A review of the importance of mineral nitrogen cycling in the plant-soil-microbe system of permafrost-affected soils—changing the paradigm

• Main Authors: Ramm, Elisabeth, Liu, Chunyan, Ambus, Per, Butterbach-Bahl, Klaus, Hu, Bin, Martikainen, Pertti J., Marushchak, Maija E., Mueller, Carsten W., Rennenberg, Heinz, Schloter, Michael, Siljanen, Henri M. P., Voigt, Carolina, Werner, Christian, Biasi, Christina, Dannenmann, Michael
• Format: Article in Journal/Newspaper
• Language: English
• Published: Institute of Physics Publishing Ltd 2022
• Subjects: ddc:550; Earth sciences; info:eu-repo/classification/ddc/550; Arctic; permafrost
• Online Access: https://publikationen.bibliothek.kit.edu/1000142245; https://publikationen.bibliothek.kit.edu/1000142245/142411918; https://doi.org/10.5445/IR/1000142245

The paradigm that permafrost-affected soils show restricted mineral nitrogen (N) cycling in favor of organic N compounds is based on the observation that net N mineralization rates in these cold climates are negligible. However, we find here that this perception is wrong. By synthesizing published data on N cycling in the plant-soil-microbe system of permafrost ecosystems we show that gross ammonification and nitrification rates in active layers were of similar magnitude and showed a similar dependence on soil organic carbon (C) and total N concentrations as observed in temperate and tropical systems. Moreover, high protein depolymerization rates and only marginal effects of C:N stoichiometry on gross N turnover provided little evidence for N limitation. Instead, the rather short period when soils are not frozen is the single main factor limiting N turnover. High gross rates of mineral N cycling are thus facilitated by released protection of organic matter in active layers with nitrification gaining particular importance in N-rich soils, such as organic soils without vegetation. Our finding that permafrost-affected soils show vigorous N cycling activity is confirmed by the rich functional microbial community which can be found both in active and permafrost layers. The high rates of N cycling and soil N availability are supported by biological N fixation, while atmospheric N deposition in the Arctic still is marginal except for fire-affected areas. In line with high soil mineral N production, recent plant physiological research indicates a higher importance of mineral plant N nutrition than previously thought. Our synthesis shows that mineral N production and turnover rates in active layers of permafrost-affected soils do not generally differ from those observed in temperate or tropical soils. We therefore suggest to adjust the permafrost N cycle paradigm, assigning a generally important role to mineral N cycling. This new paradigm suggests larger permafrost N climate feedbacks than assumed previously.