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| Titel |
Drought impact on carbon and water cycling in a Mediterranean Quercus suber L. woodland during the extreme drought event in 2012 |
| VerfasserIn |
A. Piayda, M. Dubbert, C. Rebmann, O. Kolle, F. Costa e Silva, A. Correia, J. S. Pereira, C. Werner, M. Cuntz |
| 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 ; 11, no. 24 ; Nr. 11, no. 24 (2014-12-16), S.7159-7178 |
| Datensatznummer |
250117741
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| Publikation (Nr.) |
 copernicus.org/bg-11-7159-2014.pdf |
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| Zusammenfassung |
Savannah-type
ecosystems account for 26–30% of global gross primary productivity GPP,
with water being one of the major driving factors. In Europe, savannah-type
woodlands cover an area of about 1.5 million ha. Here, the recent past has
shown a significant decrease in precipitation P in winter and spring as
well as a decrease in total annual precipitation. Strong effects on local
water balance and carbon sink strength have thus been reported due to changes
in precipitation regime.
The objective of this study is to quantify the impact of the extreme drought
event in 2012 on the water balance, gross primary productivity and carbon
sink strength of a typical Portuguese cork-oak woodland (montado)
compared to the wet year of 2011. Physiological responses of the dominant
tree species Quercus suber (L.) are disentangled employing combined
photosynthesis and stomatal conductance modelling.
Precipitation effectiveness ET/P increased from 86% in 2011 to
122% in the 2012 dry year due to deep soil or groundwater access of the
Q. suber trees leaving no water for groundwater replenishment.
Understorey and overstorey GPP were strongly reduced, by 53 and 28%,
respectively, in 2012 compared to 2011, due to the late onset of the autumn
rains in 2011 and an additional severe winter/spring drought. However, the
ecosystem was still a carbon sink in both years, but with a 38% reduced
sink strength under extreme drought in 2012 compared to 2011. The combined
photosynthesis–stomatal conductance model yielded the best results if it was
allowed to adjust photosynthetic and stomatal parameters simultaneously. If
stomatal response was modelled with the Leuning approach, which allows for
a different sensitivity to vapour pressure deficit, the stomatal model
parameters were highly coupled. A change in either of the parameters needed
to be compensated by the other to guarantee a stable sensitivity of stomatal
conductance to assimilation, independent of variations in vapour pressure
deficit. The Q. suber trees showed a 37% reduced stomatal
conductance during the drought period of 2012 compared to 2011, due to water
supply limitations. In response to reduced leaf-internal CO2
availability, the trees strongly reduced the apparent maximum carboxylation
rate by 43% in 2012 compared to 2011. Unexpectedly, the optimum
temperature Topt of the maximum electron transport rate decreased
during the drought period, enhancing the susceptibility of the trees to high
temperature stress during the summer.
Our results suggest that, if the trend of decreasing annual precipitation and
changed precipitation patterns on the Iberian Peninsula continues, sustained
effects on local groundwater reservoirs, understorey species composition and
tree mortality have to be expected in the long term. To model the effect of
drought on the montado ecosystem successfully, variable apparent
maximum carboxylation rate Vc,max, stomatal conductance parameter
m and vapour pressure deficit
sensitivity parameter D0 need to be incorporated into
photosynthesis–stomatal conductance modelling. |
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