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Accueil du site → Doctorat → États-Unis → 2008 → Diversity, distribution patterns and effect of N fertilization on fungal communities in a semiarid grassland

UNIVERSITY OF NEW MEXICO (2008)

Diversity, distribution patterns and effect of N fertilization on fungal communities in a semiarid grassland

Porras-Alfaro, Andrea

Titre : Diversity, distribution patterns and effect of N fertilization on fungal communities in a semiarid grassland

Auteur : Porras-Alfaro, Andrea

Université de soutenance : UNIVERSITY OF NEW MEXICO

Grade : Doctor of Philosophy (PhD) 2008

Résumé
Semiarid and and ecosystems account for more than one third of the terrestrial ecosystems on Earth. However, only a few studies have sought to characterize the diversity and structure of fungal communities in these ecosystems. A study of the fungal community associated with the roots of dominant grasses, biological soil crust and rhizosphere soils was conducted at long-term nitrogen-enriched experimental plots in a semiarid grassland in New Mexico. Internal Transcribed Spacer (ITS) rDNA sequences in samples collected from 2004 to 2007 were amplified using arbuscular mycorrhizal and fungal specific primers. Arbuscular mycorrhizal fungal (AMF) colonization and diversity were low ; only 7 Operational Taxonomic Units (OTUs) were found, and all are closely related to the ubiquitous Glomus intraradices/fasciculatum group. Abundance of the dominant AMF species was reduced by nitrogen fertilization, but AMF composition in soil and endophytic fungal communities was not affected. In contrast with results obtained with AMF primers, non-specific fungal primers revealed high species richness : approximately 2000 ITS sequences were obtained, with 138 OTUs spanning 23 orders ; 50% of the soil OTUs and 67% of the grama OTUs were novel (less than 97% similarity with respect to sequences in the NCBI database). Rarefaction curves and diversity estimators did not show saturation. Soil and root-associated fungal communities in the semiarid grassland were dominated by dark septate fungi belonging to the Pleosporales with a substantial overlap among rhizosphere and biological soil crust (Jaccard abundance similarity index 0.75). Roots were colonized by at least 10 different orders including endophytic, coprophilous, mycorrhizal, saprophytic, and plant pathogenic fungi. Despite the high diversity found within roots, the root-associated fungal community was dominated by a novel group of dark septate fungi within the order Pleosporales. Possible roles of fungal symbionts in nutrient translocation, adaptation and survival of primary producers (plants and biological soil crust) are discussed.

Mots Clés : Plant biology ; Ecology ; Microbiology ; Soil sciences

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