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Nitrogen effect on molecular dynamics in forest soils

English title Nitrogen effect on molecular dynamics in forest soils
Applicant Schmidt Michael W. I.
Number 126778
Funding scheme Project funding (Div. I-III)
Research institution Geographisches Institut Universität Zürich
Institution of higher education University of Zurich - ZH
Main discipline Pedology
Start/End 01.05.2010 - 30.04.2013
Approved amount 194'913.00
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Keywords (11)

amino sugars; CO2 fumigation; compound-specific isotope analysis; forest soil; fungal biomarkers; gas chromatography; lignin; microbial biomarkers; nitrogen deposition; plant biomarkers; fungi

Lay Summary (English)

Lay summary
Human activity affects ecosystems in multiple ways. Beside the intensively discussed carbon dioxide (CO2) emissions from fossil fuel burning, there has also been a strong increase in the release of reactive nitrogen-containing compounds into the atmosphere during the last decades. These compounds are subsequently deposited in ecosystems. As nitrogen is the most important plant nutrient, this nitrogen deposition results in a fertilization of ecosystems via the atmosphere. It has been suggested that this fertilization leads to increased tree growth and thus removes CO2 from the atmosphere, which would be a positive effect. However, most of the carbon in a forest is not stored in the trees but in the soil. Nitrogen additions to soil can lead to increased decomposer activity in soil, resulting in higher CO2 production and thus to a loss of soil carbon. Sometimes, however, an opposite effect of nitrogen on soil carbon has been observed. The reasons for these variable nitrogen effects on soil carbon are not yet understood.In this project, we want to test the hypothesis that the nitrogen effect varies with soil organic matter quality. The carbon stored in the soil as soil organic matter derives mainly from plant litter and microbial residues. These are chemically different from each other. An important difference is the nitrogen content which is much higher in microorganisms than in plants. These nitrogen-rich organic matter fractions may react differently to nitrogen deposition than nitrogen-poor plant litter.In order to test this hypothesis, we will combine biomarker analysis with stable isotope tracing in soil from an experiment that combined CO2 addition and nitrogen deposition to model forest ecosystems. Biomarkers are molecules that are specific for a certain origin. Lignin, for example, is a cell wall component of all higher plants, but does not occur in microorganisms. On the other hand, amino sugars are part of the bacterial cell walls but do not occur in plants. Stable isotopes allow the detailed tracing of added carbon or nitrogen into soil organic matter fractions.The project will contribute to our knowledge about the interactions between the nitrogen and carbon cycles in ecosystems, particularly in forest soils. Such an improved understanding is necessary in order to accurately predict the consequences of human nitrogen and carbon emissions on ecosystems, and to suggest mitigation options if necessary.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants


Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Swiss Soil Science Society 07.02.2013 Reckenholz
Biannual Meeting of the German Soil Science Society (DBG) 05.09.2011 Berlin, Germany


Title Year
Exchange visit of the European Science Foundation (ESF-MOLTER 2011

Associated projects

Number Title Start Funding scheme
112021 Umsatz der organischen Substanz in Waldböden unter erhöhtem N-Eintrag: In situ Tracerversuche mit 13C und 15N markierter Buchenstreu 01.01.2007 Project funding (Div. I-III)
172744 DEEP C 01.10.2017 Project funding (Div. I-III)
146850 Nitrogen effect on molecular dynamics in forest soils (end of thesis) 01.05.2013 Project funding (Div. I-III)
146850 Nitrogen effect on molecular dynamics in forest soils (end of thesis) 01.05.2013 Project funding (Div. I-III)


Soils are important components of the global carbon cycle. Increasing atmospheric nitrogen deposition can affect carbon storage in soils both via effects on biomass production and on decomposition processes. It has been observed that the effect of added N on decomposition processes varies between fresh litter and stable soil organic matter (SOM) fractions. Increased N deposition apparently retards the decomposition of recalcitrant litter and stable SOM, but the reasons for this preservation effect are not understood.During the last decade, several analytical techniques have evolved that give a deeper insight into dynamics of soil organic matter at a molecular level. Biomarker molecules have proven to be useful tools to determine the vegetal or microbial origin of soil organic matter. Compound-specific stable isotope analysis (CSIA) of C (13C) can be used to trace individual molecules in soil. Thus, it is possible to determine stability and turnover rates of microbial and plant residues in soil.Whereas studies in agroecosystems can profit from the natural 13C variations between some crop types, such a natural 13C label does not occur in forests. This has until now prevented the application of CSIA to forest soils. However, fumigation experiments with 13C-labeled CO2 present a possibility to study SOM dynamics in forests by CSIA. In the proposed project, we make use of archived soil samples from such a fumigation experiment. The unique experimental design of this study made it possible to study interactions between CO2 fumigation and N deposition on model forest ecosystems growing on two contrasting soils. By applying new analytical techniques (compound-specific isotope analysis on plant and microbial biomarkers), which were not yet available at the time when the experiment was performed, we will create added value to the already existing dataset from this experiment. This study can in many ways advance our knowledge on the molecular dynamics of soil organic matter:(1) It will provide the first systematic data on molecular dynamics in forest soils based on a 13C labeling approach.(2) It will provide the first systematic data on interactions between CO2, N and soil type on the dynamics of biomarkers in soil.(3) It will combine the use of different types of biomarkers of plant and microbial origin.(4) Localization of the labeled biomarkers in specific soil fractions will allow testing existing hypotheses on mechanisms of organic matter stabilization.In the frame of this study, we will also implement the analysis line for compound-specific isotope analysis in one of our laboratories, which will further strengthen our position in the front line of current research. To reach these goals, the study will profit from(1) the unique experimental design,(2) a large set of already published data available for this experiment, and (3) the synergies created from combining the experiences of the two working groups (biomarker and compound-specific isotope analysis at the University of Zurich, element cycling in forest ecosystems, at the Soil Biogeochemistry group at WSL).The proposed project has the potential to produce highly relevant results on the reaction of forest soils to changing environmental conditions (increase in atmospheric CO2 concentrations and in N deposition). Such data are urgently needed, as the IPCC report 2007 assesses soil nitrogen availability as a key factor in predicting future carbon sequestration by terrestrial ecosystems.