Browsing by Subject "methanogenesis"

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  • Schmidt, Dietrich J. Epp; Kotze, David Johan; Hornung, Erzsebet; Setala, Heikki; Yesilonis, Ian; Szlavecz, Katalin; Dombos, Miklos; Pouyat, Richard; Cilliers, Sarel; Toth, Zsolt; Yarwood, Stephanie A. (2019)
    Urbanization results in the systemic conversion of land-use, driving habitat and biodiversity loss. The "urban convergence hypothesis" posits that urbanization represents a merging of habitat characteristics, in turn driving physiological and functional responses within the biotic community. To test this hypothesis, we sampled five cities (Baltimore, MD, United States; Helsinki and Lahti, Finland; Budapest, Hungary; Potchefstroom, South Africa) across four different biomes. Within each city, we sampled four land-use categories that represented a gradient of increasing disturbance and management (from least intervention to highest disturbance: reference, remnant, turf/lawn, and ruderal). Previously, we used amplicon sequencing that targeted bacteria/archaea (16S rRNA) and fungi (ITS) and reported convergence in the archaeal community. Here, we applied shotgun metagenomic sequencing and QPCR of functional genes to the same soil DNA extracts to test convergence in microbial function. Our results suggest that urban land-use drives changes in gene abundance related to both the soil N and C metabolism. Our updated analysis found taxonomic convergence in both the archaeal and bacterial community (16S amplicon data). Convergence of the archaea was driven by increased abundance of ammonia oxidizing archaea and genes for ammonia oxidation (QPCR and shotgun metagenomics). The proliferation of ammonia-oxidizers under turf and ruderal land-use likely also contributes to the previously documented convergence of soil mineral N pools. We also found a higher relative abundance of methanogens (amplicon sequencing), a higher relative abundance of gene sequences putatively identified as Ni-Fe hydrogenase and nickel uptake (shotgun metagenomics) under urban land-use; and a convergence of gene sequences putatively identified as contributing to the nickel transport function under urban turf sites. High levels of disturbance lead to a higher relative abundance of gene sequences putatively identified as multiple antibiotic resistance protein marA and multidrug efflux pump mexD, but did not lead to an overall convergence in antibiotic resistance gene sequences.
  • Määttä, Tiia (Helsingin yliopisto, 2020)
    Methane (CH4) is a greenhouse gas with a great impact on global climate. In the soil, it is produced in anoxic and consumed in oxic conditions by microbes. Together with different methane transport mechanisms, methane production and consumption directly regulate the resulting soil methane flux. Boreal upland forests are generally considered to act as methane sinks due to high methane consumption. However, some studies have shown a boreal upland forest soil turning from a methane sink to a source after long-term abundant precipitation. This study aimed to examine the effects of soil moisture on CH4 flux from simulated increase in rainfall in a northern boreal upland forest soil, and how simultaneous soil temperature increase, organic litter addition and organic litter and root exclusion affect the temporal changes in flux. The study was conducted in Kenttärova forest in Kittilä, Finland in summer 2018. Split-plot design was used in the experiment with soil moisture being the main treatment variable and soil warming (T), organic litter addition (A) and organic litter and root exclusion (E) subtreatment variables. The design included two main plots: irrigation (I) and control (C), within which each subtreatment was replicated three times. In addition to the T, A and E manipulations, plots without additional manipulations (O) were included for the assessment of the effect of only soil moisture increase, and were replicated four times within both main plots. Methane flux was measured at least once a week using chamber method. Soil moisture and temperature were also continuously measured. The treatment effects were analysed using both autoregressive heterogeneous and autoregressive two-way analyses of variance, TukeyHSD method, variable correlations and Generalized Linear Models. The soil did not turn into a methane source but the results showed significant differences between the irrigation and control site, indicating a strong decreasing effect of soil moisture on soil CH4 sink in all treatment levels. All treatments had lowest uptake rates in August, possibly as a result from highest soil moisture levels. IA treatment was the most effective in producing low uptake rates possibly due to the reduction in gas diffusion. E treatments had contrasting results, IE showing increases in uptake rate by increases in soil moisture but the causes remained unsolved and the results were highly uncertain. T treatment had no effect on uptake likely due to a failure to create soil temperature differences and thus the interactions were not reliably analysed. The results suggest that the changes may have been more related to changes in methane consumption than production. Further research is needed especially for examining the combined effect of litter addition, soil moisture and soil temperature increase on methane flux with multiple temporal replications of the experiment.