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Universidad de Murcia (2015)

Dynamics of carbon in degraded semiarid soils : effects of organic amendments and associated soil microbial communities

Torres Bocero, Irene Florentina

Titre : Dynamics of carbon in degraded semiarid soils : effects of organic amendments and associated soil microbial communities

Dinámica del carbono en suelos degradados de zonas semiáridas : implicación de enmiendas orgánicas y comunidades microbianas asociadas

Auteur : Torres Bocero, Irene Florentina

Université de soutenance : Universidad de Murcia

Grade : Tesis Doctoral 2015

Résumé partiel
Soil plays a highly important role in sustaining life on earth but soil desertification, in arid and semiarid areas, negatively impacts on a significant loss of organic matter, and therefore of organic carbon, which negatively affects the quality and sustainability of the soil. In such degraded soils, it is of vital importance to restore levels of soil organic carbon to sufficient thresholds to maintain its basic functions. For this reason, the aim of this Doctoral Dissertation is to understand the carbon cycling of semiarid soils and the development of strategies for soil restoration. To reach this goal we have focused on the following topics in particular : the ability of this type of soil to respond to exogenous sources of carbon derived from plants ; the role of the microbial community in the degradation of these carbon sources ; and the link between these carbon sources and the biogeochemical cycling of the important elements (C, N and P), with a particular focus on carbon. The general working Hypothesis of this Doctoral Thesis is that the microbial communities in arid and semiarid soils have a limited capacity for processing carbonaceous substrates as a result of the low content of organic matter usually found in these soils. In order to obtain complete information concerning the dynamics of organic carbon and plant-derived organic amendments with respect to the microbial populations associated with processing of this organic matter, we conducted experiments in both controlled laboratory and field conditions. The first part of the thesis (Chapters 1, 2 and 3) was carried out in controlled laboratory conditions using three molecules of varying complexity : glucose, cellulose and lignin. These molecules are an essential part of the natural plant inputs to soil. We used glucose, cellulose and lignin molecules enriched with 13C (a stable isotope of carbon) in order to track the dynamics of these organic materials and the microbial populations involved in their processing in high resolution. In these experiments we applied, among other techniques, those based on the analysis of the isotopic composition of CO2, water-soluble fractions of C and of humic substances and the isotopic composition of fatty acids (PLFA-SIP). These techniques made it possible to thoroughly track the C cycle, evaluating the persistence and mineralisation of C in addition to the microbial populations associated with the dynamics of the added molecules. The second part of the thesis (Chapters 4 and 5) was carried out in the field, which represents a real setting for the study of soil restoration. In Chapter 4, we evaluated the long-term effects of plant-derived organic amendments (fresh and composted pruning waste) and of the applied dose (150 and 300 t ha-1) on the chemical, biochemical and microbiological properties of a semiarid soil.

Mots clés : Carbono Suelos-Análisis Suelos-Erosión Desertificación Regiones áridas Desarrollo sostenible Química orgánica Química agrícola

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Page publiée le 10 novembre 2015, mise à jour le 30 janvier 2019