Browsing by Subject "denitrification"

Sort by: Order: Results:

Now showing items 1-3 of 3
  • Kabir, Kazi Md. Jahangir (Helsingin yliopisto, 2017)
    Plenty of CO2 is commonly emitted from cultivated peat soils and substantial N2O emissions have occasionally been measured from acid sulphate soils. The factors limiting the emission of CO2 and N2O from the different layers of organic acid sulphate soil in Pärnänsuo were studied by aerobic and anaerobic incubation experiments. Two topsoil peat layers (upper and lower) and two mineral soil layers (upper and lower) were investigated. An aerobic experiment was carried out to see the emission of CO2 and N2O after application of glucose and ammonium, at two different temperatures (5o and 20o C). The water content of the soils was adjusted to 60% water- filled pore space (WFPS). Anaerobic experiment was carried out to assess the denitrification potential of different layers and the effect of glucose and nitrate alone and in combination as at 20oC using the acetylene inhibition technique. The lower peat layer exhibited more CO2 emission comparing to upper peat in the aerobic experiment. Additionally, in both peat layers and upper mineral soil layer, CO2 emission was increased exceedingly after glucose application. In the anaerobic experiment, potential denitrification from the upper peat was significantly higher than from other soil layers. Besides, the soil layers responded differently to C and N application. N2O emission from the upper peat was limited by easily available C whether it was applied as glucose alone or, in the presence of nitrate. On the contrary, N2O emission from lower peat layer was limited by nitrate with or, without glucose, but not by glucose alone. Both upper and lower mineral soil denitrification was limited by nitrate without glucose or, in combined with glucose, and not by glucose alone. Nitrogen mineralization pattern was different in upper and lower peat. A very high amount of NO3- was found in the upper peat, while there was a high amount of NH4+ in lower peat. Both the NO3- and NH4+ showed an increasing trend in lower mineral comparing to upper mineral, depicting an exceedingly high amount of mineral N at deeper layers
  • Tilstra, Arjen; Roth, Florian; El-Khaled, Yusuf C.; Pogoreutz, Claudia; Raedecker, Nils; Voolstra, Christian R.; Wild, Christian (2021)
    Recent research suggests that nitrogen (N) cycling microbes are important for coral holobiont functioning. In particular, coral holobionts may acquire bioavailable N via prokaryotic dinitrogen (N-2) fixation or remove excess N via denitrification activity. However, our understanding of environmental drivers on these processes in hospite remains limited. Employing the strong seasonality of the central Red Sea, this study assessed the effects of environmental parameters on the proportional abundances of N cycling microbes associated with the hard corals Acropora hemprichii and Stylophora pistillata. Specifically, we quantified changes in the relative ratio between nirS and nifH gene copy numbers, as a proxy for seasonal shifts in denitrification and N-2 fixation potential in corals, respectively. In addition, we assessed coral tissue-associated Symbiodiniaceae cell densities and monitored environmental parameters to provide a holobiont and environmental context, respectively. While ratios of nirS to nifH gene copy numbers varied between seasons, they revealed similar seasonal patterns in both coral species, with ratios closely following patterns in environmental nitrate availability. Symbiodiniaceae cell densities aligned with environmental nitrate availability, suggesting that the seasonal shifts in nirS to nifH gene abundance ratios were probably driven by nitrate availability in the coral holobiont. Thereby, our results suggest that N cycling in coral holobionts probably adjusts to environmental conditions by increasing and/or decreasing denitrification and N-2 fixation potential according to environmental nitrate availability. Microbial N cycling may, thus, extenuate the effects of changes in environmental nitrate availability on coral holobionts to support the maintenance of the coral-Symbiodiniaceae symbiosis.
  • Jäntti, Helena; Stange, Florian; Leskinen, Elina; Hietanen, Susanna (2011)
    The Baltic Sea is one of the most eutrophic marine areas in the world. The role of nitrogen as a eutrophicating nutrient in the Baltic Sea has remained controversial, due to lack of understanding of nitrogen cycling in the area. We investigated the seasonal variation in sediment nitrification, denitrification, anaerobic ammonium oxidation (anammox), and dissimilatory nitrate reduction to ammonium (DNRA) at two coastal sites in the Gulf of Finland. In addition to the in situ rates, we assessed the potential for these processes in different seasons. The nitrification and nitrogen removal processes were maximal during the warm summer months, when the sediment organic content was highest. In colder seasons, the in situ rates of the nitrification and nitrate reduction processes decreased, but the potential for nitrification remained equal to or higher than that during the warm months. The denitrification and nitrification rates were usually higher in the accumulation basin, where the organic content of the sediment was higher, but the transportation area, despite lower denitrification rates and potential, typically had higher potential for nitrification than the accumulation basin. Anammox and DNRA were not significant nitrate sinks in any of the seasons sampled. The results also show that the denitrification rates in the coastal Gulf of Finland sediment have decreased, and that benthic denitrification might be a less important sink for fixed nitrogen than previously assumed.