleum-based) plastics. In practice, bioplastics inevitably generate a large number of bio-microplastics (bio-MPs, diameter <5 mm) during the degradation progress. However, the impact of bio-MPs on plant and soil health within agroecosystems remains incomplete. Here, a field study was conducted to investigate the effect of two shapes (fiber and powder) of pure polylactic acid (PLA) bio-MPs on oat (Avena sativa L.) and soybean (Glycine max (L.) Merr.) growth and soil health. Our results showed that PLA application at a representative soil loading rate of 0.2% (w/w) had no significant effect on soil enzyme activities, soil physicochemical properties (soil water content, pH, etc.), root characteristics, plant biomass, and crop yield. Thus, we conclude that soil quality, plant health, and ecosystem multifunctionality were not affected by PLA over one growing season (5 months) in the presence of either bio-MP shape (fiber and powder) for either crop species (oat and soybean). Overall, PLA based bio-MPs may not pose a significant threat to agroecosystem functions in the short term (days to months) in the field, thus may provide a viable environmentally benign solution to replace traditional non-biodegradable plastics in agroecosystems.

Background Brachiaria humidicola (Bh) has the ability to produce biological nitrification inhibitors (NIs) and release NIs from the root to the soil. Aims To compare the effects of growing Bh with Brachiaria ruziziensis (Br, which is not able to produce NIs) on soil nitrogen (N) dynamics, N gases and carbon dioxide (CO 2 ) emissions and nitrifiers and denitrifiers following sheep urine application, a laboratory incubation was conducted in a He/O 2 continuous flow denitrification system (DENIS). This incubation was conducted in the absence of light. Hence the measured effects of Bh and Br on N cycling were the residual effect of biological NIs released into the soil prior to the incubation and released via root death. Methods The treatments were: (1) Bh with water application (Bh + W); (2) Bh with sheep urine (Bh + U); (3) Br with water application (Br + W); (4) Br with sheep urine (Br + U). Results Results showed that soil NO 3 – concentration increased significantly in the soil with sheep urine application after the incubation. Soil nitrous oxide (N 2 O) and nitric oxide (NO) emissions increased immediately after the sheep urine application and peaked twice during the incubation. Cumulative emissions for the first peak were significantly lower from the Bh + U treatment (0.054 kg N ha –1 ) compared with the Br + U treatment (0.111 kg N ha –1 ), but no significant differences were observed in the total cumulative N 2 O and NO emissions between the Bh + U and Br + U treatment at the end of the incubation. Sheep urine addition did not affect the AOA, nirS and nosZ gene copies, but significantly increased the AOB gene copies after the incubation. Conclusions We conclude that the residual effect of Bh to mitigate N 2 O emissions in a highly nitrifying soil is short‐lived.

There is increasing interest and use of nitrification inhibitors (NI) in agroecosystems, yet little is known of their fate in planta. Residues of the organic, N-rich NI, dicyandiamide (DCD), have been found in milk products following commercial application to pasture. We investigated whether plant acquisition and metabolism of DCD were consistent with plant-mediated transmission from soil to agricultural food products. Uptake rates, translocation to the shoot, degradation of the label within wheat tissue and availability within two soils of DCD and the structurally similar naturally occurring N-rich molecule, guanidine, were measured using 14C labelling. Under sterile conditions, over 2 h wheat took up (34 and 14 μmol g−1 root DW h−1 at 1 mM: DCD and guanidine, respectively), translocated (7–15 and 19–22 %) and metabolised (0.4 and 0.9 % of uptake) DCD- and guanidine-14C. Both molecules were also acquired from soil by wheat despite concurrent soil sorption and microbial uptake. Both DCD and guanidine can be acquired and metabolised by graminaceous plants. Although probably not a significant route of N acquisition, plant uptake provides a direct route of DCD entry into the food chain.

Antimicrobial resistance (AMR) is a major public health concern. Antimicrobial residues enter wastewater where their continued presence can lead to an increased risk of AMR while also causing environmental harm when untreated wastewater is discharged into the environment. This research presents the antimicrobial residue surveillance results of a national-scale wastewater sampling campaign across Wales. Wastewater from 15 sites-effluent from 7 hospitals and influent from 8 community wastewater treatment plants-was collected for 5 consecutive days monthly from May-July 2023. This campaign captured more than 30 % of the Welsh population and over 30 % of the population receiving care as hospital inpatients. Using a quantitative approach, over 175 unique wastewater samples were analyzed by ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) for more than 40 antimicrobials including: β-lactams, macrolides, quinolones, sulfonamides, a veterinary antibiotic, an antifungal, antivirals, and numerous metabolites. The most prevalent antimicrobials were clarithromycin, its metabolite N-desmethyl clarithromycin, fluconazole, and trimethoprim as they were detected in all samples. Sulfamethoxazole concentrations ranged from 724-28031 ng/L and trimethoprim ranged from 785-44539 ng/L in hospital effluent-concentrations significantly higher than those reported in published literature. In hospital wastewater, many antimicrobials were present at concentrations which were orders of magnitude higher than their respective predicted no-effect concentrations (PNECs) for antibiotic resistance selection (e.g., metronidazole, trimethoprim). These concentrations create a selective pressure which can drive AMR emergence. Furthermore, some antimicrobials remained at high-risk concentrations even after dilution in community wastewater (e.g., ciprofloxacin, clarithromycin). Environmental risk assessments also identified clarithromycin and ciprofloxacin as agents of concern while vancomycin posed the highest environmental risk (concentrations ca. 1000-38000-fold > PNEC in hospital effluent) should this wastewater enter the environment untreated (e.g., combined sewer overflows). Instances of direct disposal of antimicrobials were clearly identified in hospital wastewater. These results demonstrate the importance of regular monitoring of AMR and potential environmental risk posed by antimicrobials in wastewater, while demonstrating the need for comprehensive national action (e.g., treatment of hospital wastewater on-site, tertiary/quaternary treatment of community wastewater, tailored stewardship programs, focussed control efforts on high-risk antimicrobials) to minimize risks to public health and the environment.

