Dynamique des communautés lombriciennes dans les parcelles conduites en Agriculture Biologique. Modélisation de la dynamique des populations d'Aporrectodea caliginosa.

Abstract : The earthworms fulfil, in the agroecosystems, many services, crucial for the production and proper functioning of the soil. Therefore, it is necessary to deepen our understanding of the drivers of the changes with time of the density and the specific diversity of earthworms communities. Indeed such a knowledge is necessary to predict the effects of the agricultural practices on soil macrofauna and to design cropping systems in organic farming, beneficial to the earthworm abundance. The purpose of this PhD thesis was to analyse, in agricultural fields, the annual variations of the earthworm abundances in the organic farming context of Northern France. We focused on endogeics species, whose abundance was measured during two years (2009 and 2010) in five cropped fields. A model, simulating the earthworm population dynamics of the most abundant species in our cropped fields, A. caliginosa was parametrised with the data collected in thosse fields (and the bibliography). It was also inspired by Pelosi's model (Pelosi et al., 2008). The analysis of the populations dynamics showed a general scheme describing the annual evolution of the abundance (i.e. active endogeic earthworms in the 0-30 cm layer) of these ploughed fields, cropped with cereals. This scheme is characterized by a four-step evolution. a decrease in the abundance (or a stability) at the end of the spring, followed by a summer period with a stability of the population, before an increase at fall, where the abundance reached a higher level compared to the end of spring. Lastly, in winter, the abundance decreases again. This study, which confirmed the general data given by the literature, revealed also significant variations from one year to the other, between A. caliginosa and A. rosea, and also as a function of the crop field. The causes of these variations are discussed in this PhD thesis. Among the possible causes of these variations, soil tillage, especially ploughing, played an important role. This led us to carry out an experiment to study the effects of this practice on the population dynamics of the two endogeic species mentionned above. The results obtained suggested that the effects of the ploughing was species dependent. A. caliginosa was more sensitive than A. rosea, whose abundances were not systematically affected by the ploughing. Those of A. caliginosa were reduced immediately after ploughing in 2009, with some delay (about two months) after this operation. These results emphasize the necessity to study the effect of the agricultural practices through their impact on population dynamics (and not only through the average level of abundance). The third part of our work was devoted to the improvement of the model Wormdyn. We first adapted the model to the species A. caliginosa based on a literature review to determine the the life cycle parameter values for this species. A function describing the effect of density dependence on the abundance was also introduced in the model. The model correctly simulated the average abundances measured in the cropped fields, despite a general tendency to overestimate the abundances, when environmental conditions are favorable. This was only partially corrected by the addition of the density dependence function. The model has to be improved by the introduction of the effect of other factors, first and foremost the quality and quantity of trophic resources.
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Tatiana de Oliveira. Dynamique des communautés lombriciennes dans les parcelles conduites en Agriculture Biologique. Modélisation de la dynamique des populations d'Aporrectodea caliginosa.. Biologie animale. AgroParisTech, 2012. Français. ⟨NNT : 2012AGPT0044⟩. ⟨pastel-00944744⟩

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