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| Titel |
Subalpine grassland carbon dioxide fluxes indicate substantial carbon losses under increased nitrogen deposition, but not at elevated ozone concentration |
| VerfasserIn |
Matthias Volk, Daniel Obrist, Kris Novak, Robin Giger, Seraina Bassin, Jürg Fuhrer |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250035556
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| Zusammenfassung |
| Ozone (O3) and nitrogen (N) deposition affect plant carbon (C) dynamics and may
thus change ecosystem C-sink/-source properties. We studied effects of increased
background O3 concentrations (up to ambient x 2) and increased N deposition (up to
+50 kg ha-1 a-1) on mature, subalpine grassland during the third treatment year.
During ten days and 13 nights, covering the vegetation period of 2006, we measured
ecosystem-level CO2 exchange using a steady state cuvette. Light dependency of gross
primary production (GPP) and temperature dependency of ecosystem respiration rates
(Reco) were established. Soil temperature, soil water content, and solar radiation
were monitored. Using Reco and GPP values, we calculated seasonal net ecosystem
production (NEP), based on hourly averages of global radiation and soil temperature.
Differences in NEP were compared to differences in soil organic C after five years of
treatment.
Under high O3 and with unchanged aboveground biomass, both mean Reco and GPP
decreased throughout the season. Thus, NEP indicated an unaltered growing season CO2-C
balance. Under high N treatment, with a +31% increase in aboveground productivity, mean
Reco, but not GPP increased. Consequently, seasonal NEP yielded a 53.9 g C m-2 (± 22.05)
C loss compared to control. Independent of treatment, we observed a negative NEP of 146.4 g
C m-2 (±15.3). This C loss was likely due to a transient management effect, equivalent to a
shift from pasture to hay meadow and a drought effect, specific to the 2006 summer climate.
We argue that this resulted from strongly intensified soil microbial respiration,
following mitigation of nutrient limitation. There was no interaction between O3 and N
treatments.
Thus, during the 2006 growing season, the subalpine grassland lost >2% of total topsoil
organic C as respired CO2, with increased N deposition responsible for one-third of that loss. |
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