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Microbial nitrogen dynamics in organic and mineral soil horizons along a latitudinal transect in western Siberia
Author(s) -
Wild Birgit,
Schnecker Jörg,
Knoltsch Anna,
Takriti Mounir,
Mooshammer Maria,
Gentsch Norman,
Mikutta Robert,
Alves Ricardo J. Eloy,
Gittel Antje,
Lashchinskiy Nikolay,
Richter Andreas
Publication year - 2015
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1002/2015gb005084
Subject(s) - mineralization (soil science) , nitrogen cycle , topsoil , nitrification , subsoil , environmental chemistry , tundra , ecosystem , transect , soil organic matter , bulk soil , organic matter , chemistry , ecology , environmental science , soil water , soil science , nitrogen , biology , organic chemistry
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.