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| Titel |
Current photosynthate fuels the nitrogen response of soil CO2 flux in a boreal forest |
| VerfasserIn |
John Marshall, Matthias Peichl, Lasse Tarvainen, Torgny Näsholm, Mats Öquist, Sune Linder |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250142629
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| Publikation (Nr.) |
 EGU/EGU2017-6270.pdf |
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| Zusammenfassung |
| Nitrogen addition frequently reduces CO2 efflux from forest soils, but it has been unclear
whether the effect is on fluxes of current photosynthate belowground or the oxidation of
substrate to CO2. Pulse-chase and girdling experiments have shown that current
photosynthate can be a major substrate for soil CO2 efflux, but these methods are unwieldy
for describing seasonal patterns. In the current study, we placed transparent chambers on the
soil surface beneath a forest canopy and measured the seasonal CO2 flux over three growing
seasons (2012-2014) in a boreal Scots pine forest under repeated, heavy nitrogen (N) addition
(50-100 kg N ha−1 yr−1). Net CO2 fluxes were measured every half hour using a unique
system comprised of four large (each 20.3 m2 surface area) chambers, two each on the
nitrogen treatment and the control. Base respiration rates (R0) and temperature
sensitivity (Q10) were derived from nonlinear fits to the flux data. The Q10 was
similar with or without N addition, but the nitrogen additions nearly halved the
R0 values. Treatment differences in R0 appeared in May or June, peaked in July and
August, and disappeared again in November. This pattern is consistent with the
seasonality of photosynthesis at our boreal site. We estimated efflux in the absence
of new photosynthate by extrapolating the May and November parameterization
throughout the year. These extrapolations agreed with independent estimates through the
winter snowpack and with the results of previous tracer and girdling experiments,
supporting the contention that new photosynthate accounts for the nitrogen-induced
reduction in CO2 efflux. Soil organic matter accumulated in the N addition treatment
at a rate that quantitatively matched the reduction in CO2 efflux. We therefore
conclude that the reduced CO2 efflux following N addition is due to a decrease in
the oxidation of new photosynthate, whereas its delivery belowground remains unaltered. |
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