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| Titel |
Drought influence on carbon and water cycling in a Mediterranean Quercus suber L. woodland during the drought year 2012 |
| VerfasserIn |
Arndt Piayda, Maren Dubbert, Corinna Rebmann, Olaf Kolle, Filipe Costa e Silva, Alexandra Correia, Joao Santos Pereira, Christiane Werner, Matthias Cuntz |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250089238
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| Publikation (Nr.) |
 EGU/EGU2014-3434.pdf |
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| Zusammenfassung |
| Savannah-type ecosystems account for 26-30% of the global gross primary production with
water being one of the major driving factors. In Europe, savannah-type woodlands cover
an area of about 2-2.5 million ha on the Iberian Peninsula. The recent past has
shown there a significant decrease of precipitation in winter and spring as well as a
decrease of total annual precipitation. Hence, strong effects on local water balance and
carbon sink strength have been reported due to these changes in the precipitation
regime.
The objective of this study is to quantify changes in the water balance, gross primary
productivity and carbon sink strength of a typical Portuguese savannah-type woodland
(montado) under the changed precipitation pattern of the drought year 2012 compared to the
wet year 2011. The physiological response of the dominant tree species Quercus suber
(L.) is evaluated, employing combined photosynthesis and stomatal conductance
modelling.
Precipitation effectiveness ratio increased up to 122% in the dry year 2012 due to ground
water access of the Q. suber trees leaving no water for ground water replenishment. By the
lack of water in the upper soil and deep ground water reservoirs, the understorey and
overstorey gross primary productions were reduced by 53% and 28% in 2012 compared to
2011, respectively, due to the late onset of the autumn rains in 2011 and an additional severe
winter/spring drought. However, on an annual basis, the ecosystem was a carbon sink in both
years, with a 61% reduced sink strength in the dry year 2012 compared to the wet
2011.
Applying a combined photosynthesis and stomatal conductance model, best model fit to
gross primary productivity and transpiration of Q. suber trees could be achieved keeping
apparent maximum carboxylation rate V c,max as well as stomatal conductivity parameter m
and vapor pressure deficit sensitivity parameter D0 of the stomatal conductance formulation
variable. The Q. suber trees showed 20% reduced stomatal conductance gs during the
drought period 2012 compared to 2011 expressed as a reduction in stomatal conductance
model parameter m. Hence, vapor pressure deficit sensitivity parameter D0 increased
under drought conditions in order to preserve the sensitivity of gs to vapor pressure
deficit vpd. In response to reduced leaf internal CO2 availability and increased leaf
temperatures, the trees strongly reduced apparent maximum carboxylation rate V c,max by
39% in 2012 compared to 2011. However, stomatal response was strongest at the
drought beginning while strongest reduction of V c,max occurred at the end of the
drought.
Our results suggest that, if the trend of decreasing annual precipitation and changed
precipitation pattern on the Iberian Peninsula continues, sustained effects on local
ground water reservoirs, understorey species composition and tree productivity
may be expected in the long-term. To successfully model the effect of drought on
the montado ecosystem, variable apparent maximum carboxylation rate V c,max,
stomatal conductivity parameter m and vapor pressure deficit sensitivity parameter D0
need to be incorporated in photosynthesis and stomatal conductance modelling. |
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