International audience

International audience | The effect of wastewater irrigation on the diversity and composition of bacterial communities of soil mesocosms planted with lettuces was studied over an experiment made of five cultivation campaigns. A limited effect of irrigation with either raw or treated wastewater was observed in both alpha-diversity and beta-diversity of soil bacterial communities. However, the irrigation with wastewater fortified with a complex mixture of fourteen relevant chemicals at 10 mu g/L each, including pharmaceutical, biocide, and pesticide active substances, led to a drift in the composition of soil bacterial community. One hundred operational taxonomic units (OTUs) were identified as responsible for changes between treated and fortified wastewater irrigation treatments. Our findings indicate that under a realistic agronomical scenario, the irrigation of vegetables with domestic (treated or raw) wastewater has no effect on soil bacterial communities. Nevertheless, under the worst-case scenario tested here (i.e., wastewater fortified with a mixture of chemicals), non-resilient changes were observed suggesting that continuous/repeated irrigation with wastewater could lead to the accumulation of contaminants in soil and induce changes in bacterial communities with unknown functional consequences.

International audience | In 2020 two main French research institutes, INRA and IRSTEA, merged to form INRAE the French National Research Institute for Agriculture, Food and Environment. This was a timely opportunity to update the ecotoxicology delineations and to identify new key issues to be developedat INRAE, notably by including aquatic ecosystems biodiversity and public policies as new research priorities, and for the French ECOTOX Network of terrestrial and aquatic ecotoxicology supported by INRAE (https://www6.inrae.fr/ecotox/) to address new research and development topics.Within this context, the ecotoxicology of the soil:water continuum (SWC) was chosen as the theme of the 7th seminar of the ECOTOX Network held as a 2-day webinar in November 2020. This special issue proposes a selection of some of the presented studies, covering subjects from terrestrial to aquatic ecotoxicology, including experimental and modelling approaches, to finally tentatively describe what could stand for SWC ecotoxicology in the Anthropocene context.

International audience | The evaluation of soil quality requires the use of robust methods to assess biologically based indicators. Among them, enzyme activities are used for several decades, but there is a clear need to update their measurement methods for routine use, in combining feasibility, accuracy, and reliability. To this end, the platform Biochem-Env optimized a miniaturized method to measure enzyme activities in soils using colorimetric substrates in micro-well plates. The standardization of the method was carried out within the framework of ISO/TC 190/SC 4/WG 4 "Soil quality - Biological methods" workgroup, recommending an inter-laboratory evaluation for the publication of a full ISO standard. That evaluation, managed by the platform, was based on the measurement, in six soils of contrasted physicochemical properties, of the ten soil enzyme activities described in the standard. Eight laboratories were involved in the validation study. Only 2.7% of outliers were identified from the analyses of the whole dataset. The repeatability and reproducibility of the method were determined by computing, respectively, the intra-laboratory (CVr,) and inter-laboratory (CVR) coefficients of variation for each soil and enzyme. The mean CVr ranged from 4.5% (unbuffered phosphatase) to 9.9% (alpha-glucosidase), illustrating a reduced variability of enzyme activities within laboratories. The mean CVR ranged from 13.8% (alkaline phosphatase) to 30.9% (unbuffered phosphatase). Despite this large CVR noticed for unbuffered phosphatase, the method was repeatable, reproducible, and sensitive. It also proved to be applicable for measuring enzyme activities in different types of soils. These results have been found successful by ISO/TC 190/SC4 and resulted in the publication of ISO 20130:2018 standard.

International audience | The implementation of Nature-based Solutions (NBS) in cities has shifted to an integrated approach paradigm, raising the need for a shared, explicit and formal representation of knowledge on NBS in urban water management. A solution is building an ontology: it is a representation that merges data and expert knowledge, prevents miscommunication, handles heterogeneous data types and formats, and can draw inferences. The ontology we present here was focused on describing a water treatment chain (core ontology), classifying NBS (notably Treatment Wetlands (TW)) and treatment mechanisms. Its construction has mobilized expert knowledge, existing ontologies and explicitation of relations between concepts, sometimes from different knowledge domains: technical, geographical, socio-environmental. The ontology is not only for description of NBS in urban water management, but also for better future database structuration and modelling purposes (for predictions in a decision-making support tool). The ontology will improve from iterative expert feedback.

