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Biodisponibilité du cuivre et du zinc pour les plantes et les vers de terre : interactions entre les effets de fertilisants organiques sur le long-terme et des organismes sur l'évolution des propriétés physico-chimiques du sol

Abstract : The agronomic valorization of organic fertilizers (OF) is one of the main source contamination of agricultural soils in trace elements. This is particularly significant for copper (Cu) and zinc (Zn) for which the ecotoxicity and more generally their impact on soil fertility on the long-term is a matter of concerns. The scientific literature of the two last decades did not enable to state clearly whether Cu and Zn bioavailability for soil organisms will be impacted by OF application. Indeed, previous studies did not take into account the modifications of Cu and Zn availability in soils induced by (i) pH and organic matter (OM) temporal evolution observed with OF application and (ii) organism activities in the soil they can bio-influence. My PhD work thus aimed at assessing the respective effects of soil contamination, soil pH and OM evolution and key soil organisms (i.e. plants and earthworms) in the bio-influenced volume of soil, on Cu and Zn bioavailability for these organisms in the context of OF applications.This work was based on soils sampled from field trials in Réunion and amended for a decade with mineral or organic fertilizers, or never fertilized. The evolution of pH, concentration and aromaticity of dissolved organic matter (DOM), and Cu and Zn availability (i.e. totale concentration and free ionic activity) was measured in soil solutions of the non-bio-influenced soils and the soil bio-influenced by the activities of either plant roots (i.e. rhizosphere) or earthworm bioturbation (i.e. drilosphere). Copper and Zn bioavailability was assessed by the measurement of Cu and Zn concentration in a tropical epi-endogeic earthworm species (Dichogaster saliens) and a temperate plant species (Festuca arundinacea, fescue) exposed to soils in mesocosms under laboratory conditions.In the absence of bio-influence, OF application did not only increase the level of Cu and Zn contamination in soils, but also pH and the concentration and aromaticity of DOM in soil solutions. Total Cu concentration in soil solution increased in soils amended with OF proportionally to DOM concentration while Cu2+ activity decreased mainly proportionally to pH increase, which resulted in a similar Cu availability between soils amended with OF or not. Due to the lower affinity of Zn for DOM, total Zn concentration and Zn2+ activity decreased in soils with OF application proportionally to pH increase, which resulted in Zn availability equal or lower in soils amended with OF than in non-amended soils. Thus, the modification of pH and DOM seems to regulate Cu and Zn availability in non-bio-influenced soils by exerting a protective effect that counteracts Cu and Zn contamination.Under the influence of earthworms or plants, the variation range of pH and DOM concentration was reduced regardless of fertilization type in bio-influenced soils compared to non-bio-influenced soils. In the drilosphere, this resulted in a similar effect of OF application on Cu and Zn availability but in a lesser extent than the effect of OF application in non-bio-influenced soils. In the rhizosphere, the intense root activities resulted in the absence of OF effect on Cu and Zn availability. The combination of the protective effects induced by OF application and organism activity explained why Cu and Zn bioavailability for earthworms and plants did not increase with OF application for a decade despite Cu and Zn contamination in soil.
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Céline Laurent. Biodisponibilité du cuivre et du zinc pour les plantes et les vers de terre : interactions entre les effets de fertilisants organiques sur le long-terme et des organismes sur l'évolution des propriétés physico-chimiques du sol. Ecologie, Environnement. Université Paris Saclay (COmUE), 2019. Français. ⟨NNT : 2019SACLA034⟩. ⟨tel-03276302⟩

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