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Poster De Conférence Année : 2018

Effects of a fungicide on oligochaetes and soil organic matter dynamics under controlled conditions

Résumé

Pesticides are used in agriculture to protect crops and ensure satisfying yields. However, they can affect non-target organisms and the related ecological functions (e.g. organic matter decomposition, soil structure). Earthworms (macrofauna > 2 mm in diameter) and enchytraeids (mesofauna < 2 mm and > 0.2 mm in diameter) are Annelida Oligochaeta involved in organic matter transformation. These organisms are considered as ecosystem engineers because they modify environmental conditions for other organisms through their bioturbation activity. For example, Huang and Xia (2018) had shown that earthworm mucus promoted microbial activity that increased organic matter mineralization by specific bacteria. If this process has been quite well studied for earthworms, much less is known about the effects of enchytraeids on soil organic matter dynamics, and even less after pesticide applications. We conducted a laboratory experiment with a natural soil to test the assumption that the application of a commercial formulation of fungicide (Swing® Gold, composed of 50 g.l-1 epoxiconazole and 133 g.l-1 dimoxystrobin) would lead to direct effects on terrestrial Oligochaeta (mortality, weight gain) and indirect effects on organic matter mineralization (CO2 release). We also tested whether these effects were in the same magnitude for earthworms and enchytraeids. For that, we used different concentrations of fungicide (no fungicide, one, and three times the recommended dose RD) and four conditions related to soil fauna (no fauna, earthworms Aporrectodea caliginosa alone, enchytraeids Enchytraeus buchholzi alone, a mix of earthworms and enchytraeids) during 26 days. To estimate the mineralization of organic matter, CO2 release was measured at days 1, 5, 8, 12, 15, 19, 22 and 26. The total mineralization was calculated on the entire experiment duration. For trapping CO2, NaOH was placed in a dish and inserted in each microcosm for 24 hours, then titrated with HCl to determine the CO2 content. No mortality was recorded at the end of the experiment, whatever the treatment. We found no significant effect of the pesticide on animal weight gain. Organic matter mineralization decreased with increasing concentration of pesticide until day 19. After this period, the contrary occurred since the release of CO2 was higher in the treatments with the fungicide at 3 times the RD than in treatments at the RD and without fungicide. This can be explained by some bacteria species which can use pesticides as energy sources, thus enhancing their activities, such as mineralization. Fauna assemblage had no effect on mineralization until day 22. Then, CO2 release was higher when earthworms or enchytraeids were present (no difference between these treatments) than in the treatment without animals. The treatment involving earthworms and enchytraeids had a middle level of mineralization. This could be explained by a competition between earthworms and enchytraeids for food resources. At the end of the experiment, the highest mineralization rate was recorded in the treatment with earthworms and without pesticide. This result confirms the positive role of earthworms in soil organic matter mineralization. We also found an effect of the interaction between the pesticide and fauna treatments on mineralization at days 19 and 22. With no pesticide, enchytraeids were less efficient than earthworms but, probably withstanding higher pesticide contamination, they displayed a higher rate of mineralization than earthworms in conditions with pesticide at 1 and 3 times the RD.
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hal-01811625 , version 1 (02-06-2020)

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Identifiants

  • HAL Id : hal-01811625 , version 1
  • PRODINRA : 431051

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Pauline Thiel, Céline Pelosi, Sylvain Bart, Joël Amossé. Effects of a fungicide on oligochaetes and soil organic matter dynamics under controlled conditions. 13th International Symposium on Enchytraeidae, Jun 2018, Versailles, France. , 2018. ⟨hal-01811625⟩
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