title: Microbial nitrogen dynamics in organic and mineral soil horizons along a latitudinal transect in western Siberia.
abstract: Soil N availability is constrained by the breakdown of N-containing polymers such as proteins to oligopeptides and amino acids that can be taken up by plants and microorganisms. Excess N is released from microbial cells as ammonium (N mineralization), which in turn can serve as substrate for nitrification. According to stoichiometric theory, N mineralization and nitrification are expected to increase in relation to protein depolymerization with decreasing N limitation, and thus from higher to lower latitudes and from topsoils to subsoils. To test these hypotheses, we compared gross rates of protein depolymerization, N mineralization and nitrification (determined using15N pool dilution assays) in organic topsoil, mineral topsoil, and mineral subsoil of seven ecosystems along a latitudinal transect in western Siberia, from tundra (67°N) to steppe (54°N). The investigated ecosystems differed strongly in N transformation rates, with highest protein depolymerization and N mineralization rates in middle and southern taiga. All N transformation rates decreased with soil depth following the decrease in organic matter content. Related to protein depolymerization, N mineralization and nitrification were significantly higher in mineral than in organic horizons, supporting a decrease in microbial N limitation with depth. In contrast, we did not find indications for a decrease in microbial N limitation from arctic to temperate ecosystems along the transect. Our findings thus challenge the perception of ubiquitous N limitation at high latitudes, but suggest a transition from N to C limitation of microorganisms with soil depth, even in high-latitude systems such as tundra and boreal forest.
  
  
  CONCLUSIONS
  We compared soil N dynamics of seven ecosystems along a latitudinal transectShifts in N dynamics suggest a decrease in microbial N limitation with depthWe found no decrease in microbial N limitation from arctic to temperate zones.
authors.affiliation: Department of Microbiology and Ecosystem Science, University of Vienna Vienna, Austria ; Austrian Polar Research Institute Vienna, Austria ; Department of Earth Sciences, University of Gothenburg Gothenburg, Sweden.
authors.forename: Birgit
authors.initials: B
authors.lastname: Wild
authors.affiliation: Department of Microbiology and Ecosystem Science, University of Vienna Vienna, Austria ; Austrian Polar Research Institute Vienna, Austria.
authors.forename: Jörg
authors.initials: J
authors.lastname: Schnecker
authors.affiliation: Department of Microbiology and Ecosystem Science, University of Vienna Vienna, Austria ; Austrian Polar Research Institute Vienna, Austria.
authors.forename: Anna
authors.initials: A
authors.lastname: Knoltsch
authors.affiliation: Department of Microbiology and Ecosystem Science, University of Vienna Vienna, Austria ; Austrian Polar Research Institute Vienna, Austria.
authors.forename: Mounir
authors.initials: M
authors.lastname: Takriti
authors.affiliation: Department of Microbiology and Ecosystem Science, University of Vienna Vienna, Austria.
authors.forename: Maria
authors.initials: M
authors.lastname: Mooshammer
authors.affiliation: Institute of Soil Science, Leibniz Universität Hannover Hannover, Germany.
authors.forename: Norman
authors.initials: N
authors.lastname: Gentsch
authors.affiliation: Institute of Soil Science, Leibniz Universität Hannover Hannover, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Mikutta
authors.affiliation: Austrian Polar Research Institute Vienna, Austria ; Department of Ecogenomics and Systems Biology, University of Vienna Vienna, Austria.
authors.forename: Ricardo J Eloy
authors.initials: RJ
authors.lastname: Alves
authors.affiliation: Department of Biology, Centre for Geobiology, University of Bergen Bergen, Norway ; Department of Bioscience, Center for Geomicrobiology Aarhus, Denmark.
authors.forename: Antje
authors.initials: A
authors.lastname: Gittel
authors.affiliation: Central Siberian Botanical Garden, Siberian Branch of Russian Academy of Sciences Novosibirsk, Russia.
authors.forename: Nikolay
authors.initials: N
authors.lastname: Lashchinskiy
authors.affiliation: Department of Microbiology and Ecosystem Science, University of Vienna Vienna, Austria ; Austrian Polar Research Institute Vienna, Austria.
authors.forename: Andreas
authors.initials: A
authors.lastname: Richter
keywords: boreal forest; permafrost; protein depolymerization; tundra