KAVAMURA, V. N.

LANÇONI, M. D.

MELO, I. S. de

TAKETANI, R. G.

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,~~.~P4.32 Archaeal ammonium-oxidizers and nirS-type denitrifiers dominate the \~rhizosphere of leguminous trees in Brazilian semiarid soils212Rodrigo Gouvêa Taketani, Milena Duarte Lonçoni, Vanessa Nessner Kavamuraand Itamar Soares de MeIoLaboratory of Environmental Microbiology, EMBRAPA Environment, Jaguariúna-SP,Rodovia SP340 km 127,5, CEP13820-000, BrazilCorresponding mail: RodrigoGouvêaTaketani.rgtaketani@yahoo.com.brThe semi-arid biome known as Caatinga covers 9.8% of the Brazilian territory, with an areaof841.261km2. In this region the annual amount of rain is usually around 500-800 mm vear"irregularly distributed throughout the year. Hence, life in this biome has been selected towithstand long periods of drought (that can last up to 12 months). Another importantcharacteristic of this environment is its critically low nitrogen content due to the high percentageof sand in these soils. These features lead to a dominance of plants that can form interactions withnitrogen fixing microorganisms such as leguminous trees. Hence, the abundance of plant speciesin this environment regardless of this constrains. In this context, the knowledge about themicroorganisms that inhabit this biome is crucial, due to their role on organic matterdecomposition, primary production and nutrient cycling. Therefore, the aim of this study is toevaluate the key microbial guilds that are responsible for the nitrification and denitrification in therhizosphere of the most abundant and widespread leguminous trees in the Brazilian semiaridbiome (the Caatinga). Thus we sampled the rhizosphere of three Mimosa tenuiflora and SenegaJialangsdorffii adult trees (spread over 300 m3 on average) on six different sites and evaluated usingReal-time PCR the amoA of archaea (AOA) and bacteria (AOB), nirS and nirK genes. Theammonium-oxidizing guild was formed mainly by archaea that corresponded to 60% of the totalamoA copy numbers. The AOA and AOB abundance was about 20.0% higher in M. tenuiflorasamples. It could be noticed that there was a spatial effect on the abundance of ammonium-oxidizing communities. Additionally, abundance of nirS genes was more than ten fold that of nirK.As was observed for the AOA and AOB the abundance of denitrifiers was 85% higher in M.tenuiflora. In conclusion, the rhizosphere of two of the most abundant and widespreadleguminous trees in the Brazilian semiarid was dominated by archeal ammonium-oxidizers andnirS type denitrifiers and their abundance was regulated by tree species and sampling site.

Archaeal ammonium-oxidizers and nirS-type denitrifiers dominate the rhizosphere of leguminous trees in Brazilian semiarid soils.

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