The problematic of microplastics pollution in the marine environment is tightly linked to their colonization by a wide diversity of microorganisms, the so-called plastisphere. The composition of the plastisphere relies on a complex combination of multiple factors including the surrounding environment, the time of incubation along with the polymer type, making it difficult to understand how the biofilm evolves during the microplastic lifetime over the oceans. To better define bacterial community assembly processes on plastics, we performed a 5 months spatio-temporal survey of the plastisphere in an oyster farming area in the Bay of Brest (France). We deployed three types of plastic pellets in two positions in the foreshore and in the water column. Plastic-associated biofilm composition in all these conditions was monitored using 16 S rRNA metabarcoding and compared to free-living and attached bacterial members of seawater. We observed that bacterial families associated to plastic pellets were significantly distinct from the ones found in seawater, with a significant prevalence of filamentous Cyanobacteria on plastics. No convergence towards a unique plastisphere was detected between polymers exposed in the intertidal and subtidal area, emphasizing the central role of the surrounding environment on constantly shaping the plastisphere community diversity. However, we could define a bulk of early-colonizers of marine biofilms such as Alteromonas, Pseudoalteromonas or Vibrio. These early-colonizers could reach high abundances in floating microplastics collected in field-sampling studies, suggesting the plastic-associated biofilms could remain at early development stages across large oceanic scales. Our study raises the hypothesis that most members of the plastisphere, including putative pathogens, could result of opportunistic colonization processes and unlikely long-term transport.

International audience | Some steps of the soil nitrogen (N) cycle are sensitive to environmental pressures like soil moisture or contamination, which are expected to evolve during the next decades. Individual stresses have been well studied, but their combination is not yet documented. In this work, we aimed at assessing the importance of the soil moisture on the impact of copper (Cu) contaminations on the N cycling soil function using the potential nitrification activities (PNA) as bioindicator. A two-step experiment was performed. First, a loamy soil was incubated 5 weeks in either 30, 60, or 90% of its water holding capacity (WHC) or alternating drought and rewetting periods. Thereafter, soil samples were exposed to a gradient of Cu concentrations through a bioassay involving nitrification. The dose-response curves of PNA in function of added Cu were modeled to calculate the effective Cu concentrations, namely ECx with x being the percentage of PNA inhibition. These values were then compared between experimental conditions to highlight differences in threshold values. The preincubation moisture treatments significantly affected the PNA responses to the secondary Cu stress with, for instance, hormetic responses in all cases except for the dry-rewetting treatment. Small PNA inhibitions were estimated for high Cu doses in the soils with low water contents (30% WHC) or submitted to dry-rewetting cycles, contrarily to the patterns observed for the soils with high water contents (90% WHC) or submitted to a single period of drought. Overall, significant differences were found in estimated ECx values between moisture treatments.

International audience | Insects play many important roles in nature due to their diversity, ecological role, and impact on agriculture or human health. They are directly influenced by environmental changes and in particular anthropic activities that constitute an important driver of change in the environmental characteristics. Insects face numerous anthropogenic stressors and have evolved various detoxication mechanisms to survive and/or resist to these compounds. Recent studies highligted the pressure exerted by xenobiotics on insect life-cycle and the important role of insect-associated bacterial microbiota in the insect responses to environmental changes. Stressor exposure can have various impacts on the composition and structure of insect microbiota that in turn may influence insect biology. Moreover, bacterial communities associated with insects can be directly or indirectly involved in detoxification processes with the selection of certain microorganisms capable of degrading xenobiotics. Further studies are needed to assess the role of insect-associated microbiota as key contributor to the xenobiotic metabolism and thus as a driver for insect adaptation to polluted habitats.

International audience | Some steps of the soil nitrogen (N) cycle are sensitive to environmental pressures like soil moisture or contamination, which are expected to evolve during the next decades. Individual stresses have been well studied, but their combination is not yet documented. In this work, we aimed at assessing the importance of the soil moisture on the impact of copper (Cu) contaminations on the N cycling soil function using the potential nitrification activities (PNA) as bioindicator. A two-step experiment was performed. First, a loamy soil was incubated 5 weeks in either 30, 60, or 90% of its water holding capacity (WHC) or alternating drought and rewetting periods. Thereafter, soil samples were exposed to a gradient of Cu concentrations through a bioassay involving nitrification. The dose-response curves of PNA in function of added Cu were modeled to calculate the effective Cu concentrations, namely ECx with x being the percentage of PNA inhibition. These values were then compared between experimental conditions to highlight differences in threshold values. The preincubation moisture treatments significantly affected the PNA responses to the secondary Cu stress with, for instance, hormetic responses in all cases except for the dry-rewetting treatment. Small PNA inhibitions were estimated for high Cu doses in the soils with low water contents (30% WHC) or submitted to dry-rewetting cycles, contrarily to the patterns observed for the soils with high water contents (90% WHC) or submitted to a single period of drought. Overall, significant differences were found in estimated ECx values between moisture treatments.