Search

The aim of this study was to evaluate the effects of sludge compost (SC) in two rates and pig slurry (PS) on soil quality, in the framework of a field experiment (19-year-old) in a Mediterranean rainfed system. The treatments were compared with mineral fertilization (MF) plus a control treatment (no N fertilization). Soil microstructure and types of voids, earthworm community and its bioturbation were studied using micromorphological methods. Two earthworm species, Koinodrilus roseus and Nicodrilus trapezoides were identified; the latter was not present in the SC treatments. Earthworm abundance and biomass were not affected by fertilization. Pig slurry increased bioturbation associated with earthworm activity, improved soil microstructure (crumb type) and increased the biopore presence (compound packing voids). The control and MF plots showed a platy to massive microstructure with an absence of faunal chambers. In SC plots, non-mixed soil-organic materials were observed and soil vughs were not visible. Composition differences between SC and PS and the total amount of OM applied may have had an impact on the activity and species of earthworms; such changes can be an early indicator of further potential impacts on soil quality however, further contaminant studies are needed to validate this initial assessment. This work was supported by the Spanish Ministry of Economy and Competitiveness and the Spanish National Institute for Agricultural Research and Experimentation (MINECO-INIA) through the projects RTA2013-57-C5-5 and RTA2017-88-C3-3.

International audience; Because earthworms sustain soil functioning and fertility, there is a need to advance the knowledge of their adaptation potential to chemicals in anthropogenic landscapes. Our hypothesis is that there is acclimation to organic chemicals (pesticides) in earthworms that durably persist under conventional farming in anthropogenic landscapes. The adaptation capability of two populations of earthworms (Aporectodea caliginosa) having a different chemical exposure history, - one originating from 20 years of organic farming (naïve population) and another from 20 years of conventional farming (pre-exposed population) - to cope with soil organic pollutant (Opus®, epoxiconazole a worldwide used fungicide) were investigated. Several complementary metabolic and energetic endpoints were followed, and cast production was assessed as a behavioural biomarker related to earthworms ecological role for the soil. Basal metabolism reflected by respiration rate was increased in both fungicide-exposed worms compared to controls. Glycogen resources were decreased in the same proportion in the two populations but more rapidly for the naïve (7 days) than for the pre-exposed population (28 days). Soluble protein and most amino-acids contents increased in the pre-exposed population only, suggesting a detoxification mechanism. Metabolomic profiles showed a cut-off between fungicide-exposed and control groups in the pre-exposed earthworms only, with an increase in most of the metabolites. Exposure to a low dose of epoxiconazole increased cast production of pre-exposed earthworms, and this resulted in an increase in pesticide disappearance. As far as we know, this is the first study which evidenced there is an acclimation to an agricultural chemical in earthworms derived from conventional farming that also relates to a change in their burrowing behaviour, and for which larger consequences for the soil ecosystem need to be addressed. This original finding is of major interest in the frame of ecosystem resilience to global changes. Whether this physiological adaptation is a general pattern of response against fungicides or other pesticides would need to be confirmed with other molecules and agricultural contexts.

