Browsing by Subject "Nitrification"

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  • Mishra, Anup (Helsingin yliopisto, 2018)
    Tiivistelmä * * Abstract Biochar is a porous carbonaceous solid material produced by pyrolysis, the thermochemical conversion of biomass in anoxic conditions. Various studies suggest that biochar amendment has a postitive effect on soil pH, soil respiration, carbon/ nitrogen ratio, nitrogen mineralization, ammonifcation and nitrification. These measurements have been studied in agricultural systems but are poorly understood in boreal forests. The study was done to investigate the effects of different wood biochar application rates: 0 t ha-1, 5 t ha-1, 10 t ha-1 on soil pH, respiration and nitrogen mineralization. Replicated studies were conducted at field sites located in Juupajoki (61⁰ 48´ N, 24⁰ 18´ E), southern Finland in young pine forest stands. The measurements were taken one year after the addition of biochar. The soil respiration ( CO2 effluxes ) were measured in June and july with different biochar ( pyrolysis temperatures 500⁰ C and 650⁰ C) while N mineralization was measured in November with biochar produced at 650 C. Biochar amendment increased soil pH in plots having biochar 10 t ha-1. Nitrogen mineralization rate in the organic layer increased with the increasing amount of biochar addition but the increase was not statistically significant. The pyrolysis temperature had no significant impact on soil CO2 effluxes. The biochar also did not have any significant impact on soil CO2 effluxes. However, in June, the plots treated with 10 t ha-1 biochar produced at 650⁰ C had significantly higher CO2 effluxes than control plots. The soil respiration data showed that biochar did not have any negative effect on native soil C stocks. We conclude that biochar exhibits important charactertics that will help carbon sequestration and N cycling in boreal forests.
  • Jäntti, Anne Helena; Ward, Bess; Dippner, Joachim; Hietanen, Siru Susanna (2018)
    The redoxclines that form between the oxic and anoxic water layers in the central Baltic Sea are sites of intensive nitrogen cycling. To gain better understanding of nitrification, we measured the biogeochemical properties along with potential nitrification rates and analyzed the assemblages of ammonia oxidizing bacteria and archaea using functional gene microarrays. To estimate nitrification in the entire water column, we constructed a regression model for the nitrification rates and applied it to the conditions prevailing in the area in 2008-2012. The highest ammonia oxidation rates were found in a thin layer at the top of the redoxcline and the rates quickly decreased below detection limit when oxygen was exhausted. This is probably because extensive suboxic layers, which are known to harbor pelagic nitrification, are formed only for short periods after inflows in the Baltic Sea. The nitrification rates were some of the highest measured in the water columns, but the thickness of the layer where conditions were favorable for nitrification, was very small and it remained fairly stable between years. However, the depth of the nitrification layer varied substantially between years, particularly in the eastern Gotland Basin (EGB) due to turbulence in the water column. The ammonia oxidizer communities clustered differently between the eastern and western Gotland Basin (WGB) and the composition of ammonia oxidizing assemblages correlated with the environmental variables. The ammonia oxidizer community composition was more even in the EGB, which may be related to physical instability of the redoxcline that does not allow predominance of a single archetype, whereas in the WGB, where the position of the redoxcline is more constant, the ammonia-oxidizing community was less even. Overall the ammonia oxidizing communities in the Baltic Sea redoxclines were very evenly distributed compared to other marine environments where microarrays have been applied previously. (C) 2018 Elsevier Ltd. All rights reserved.
  • Vetterli, Adrien; Hietanen, Susanna; Leskinen, Elina (2016)
    The diversity and dynamics of ammonia-oxidizing bacteria (AOB) and archaea (AOA) nitrifying communities in the sediments of the eutrophic Gulf of Finland (GoF) were investigated. Using clone libraries of ammonia monooxygenase (amoA) gene fragments and terminal restriction fragment length polymorphism (TRFLP), we found a low richness of both AOB and AOA. The AOB amoA phylogeny matched that of AOB 16S ribosomal genes from the same samples. AOA communities were characterized by strong spatial variation while AOB communities showed notable temporal patterns. At open sea sites, where transient anoxic conditions prevail, richness of both AOA and AOB was lowest and communities were dominated by organisms with gene signatures unique to the GoF. Given the importance of nitrification as a link between the fixation of nitrogen and its removal from aquatic environments, the low diversity of ammonia-oxidizing microbes across the GoF could be of relevance for ecosystem resilience in the face of rapid global environmental changes. (C) 2015 Elsevier Ltd. All rights reserved.