Effects of inorganic nitrogen on soil CH4 oxidation in Arctic moist soil

Arctic tundra has been reported to be one of the most N-limited ecosystems in the world. For this reason, increase of available N can substantially alter soil microbial communities and their processes. Recently, warming occurs more rapidly in Arctic ecosystems than any other regions in the world, which can accelerate N mineralization in soils. In addition, It has been reported that extreme deposition of N can occur in Arctic ecosystems where over 90% of the annual N deposition were often found within just a few days. Inorganic nitrogens such as NH₄⁺ and NO₃^- are known to regulate soil CH₄ oxidation in temperate ecosystems. For example, NH₄⁺ is widely acknowledged as an inhibitor of CH₄ oxidation while NO₃^- shows diverse responses in temperate forests. However, effects of N on Arctic ecosystems are still elusive. To investigate effects of inorganic N on soil CH₄ oxidation in Arctic moist acidic tundra, we conducted a lab scale incubation experiment with soil samples. The incubations were set up with low concentration (50 ppm) and high concentration (1,000 ppm) of CH₄ to observe the effects on high and low affinity CH4 oxidation, respectively. NH₄⁺ and NO₃^- were added separately with 3 different concentrations (10, 50, 100㎍ N / g dry soil). Under low concentration of CH₄, both NH₄⁺ and NO₃^- inhibited CH₄ oxidation as N concentration increased. However, under the high concentration of CH₄ , NH₄⁺ exhibited no effect or slightly increased CH₄ oxidation while high concentration of NO₃^-(50, 100) inhibited CH₄ oxidataion significantly. We also conducted DNA based T-RFLP to determine the change in community structure of methanotrophs. Community structure of methanotrophs in N treated soils differed from that of control, suggesting that increased inorganic nitrogen alter the community structure of CH₄ oxidizing bacteria and CH₄ oxidation rate.