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Master Thesis

The role of earthworms in the biological processes of the phosphorus cycle

Abstract : Earthworms are soil engineers that are responsible for many ecosystem services such as nutrient availability. Our study will focus on the role of earthworms in the phosphorus (P) cycle to understand their impact on P pools and the processes involved. To do so, a partnership with the Ecotron (CNRS) was put in place. It was organized in 3 different macrocosms treatments: no earthworms, endogeic or anecic earthworms (100g/m2). Bulk soil and casts composites were sampled. Fresh casts were obtained by incubation. The size of P pools was analyzed (by a sequential extraction) as well as the speciation of organic P (by HPIC). The mechanisms were analyzed by a dosage of phosphatase, chemical and biological parameters as well as with the 18O-P ratio. Our results showed that soil digestion increased both available and stable pools and that pool-changes were not stable with cast- aging. Our global approach showed that increases were only visible for resin-extractable P and organic P. Resin-extractable P was increased in fresh cast due to a phosphatase activity visible by 18OP ratios. It was even higher in old casts due to its liberation from microorganisms after their death. Organic P was either increased by selective ingestion by earthworms or by the synthesis and release by microorganisms. The speciation of the organic P suggested that microbes were more active in fresh casts (more ATP and citrate) but not in old casts (no ATP, more AMP and pyrophosphate) that were colonized by fungi (more oxalate, malate, malonate, G6P). There was no difference for phytate and fructose.
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Master Thesis
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Juliette Steculorum. The role of earthworms in the biological processes of the phosphorus cycle. Life Sciences [q-bio]. 2019. ⟨dumas-02747211⟩

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