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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-176
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-176
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 03 Jun 2019

Submitted as: research article | 03 Jun 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Preferential protein depolymerization as a preservation mechanism for vascular litter decomposing in Sphagnum peat

Hendrik Reuter1, Julia Gensel2, Marcus Elvert2, and Dominik Zak3 Hendrik Reuter et al.
  • 1Department of Chemical Analytics and Biogeochemistry, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, DE-12587 Berlin, Germany
  • 2MARUM - Center for Marine Environmental Sciences and Faculty of Geosciences, University of Bremen, DE-28359 Bremen, Germany
  • 3Department of Bioscience, University of Aarhus, DK-8600 Silkeborg, Denmark

Abstract. Nitrogen (N) dynamics in Phragmites australis litter due to anaerobic decomposition in three anoxic wetland substrates were analyzed by elemental analyses and infrared spectroscopy (FTIR). After 75 days of decomposition, a relative accumulation of bulk N was detected in most litters, but N accumulated less when decomposition took place in a more N-poor environment. FTIR was used to quantify the relative content of proteins in litter tissue and revealed a highly linear relationship between bulk N content and protein content. Changes in bulk N content thus paralleled and probably were governed by changes in litter protein content. Such changes are the result of two competing processes within decomposing litter: enzymatic protein depolymerization as a part of the litter breakdown process and microbial protein synthesis as a part of microbial biomass growth within the litter. Assuming microbial homeostasis, DNA signals in FTIR spectra were used to calculate the amount of microbial N in decomposed litter which ranged from 14 to 42 % of the total litter N for all leaf samples. Microbial carbon (C) content and resultant calculated carbon-use efficiencies (CUEs) indicate that microbial N in litter accumulated according to predictions of the stoichiometric decomposition theory. Subtracting microbial C- and N-contributions from litter, however, revealed decomposition site dependent variations in the percentual amount of remaining, still unprocessed plant N compared to remaining plant C, an indicator for preferential protein depolymerization. For all leaf litters, the coefficient of preferential protein depolymerization (α), which relates N-compound depolymerization to C-compound depolymerization, ranged from 0.74–0.88 in a nutrient-rich detritus mud to 1.38–1.82 in Sphagnum peat, the most nutrient-poor substrate in this experiment. Preferential protein depolymerization leads to a gradual N depletion of decomposing litter which we propose as a preservation mechanism for vascular litter decomposing in Sphagnum peat.

Hendrik Reuter et al.
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Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Hendrik Reuter et al.
Data sets

FTIR, CuO lignin, and bulk decomposition data of a 75-day anoxic Phragmites australis litter decomposition experiment in soil substrates from three northeast German wetlands H. Reuter, J. Gensel, M. Elvert, and D. Zak https://doi.pangaea.de/10.1594/PANGAEA.902181

Hendrik Reuter et al.
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Short summary
Using infrared spectroscopy, we developed a routine to disentangle microbial nitrogen (N) and plant N in decomposed litter. In a decomposition experiment in three wetland soils, this routine revealed preferential protein depolymerization as a decomposition site dependent parameter, unaffected by variations in initial litter N content. Especially in Sphagnum peat, preferential protein depolymerization led to an N-depletion of still unprocessed litter tissue, i.e. a gradual loss of litter quality.
Using infrared spectroscopy, we developed a routine to disentangle microbial nitrogen (N) and...
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