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Impact du potentiel matriciel sur la biodégradation de résidus végétaux - Evolution spatio-temporelle de la détritusphère

Abstract : As a result of the heterogeneous spatial distribution of microorganisms and substrates in soil and restricted accessibility, biodegradation occurs mainly in hot-spots, such as in the detritusphere induced by decomposing plant residues. Knowing the characteristics of the volume of soil involved in decomposition of a given organic substrate would help understand and predict biodegradation, while this information is not yet known for given soil characteristics. Our objectives were: (i) to identify the volume of soil involved in the biodegradation of plant residues and (ii) to determine to what extent this volume is affected by soil moisture under diffusive conditions, by monitoring the mineralisation and spatio-temporal evolution of residues-C and microorganisms in soil at the scale of the microbial habitat. We incubated repacked soil cores, with a central layer of 13C labelled maize residues at three different matric potentials. We monitored the 13C and total C mineralisation over 601 days of incubation, we separated soil slices with increasing distances from the residues at 3, 7, 15 and 45 days and analysed therein the 13C from the residue, the microbial community structure and its activity by processing PLFA and 13C-PLFA but also prepared thin sections for fluorescence and nanoSIMS observations. Mineralisation and priming effect increased with soil moisture, but beyond 70 days, they both become higher than expected in dry conditions. A few mm thick detritusphere was established as fast as the soil humidity was important, with an increasing gradient of 13C, total, 13C PLFA and observed colonies towards the residues layer. Most 13C from the residues was located in the first two millimetres of the detritusphere and little impacted by matric potential. The degrading microbial communities were different from the total communities but similar in wet and dry conditions. Both bacteria and fungi were involved in biodegradation after 7 days of incubation. The use of analysis methods of points repartition between them and according to macropores allowed us to obtain little widespread micro-scale data in soil sciences on the distribution of soil microorganisms. The aggregation of microorganisms seems little affected by the water content and the proximity of the residue. On the other hand, distribution gradients of microorganisms around the macropores were stronger in dry than wet conditions and in contact with the residue. The NanoSIMS observations could not give very reliable results but were consistent with a rapid assimilation of the resources available after a few days of incubation. It seems more generally that in the case of dry soil, part of the processes are slower (establishment of the detritusphere, development of fungi, biodegradation, priming effect, distribution of microorganisms around the pores, etc.), however, their intensity is not lessened.
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  • HAL Id : tel-03181169, version 1

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Charlotte Vedere. Impact du potentiel matriciel sur la biodégradation de résidus végétaux - Evolution spatio-temporelle de la détritusphère. Science des sols. Université Paris-Saclay, 2020. Français. ⟨NNT : 2020UPASB014⟩. ⟨tel-03181169⟩

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