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| Titel |
Spatial and temporal variability of carbon fluxes in African ecosystems - a CarboAfrica synthesis study |
| VerfasserIn |
Werner Leo Kutsch, Lutz Merbold, Bob Scholes |
| 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 |
250037985
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| Zusammenfassung |
| This study reports carbon and water fluxes between the land surface and atmosphere in eleven
different ecosystems in Sub-Saharan Africa, as measured using eddy covariance (EC)
technology. The ecosystems for which data were available ranged in mean annual rainfall
from 320mm (Sudan) to 1150mm (Republic of Congo) and include a spectrum of land cover
types (savannas, woodlands, croplands and grasslands). Data were analysed across the
network, in order to understand the driving factors for ecosystem respiration and carbon
assimilation, and to reveal the different water use strategies in these highly seasonal
environments. In addition to the spatial pattern, the temporal pattern that connects carbon
fluxes with water relations in savanna ecosystems were studied in detail in a savanna
ecosystem at Kruger National Park, South Africa and a miombo woodland in Western
Zambia.
Temporal variability: The regulation of canopy conductance was temporally
changing in two ways: changes due to phenology during the course of the growing
season and short-term (hours to days) acclimation to soil water conditions. The
most constant parameter was water use efficiency. It was influenced by humidity
(VPD) during the day, but the VPD response curve of water usage only changed
slightly during the course of the growing season, and decreased by about 30% during
the transition from wet to dry season. The regulation of canopy conductance and
photosynthetic capacity were closely related. This observation meets recent leaf-level
findings that stomatal closure triggers down-regulation of photosynthesis during
drought. Our results may show the effects of these processes on the ecosystem
scale.
Spatial variability: The same pattern was found at large spatial scales. Maximum carbon
assimilation rates were highly correlated with mean annual rainfall (r2=0.74) and were also
positively correlated with satellite-derived fAPAR. Ecosystem respiration was dependent on
temperature at all sites, and was additionally dependent on soil water content at sites
receiving less than 1000 mm of rain per year. All the ecosystems studied that were dominated
by C3-plants showed a strong decrease in the 30-minute assimilation rates at low
humidity (VPD > 2.0 kPa), while ecosystems dominated by C4-plants did not. |
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