Identifying and halting the decline of High Nature Value farmland (HNV) is seen as essential to the EU meeting its 2020 biodiversity targets. Data on HNV farmland is used to target policy instruments and monitor changes in HNV to assess policy impact and development. Initial estimates of HNV land were based on land cover data with limited spatial resolution. The EU has since taken a distributed approach, allowing countries to develop their own data and metrics to report on the presence of HNV land, and changes to it. Land cover type has been the main data used for reporting but no consistent set of data metrics have been agreed. Therefore, there is interest in both developing standardised reporting metrics and identifying land with high restoration potential to increase the area of HNV land. We explore the relationship between soil associations and broad habitats across a member state (Wales) to determine if any discernible patterns exist between soil and habitat diversity and if soils information might be useful for identifying areas with high restoration potential. We developed a set of criteria to identify soil abundance, combining soil diversity with ecological rare species approaches. The rare (<1000ha) and occasional (1000–10,000ha) soils identified were associated with significantly higher levels of habitat diversity than the national average. We propose that soil diversity information could supplement habitat information in identifying areas of potential restoration interest. Two iconic areas of Wales, the Llŷn Peninsula and Conwy Valley, were compared for restoration potential. Soil diversity in both areas is higher than the national average; habitat diversity was average, or lower in the case of the Llŷn Peninsula. These areas with higher soil diversity offer greater potential for restoration to type-2 HNV. Soil diversity and habitat diversity were found to be positively correlated at a national level despite major management modification of habitats. Given this relationship it is proposed that soil diversity information offers useful metrics alongside land cover data for identifying or comparing areas with regard to potential restoration for HNV.

Grasslands (natural, semi-natural and improved) occupy approximately one-third of the terrestrial biosphere and are key for global ecosystem service provision, storing up to 30% of soil organic carbon (SOC). To date, most research on soil carbon (C) sequestration has focused on croplands where the levels of native soil organic matter (SOM) are typically low and significant potential exists to replenish SOM stocks. However, with the renewed push to achieve "net zero" C emissions by 2050, grasslands may offer an additional C store, utilising tools such as biochar. Here, we critically evaluate the potential for biochar as a technology for increasing grassland C stocks, identifying a number of practical, economic, social and legislative challenges that need to be addressed before the widescale adoption of biochar may be achieved. We critically assess the current knowledge within the field of grassland biochar research in the context of ecosystem service provision and provide opinions on the applicability of biochar as an amendment to different types of grassland (improved, semi-improved and unimproved) and the potential effect on ecosystem provision using a range of application techniques in the topsoil and subsoil. We concluded that the key question remains, is it possible for managed grasslands to store more C, without causing a loss in additional ecosystem services? To address this question future research must take a more multidisciplinary and holistic approach when evaluating the potential role of biochar at sequestering C in grasslands to mitigate climate change.The online version contains supplementary material available at 10.1007/s42773-023-00232-y.

The extent to which long-term application of mineral fertilizers regulates the quantity, quality, and stability of soil organic matter (SOM) in soil matrices remains unclear. By combining four biomarkers, i.e., free and bound lipids, lignin phenols and amino sugars, we characterized the molecular composition, decomposition and origins of SOM in response to 10-year fertilization (400 kg N ha−1 yr−1, 120 kg P ha−1 yr−1 and 50 kg K ha−1 yr−1) in a cropland in North China. We focused on two contrasting fractions: particulate organic matter (POM), and mineral-associated organic matter (MAOM). Fertilization increased soil organic carbon (SOC) by 23% in MAOM, and altered its composition and origins, despite having a limited effect on bulk SOC levels. Fertilization increased plant-derived terpenoids by 46% in POM and long-chain lipids (≥C20) by 116% in MAOM but decreased short-chain lipids (<C20) by 54% in the former fraction. Fertilization reduced suberin-derived lipids by 56% in POM and 30% in MAOM but increased lignin-derived phenols by 74% in POM and 31% in MAOM, implying that crop residues were preferentially stored via the POM form. Fertilization decreased the contribution of microbial residues to SOC in both the fractions. Overall, mineral fertilizers tended to reduce certain labile components within POM (e.g., short-chain lipids), leading to the accrual of recalcitrant molecules (e.g., long-chain lipids, cutin-derived lipids, and lignin-derived phenols) in the MAOM fraction. Collectively, our study suggests that mineral fertilizers can increase SOM stability and persistence by modifying their molecular composition and preservation in the mineral-organic associations in a temperate agroecosystem.