Poster #A (not eligible for poster prize)

Nitrogen cycle in a native tropical montane forest vs. an exotic pine plantation
ARIADNA MATILDE QUINTERO MUÑOZ, ERIKA BUSCARDO , LASZLO NAGY
Department of Animal Biology, University of Campinas, Campinas, São Paulo, Brazil

Soil microbiota has an important ecological role in nutrient cycling. We quantified how substitution of Araucaria angustifolia , an endemic conifer, by Pinus taeda plantation altered the N cycle in a Neotropical montane forest. Microbial biomass (C, N) and genes associated with N cycle were quantified twice a year to capture seasonal differences. There were significant differences in microbial biomass and gene composition between bacteria and archaea with season and conifer species. Araucaria had significantly higher microbial biomass than pine and this was more accentuated in the organic layer than in the mineral topsoil. The patterns were consistent across seasons. The highest abundance of  nifH was found in the pine mineral layer, in correspondence with the lowest [NH4+]. The amoA gene abundances of ammonium-oxidizing archaea and ammonium-oxidizing bacteria were negatively correlated with [NH4+]. The plantation showed higher abundance of bacteria and archaea amoA genes when compared to the araucaria forest. In the plantation, the nifH and archaea amoA genes were found in greater abundances in the mineral soil than in the organic layer. The results show how an exotic and invasive species can affect biogeochemical cycling with potential cascade consequences on ecosystem functions and services.