Temperature responses of nitrogen processes cannot be inferred from carbon turnover in a boreal Norway spruce forest

• Published in: Journal of plant nutrition and soil science Vol. 182; no. 6; pp. 934 - 944
• Main Authors: Herrmann, Anke M., Coucheney, Elsa
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.12.2019
• Subjects: Boreal forests; Carbon; Cold season; Coniferous forests; Decomposition; Decoupling; Ecosystems; Environmental changes; Fertilization; Forest ecosystems; Forests; Freezing; Freezing point; gross N immobilization; gross N mineralization; Immobilization; Low temperature; Markvetenskap; Melting points; Mineralization; Nitrogen; Pine trees; soil organic matter; Soil Science; Soil temperature; Soils; Taiga; Temperature; temperature sensitivity; Terrestrial ecosystems; winter period
• ISSN: 1436-8730; 1522-2624; 1522-2624
• DOI: 10.1002/jpln.201800623

Cold season processes contribute substantially to annual carbon (C) and nitrogen (N) budgets in boreal forest ecosystems, but little is known about how decomposition processes are affected at temperatures prevalent during wintertime. The aim of this study was to evaluate temperature responses of soil C and N processes and to test the hypothesis that there is a switch towards decomposing N‐rich material when soil temperatures drop to near 0°C. In the laboratory, soils from a boreal forest long‐term nutrient fertilization experiment were exposed to different temperatures varying from +2 to +15°C, and C mineralization, gross as well as net N mineralization/immobilization were estimated. Carbon mineralization declined exponentially as temperature decreased, whereas the response of N processes to temperature varied, with some indication that soil C and N processes are decoupled at low temperatures. We could only partially confirm that the decoupling between C and N processes at low temperature was due to a switch to N‐rich material, i.e., a change in the material undergoing decomposition. Overall, our results clearly showed that temperature responses of N processes cannot be inferred from C processes in boreal forest ecosystems, and that there is a need to improve our understanding of the relationship between the two across the range of temperatures experienced throughout the year. In particular, further research is required to establish and evaluate appropriate proxies for modelling the relationship of C and N processes at temperatures close to the freezing point.