EGU22-9792
https://doi.org/10.5194/egusphere-egu22-9792
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Alder-induced stimulation of soil gross nitrogen turnover in permafrost-affected peatlands of Northeast China

Elisabeth Ramm1, Chunyan Liu2, Carsten W. Mueller3, Silvia Gschwendtner4, Hongyu Yue2, Xianwei Wang5, Juliane Bachmann1, Joost A. Bohnhoff1, Ulrike Ostler1, Michael Schloter4,6, Heinz Rennenberg7, and Michael Dannenmann1
Elisabeth Ramm et al.
  • 1Institute of Meteorology and Climate Research, Atmospheric Environmental Research (IMK-IFU), Karlsruhe Institute of Technology (KIT), Garmisch-Partenkirchen 82467, Germany (elisabeth.ramm@kit.edu)
  • 2State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, P. R. China
  • 3Department of Geosciences and Natural Resource Management, University of Copenhagen, Copenhagen DK-1350, Denmark
  • 4Research Unit for Comparative Microbiome Analyses Helmholtz Zentrum München, Oberschleissheim 85764, Germany
  • 5Key Laboratory of Wetland Ecology and Environment, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130102, P. R. China
  • 6Chair of Soil Science, Science Center Weihenstephan, Department of Ecology and Ecosystem Management, Technical University Munich, Freising 85354, Germany
  • 7Center of Molecular Ecophysiology (CMEP), College of Resources and Environment, Southwest University, Chongqing 400715, P. R. China

Unlike carbon dynamics, nitrogen (N) dynamics in permafrost peatlands are not well-studied. For the prediction of permafrost N climate feedbacks, a better process-based understanding of the N cycle in permafrost peatlands is however urgently needed. Therefore, we characterized and quantified soil organic matter, soil gross microbial N turnover and soil-atmosphere exchange of nitrous oxide (N2O) on the southern edge of the Eurasian permafrost area in situ (www.nifroclim.de). Specifically, we sampled a tree-free lowland peatland and a lowland peatland with an N2-fixing alder forest in Northeast China.

Nuclear magnetic resonance spectroscopy revealed more recalcitrant organic matter at greater depth and more bioavailable organic matter substrates in upper peat horizons. In line with this result, gross ammonification and nitrification generally decreased with increasing sampling depth. Gross rates of mineral N turnover in the active layers of the tree-free peatland were comparable to those of temperate ecosystems. Despite substantial gross ammonification, the low nitrification:ammonification ratios and negligible soil N2O emissions still depicted a closed N cycle characterized by N limitation in the tree-free peatland.

In strong contrast, the peatland underneath the alder forest showed an accelerated N turnover with very high gross rates of ammonification (3.1 g N m-2 d-1) and nitrification (0.6 g N m-2 d-1), exceeding those of the alder-free peatland by an order of magnitude. This was accompanied by substantial N2O emissions. The increase in gross N turnover was most pronounced in the rooted soil layer, where N inputs from biological N fixation almost doubled total N concentrations and halved the ratios of soil organic carbon to total N. The frozen ground underneath alder trees contained strongly increased ammonium concentrations prone to be released upon thaw. This study shows that alder forests that further expand on permafrost-affected peatlands with global change create hot spots of soil mineral N turnover, thereby potentially enhancing permafrost N climate feedbacks.

How to cite: Ramm, E., Liu, C., Mueller, C. W., Gschwendtner, S., Yue, H., Wang, X., Bachmann, J., Bohnhoff, J. A., Ostler, U., Schloter, M., Rennenberg, H., and Dannenmann, M.: Alder-induced stimulation of soil gross nitrogen turnover in permafrost-affected peatlands of Northeast China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9792, https://doi.org/10.5194/egusphere-egu22-9792, 2022.

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