I dette arbejde blev der forsket i om langsigtet residualforurening af landbrugsjord fører til pesticidadaptation hos regnorme. Forskningen sigtede også efter at identificere adaptations-omkostningerne fra individ- til populationsniveau, og konsekvenserne for økosystemet. Pesticiders residualforurening blev vurderet og sammenlignet i; tre konventionelt styrede marker (klassificeret efter evaluering af pesticid-anvendelser som ”højt-”, ”medium-”, og ”lav-input”), en mark styret ud fra økologiske betingelser, og et økologisk permanent græsningsareal, alle havde været styret på denne måde i mere end 20 år. Ved hjælp af en vand-ekstraktionsmetode blev 6,8 og 4 pesticidresiduums udvundet i henholdsvis ”høj-”, ”medium-”, og ”lav-input” markerne, og næsten ingen pesticider blev detekteret i jorden fra den økologiske mark bortset fra lave niveauer af resterende (højst sandsynligt 20 år gammelt) atrazin. Regnorms-populationerne Aporrectodea caliginosa og Allolobophora chlorotica blev fundet i alle fem marker, bortset fra A. chlorotica som ikke var til stede i den økologiske mark. Adaptationsstrategier blev undersøgt ved at sammenligne populationerne af disse regnorme de forskellige marker imellem ifølge flere parametre i felt- og laboratoriebedømmelserne. De målte parametre rangerede fra molekylære- (biotransformation og antioxiderende enzymer), biokemiske- (primære energiressourcer), og metaboliske- (respirationsrate, metabolomics) niveauer, til individuelle- (vægt, længde) og populations-relaterede parametre (puppe og juvenile livskarakterer), og til de mulige konsekvenser for økosystemet med hensyn til bioturbation (regnormes grave-adfærd) og nedgang i koncentrationen af ekstraherbare pesticider. Forbedret afgiftnings- og antioxiderende potentiale blev demonstreret langs gradienten af pesticid forurening i felten. Forbedret afgiftning i den pre-eksponerede population var særdeles tydeliggjort ved eksponeringen til pesticider i laboratoriet sammenliget med den økologiske population. Der blev observeret distinkte energibehov og metabolisk omgruppering populationerne imellem, dette var mere udtalt hos de pre-eksponerede regnorme. Der blev detekteret fysiologiske adaptationer hos de pre-eksponerede dyr, og dette hang sammen med en kompensatorisk øgning i grave-adfærd og nedgang i koncentrationen af ekstraherbare pesticider i jorden. Konsekvenser, på populationsniveau, blev bedømt ud fra de to populationers livskarakterer. Brug af pesticider resulterede i vægtnedgang hos de voksne orme i felten og omfordeling af energiressourcer, formodentlig fra reproduktiv til metabolisk funktion. Dette førte til lavere frugtbarhed og udklæknings-succes og kunne til dels forklare de lavere regnorme-densiteter i den pesticid-påvirkede jord., This work investigated if long-term residual contamination of agricultural soils leads to adaptation of earthworm populations to pesticides. It also aimed at identifying the costs of adaptation from the individual to the population level, and the consequences for the ecosystem. Residual contamination by pesticides was assessed and compared in three fields under conventional management (classified after evaluation of pesticide applications as ''high-'', ''medium-'', and ''low-''pesticide input), one field under organic agriculture requirements and one organic permanent pasture, all in this type of management for more than 20 years. Using a water extraction method, as indicative of the amount of bioavailable pesticides 6, 8 and 4 residues of pesticides were recovered in the ''high-'', ''medium-'', and ''low-input'' fields, respectively, and almost no pesticides were detected in the soil of the organic field except for low levels of residual (possibly 20 years old) atrazine. The endogeic species Aporrectodea caliginosa and Allolobophora chlorotica were found in common to the five fields, -except A. chlorotica which was absent from the organic field-, and were used as biological models. Adaptation strategies were investigated by comparing the populations of these earthworms between the different fields according to several endpoints in field and laboratory assessments. The endpoints measured ranged from the molecular (biotransformation and anti-oxidant enzymes), biochemical (main energy resources), and metabolic (respiration rate, metabolomics) levels, to individual (weight, length) and population-related parameters (cocoon and juvenile life traits), and to the possible consequences for the ecosystem in terms of bioturbation (earthworm burrowing behaviour) and pesticide disappearance as an crucial ecosystem service. Enhanced detoxification and anti-oxidant potential was demonstrated along the gradient of contamination in the fields, and in particular comparing the response to an experimental pesticide exposure between the pre-exposed, thus possibly adapted earthworms from the ''high-input'' field-, and the naïve population from the organic field. Distinct energetic demands and metabolic rearrangements were observed between the populations, more pronounced in the pre-exposed earthworms. Physiological adaptation was demonstrated in pre-exposed animals, and this was associated with an increase in burrowing behaviour and pesticide disappearance in the soil. Population-level consequences were assessed in life traits of the two populations. The conventional farming including the use of pesticides decreased the weight of adult worms in the field and resulted in reallocation of energy resources, possibly from reproductive to metabolic function. This led to lower fecundity and hatching success and could partly explain lower earthworm densities in pesticide-impacted soils., Ce travail de thèse a cherché à déterminer si la contamination résiduelle à long terme des sols agricoles par les pesticides induit le développement de mécanismes d’adaptation aux pesticides chez les vers de terre. Il a aussi visé à identifier les coûts potentiels de l’adaptation de l’échelle de l’individu à celle de la population, et les conséquences pour l’écosystème sol. Une contamination résiduelle du sol par les pesticides est mesurée et comparée dans trois champs cultivés en agriculture conventionnelle (classés en fonction de l’historique cultural comme « haut », « moyen » et « bas » niveaux d’intrants), un champ cultivé en agriculture biologique et une prairie permanente biologique, tous dans ce type de management agricole depuis plus de 20 ans. En utilisant une méthode d’extraction des pesticides en milieu aqueux (représentant la fraction « biodisponible » des pesticides), 6, 8 et 4 résidus de pesticides sont détectés dans les champs à « haut », « moyen », et « bas » niveaux d’applications, respectivement, et un seul pesticide dans le sol du champ biologique (un résidu d’atrazine potentiellement vieux de plus de 20 ans). Les deux espèces endogées Allolobophora chlorotica et Aporrectodea caliginosa , communnes dans les sols des 5 champs,- mis à part A. chlorotica qui est absente du champ cultivé en agriculture biologique-, ont servi de modèles biologiques d’étude. Les stratégies d’adaptation aux pesticides sont étudiées en comparant les réponses de ces populations de vers de terre sur le terrain et après des expositions aux pesticides en laboratoire. Les réponses mesurées s’étendent de l’échelle moléculaire (enzymes de biotransformation et du stress oxidatif), biochimique (ressources énergétiques), métabolique (taux de respiration, métabolomique) à l’échelle de l’individu (biomasse, longueur) et de la population (traits de vie des cocons et des juvéniles), et aux possibles conséquences pour l’écosystème sol en termes de bioturbation (creusement et ingestion de sol) et de dissipation des pesticides comme service ecosystémique. Une capacité de détoxification augmentée et un plus grand potentiel anti-oxidant sont observés le long du gradient de contamination du sol et en laboratoire après exposition des vers de terre des champs conventionnel (population « pré-exposée ») et biologique (« naïve) à des pesticides. Des demandes énergétiques et des réarrangements métaboliques différents sont observés dans les deux populations, et sont plus prononcés chez la population pré-exposée. Une adaptation physiologique est démontrée chez les animaux pré-exposés, qui est associée à une ’augmentation de la bioturbation, et en cascade à une dissipation du pesticide dans le sol. Les conséquences au niveau de la population sont étudiées en termes de traits d’histoire de vie des deux populations pré-exposées et naïves. Le management en conventionnel incluant l’utilisation de pesticides semble diminuer le poids des adultes au champ, et implique potentiellement la réallocation des ressources énergétiques, des mécanismes reproductifs vers les processus métaboliques. Ceci aboutit à une diminution de la fécondité et du pourcentage d’éclosion et pourrait être un facteur participant à la diminution des populations de vers de terre dans les champs cultivés avec utilisation de produits phytosanitaires.