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Umsatz der organischen Substanz in Waldböden unter erhöhtem N-Eintrag: In situ Tracerversuche mit 13C und 15N markierter Buchenstreu

English title Turnover of organic matter in forest soils under increased N deposition: Clues from tracer experiments with 13C and 15N labelled beech litter
Applicant Hagedorn Frank
Number 112021
Funding scheme Project funding (Div. I-III)
Research institution Swiss Federal Research Inst. WSL Direktion
Institution of higher education Swiss Federal Institute for Forest, Snow and Landscape Research - WSL
Main discipline Pedology
Start/End 01.01.2007 - 30.06.2010
Approved amount 201'094.00
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Keywords (15)

biogeochemistry; carbon sequestration; forest ecology; global change; N deposition; Dissolved organic carbon; Lignin degradation; Litter decomposition; Microbial biomass; Nitrogen deposition; PLFA; Soil organic matter; Soil respiration; Stable isotopes; Tracer

Lay Summary (English)

Lead
Lay summary
Aims
The objectives are to study how increased atmospheric N deposition will affect soil organic matter turnover. We will add large amounts of double-labelled (13C and 15N) beech litter, leafs and wood-chips, to forest soil and to trace the fate of the added C and N through the soil system under ambient and experimentally increased N inputs (+50 kg NH4NO3-N ha-1y-1).

Scientific Background
Soils contain the largest fraction of the terrestrial carbon pools. Their role as sinks for atmospheric CO2, however, is strongly debated. One of the unknowns is the impact of the currently increased N deposition to forest ecosystems. Nitrogen is the limiting nutrient for many processes in the plant and soil system, and as the cycling of C and N are tightly coupled, increased N deposition affects also the cycling of soil organic matter (SOM). Modelling studies suggest that increased N inputs stimulate the turnover of C due to decreasing C/N ratios. In contrast, many field studies have shown that higher N inputs suppress CO2 effluxes from soils.Recent radiocarbon studies and 13C tracer experiments have indicated that N deposition retards particularly the decomposition of older and stable SOM-pools and thus, increased N inputs might lead to a sequestration of C in the long-term. The underlying mechanisms of this preservation effect, however, are not well known.

Methods
We will add 13C and 15N-labelled litter (leafs and wood) from a previousCO2 enrichment experiment to soils and we will follow the fate of the added C and N in the litter itself, in mineral soils and their microbial communities, in leached DOC, and in respired CO2.

Expected Results
The tracing of litter-derived C and N in soils will allow us (1) to identify how increased N deposition affects CO2 effluxes and DOC leaching and (2) to estimate which SOM-pools (labile litter-derived or stabile SOM) respond most sensitive to the increased N inputs. (3) To test if high N inputs in fact retard lignin degradation as hypothesized by some authors, we intend to gain insight into underlying mechanisms by tracing the fate of the labelled lignin monomers in the litter itself, soils, and in DOC and by measuring the activity of lignin degrading enzymes. (4) To elucidate if N deposition changes the microbial communities, e.g. by favouring fast growing microbes specialised on fresh substrate and suppressing slow-growing microbes relying mainly on SOM, we will analyse the 13C in phospholipid fatty acids extracted from soils and from the decomposing litter. (5) To identify how the litter-derived N becomes stabilised in soils, we will trace the 15N signal into physically separated pools of SOM with turnover rates known from their 13C signature.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

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Associated projects

Number Title Start Funding scheme
126778 Nitrogen effect on molecular dynamics in forest soils 01.05.2010 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)

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