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| Titel |
Seasonal change in CO2 and H2O exchange between grassland and atmosphere |
| VerfasserIn |
N. Saigusa, S. Liu, T. Oikawa, T. Watanabe |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 14, no. 3 ; Nr. 14, no. 3, S.342-350 |
| Datensatznummer |
250012215
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| Publikation (Nr.) |
 copernicus.org/angeo-14-342-1996.pdf |
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| Zusammenfassung |
| The seasonal change in CO2 flux
over an artificial grassland was analyzed from the ecological and meteorological
point of view. This grassland contains C3 and C4 plants;
the three dominant species belonging to the Gramineae; Festuca elatior (C3)
dominated in early spring, and Imperata cylindrica (C4) and Andropogon
virginicus (C4) grew during early summer and became dominant in
mid-summer. CO2 flux was measured by the gradient method, and the
routinely observed data for the surface-heat budget were used to analyze the CO2
and H2O exchange between the grassland and atmosphere. From August to
October in 1993, CO2 flux was reduced to around half under the same
solar-radiation conditions, while H2O flux decreased 20% during the
same period. The monthly values of water use efficiency, i.e., ratio of CO2
flux to H2O flux decreased from 5.8 to 3.3 mg CO2/g H2O
from August to October, the Bowen ratio increased from 0.20 to 0.30, and the
ratio of the bulk latent heat transfer coefficient CE to the
sensible heat transfer coefficient CH was maintained around
0.40-0.50. The increase in the Bowen ratio was explained by the decrease in air
temperature from 22.3 °C in August to 16.6 °C in October without considering
biological effects such as stomatal closure on the individual leaves. The nearly
constant CE/CH ratios suggested that the
contribution ratio of canopy resistance to aerodynamic resistance did not change
markedly, although the meteorological conditions changed seasonally. The
decrease in the water use efficiency, however, suggested that the photosynthetic
rate decreased for individual leaves from August to October under the same
radiation conditions. Diurnal variations of CO2 exchange were
simulated by the multi-layer canopy model taking into account the differences in
the stomatal conductance and photosynthetic pathway between C3 and C4
plants. The results suggested that C4 plants played a major role in
the CO2 exchange in August, the contribution of C4 plants
decreased in September, and daily variations of CO2 exchange were
mainly due to C3 plants in October. The results also suggested that
the decrease in the net canopy CO2 exchange from August to October
was induced partly by the decrease of net photosynthesis on the individual
leaves in both C4 and C3 plants, which could be due to
aging of the leaves. |
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