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sur le développement des zones arides et semi-arides

Titre : EFECTO DE MIMOSA LUISANA (LEGUMINOSAE) Y DE LAS COSTRAS BIOLOGICAS SOBRE LA DINAMICA DEL CARBONO Y DEL NITROGENO EN EL SUELO DE UN ECOSISTEMA SEMIARIDO EN MEXICO

Auteur : SANDOVAL PEREZ ANA LIDIA

Université de soutenance : Universidad Autónoma Metropolitana (UAM)

Grade : Maestra en Biologia 2011

Résumé
In the semi-arid Valley of Tehuacán-Cuicatlán, Mimosa luisana Brandegee (Leguminosae) creates resource islands (RI) ; however, its association with biological soil crusts (BSC) has not been studied. Soil carbon (C) and nitrogen (N) availability and transformation were determined ; as well as the influence of M. luisana-RI on the cover and richness of the BSC components, in seven plots, located at the Valley of Zapotitlán Salinas, Puebla. In each plot, the soil under the BSC was collected (0-3 cm), in three microenvironments : i) BSC associated with M. luisana-RI (BSC-RI), ii) BSC outside RI (BSC-ORI), and iii) Open areas (OA), 63 samples of BSC-RI and 63 BSC-ORI, during both dry and rainy seasons. Total, available, microbial and mineralization of C and N were determined, as well as nitrification by standard methods. BSC components were quantified (cover) by the point sampling method and taxonomically identified. Data were subjected to an analysis of variance with repeated measures (RMANOVA, p≤0.05) with one factor between groups (BSC-RI, BSC-ORI and OA), and one factor within groups (two seasons). The results show that labile C, Ntotal, microbial N and C mineralization potential of soil concentrations were significantly higher in BSC-RI, intermediate in BSC-ORI and lower in OA. The highest soil organic carbon (SOC) concentration was reported in BSC-RI and BSC-ORI, coinciding with a high C and microbial N concentrations, as well as a high potential C mineralization, suggesting that C availability increased microbial biomass and activity, thus nutrient availability in the soil of these two microenvironments. For both seasons, mosses cover was significantly higher in BSC-RI (37- 42 %) than in BSC-ORI ; in the latter, lichens were the dominant organisms (39-47 %). In contrast, cyanobacteria cover did not vary between BSC-RI and BSC-ORI, neither season. In addition, BSC-RI and BSC-ORI microenvironments showed a higher species dissimilarity composition during the rainy season (95 %) than during the dry season, where similarity was low (42 %). This study demonstrated a positive effect of M luisana-RI and BSC-ORI on the microbial processes that determine C and N soil availability and transformation, being possible to consider BSC-ORI as soil “micro-resource islands” within this ecosystem.

Mots clés : biogeochemistry, biological crust, Mimosa luisana, nutrients, semi-arid ecosystem.

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