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| Titel |
Seasonality in a boreal forest ecosystem affects the use of soil temperature and moisture as predictors of soil CO2 efflux |
| VerfasserIn |
S. M. Niinistö, S. Kellomäki, J. Silvola |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 8, no. 11 ; Nr. 8, no. 11 (2011-11-08), S.3169-3186 |
| Datensatznummer |
250006194
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| Publikation (Nr.) |
 copernicus.org/bg-8-3169-2011.pdf |
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| Zusammenfassung |
Our objectives were to identify factors related to temporal variation of
soil CO2 efflux in a boreal pine forest and to evaluate simple
predictive models of temporal variation of soil CO2 efflux. Soil
CO2 efflux was measured with a portable chamber in a Finnish Scots pine
forest for three years, with a fourth year for model evaluation. Plot
averages for soil CO2 efflux ranged from 0.04 to 0.90 g CO2 m−2 h−1
during the snow-free period, i.e. May–October, and from 0.04 to 0.13 g CO2 m−2 h−1 in winter. Soil temperature
was a good predictor of soil CO2 efflux. A quadratic model of
ln-transformed efflux explained 76–82 % of the variation over the
snow-free period.
The results revealed an effect of season: at a given temperature of the
organic layer, soil CO2 efflux was higher later in the snow-free period
(in August and September) than in spring and early summer (in May and June).
Regression coefficients for temperature (approximations of a Q10 value)
of month-specific models decreased with increasing average soil
temperatures. Efflux in July, the month of peak photosynthesis, showed no
clear response to temperature or moisture. Inclusion of a seasonality index,
degree days, improved the accuracy of temperature response models to predict
efflux for the fourth year of measurements, which was not used in building
of regression models. During peak efflux from mid-July to late-August,
efflux was underestimated with the models that included degree days as well
as with the models that did not. The strong influence of the flux of
photosynthates belowground and the importance of root respiration could
explain the relative temperature insensitivity observed in July and together
with seasonality of growth of root and root-associated mycorrhizal fungi
could explain partial failure of models to predict magnitude of efflux in
the peak season from mid-July to August.
The effect of moisture early in the season was confounded by simultaneous
advancement of the growing season and increase in temperature. In a dry
year, however, the effect of drought was evident as soil CO2 efflux was
some 30 % smaller in September than in the previous wet year. Soil
temperature was a good overall predictor of soil CO2 efflux, possibly
partly because its apparent effect was strengthened by many environmental
factors and ecosystem processes that varied in concert with its variation.
However, the consistent underestimation by the predictive models for the
peak season corroborates recent findings concerning the importance of
seasonal changes in carbon inputs to processes producing CO2 in soil. |
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