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Microbial nitrogen dynamics in organic and mineral soil horizons along a latitudinal transect in western Siberia

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  • Birgit Wild
  • Jörg Schnecker
  • Anna Knoltsch
  • Mounir Takriti
  • Maria Mooshammer
  • Norman Gentsch
  • Robert Mikutta
  • Ricardo J Eloy Alves
  • Antje Gittel
  • Nikolay Lashchinskiy
  • Andreas Richter
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<mark>Journal publication date</mark>05/2015
<mark>Journal</mark>Global Biogeochemical Cycles
Issue number5
Volume29
Number of pages16
Pages (from-to)567-582
Publication StatusPublished
Early online date9/04/15
<mark>Original language</mark>English

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 using (15)N 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.\n\nKEY POINTS: 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.