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

• Published in: Global Biogeochemical Cycles
• 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: 2015
• Subjects: Arctic; taiga; Tundra; Siberia
• Online Access: https://eprints.lancs.ac.uk/id/eprint/79564/; https://doi.org/10.1002/2015GB005084

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.