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

• Main Authors: Wild, Birgit, Schnecker, Jörg, Knoltsch, Anna, Takriti, Mounir, Mooshammer, Maria, Gentsch, Norman, Mikutta, Robert, Alves, Ricardo J. Eloy, Gittel, Antje, Lashchinskiy, Nikolay, Richter, Andreas
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Washington : Amer Geophysical Union 2015
• Subjects: tundra; permafrost; boreal forest; protein depolymerization; arctic tundra; terrestrial ecosystems; carbon availability; forest ecosystems; alaskan tundra; use efficiency; plant-growth; n uptake; matter; Dewey Decimal Classification500 | Naturwissenschaften; Dewey Decimal Classification500 | Naturwissenschaften570 | Biowissenschaften, Biologie; Dewey Decimal Classification500 | Naturwissenschaften540 | Chemie; Arctic; Dewey; taiga; Tundra; Siberia
• Online Access: https://dx.doi.org/10.15488/483; http://www.repo.uni-hannover.de/handle/123456789/507

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 N-15 pool dilution assays) in organic topsoil, mineral topsoil, and mineral subsoil of seven ecosystems along a latitudinal transect in western Siberia, from tundra (67 degrees N) to steppe (54 degrees 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.