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| Titel |
Physiological and morphological controls on the impact of high evaporative demand across different plant types |
| VerfasserIn |
Kadmiel Maseyk, Céline Lett, Markus Schmidt, Philippe Biron, Patricia Richard, Thierry Bariac, Ulli Seibt |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250052682
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| Zusammenfassung |
| Plant responses to climatic variability rely on both physiological and morphological
adaptations which operate at different scales for different means, and will therefore have
important consequences for responses to a change in the average climatic conditions.
With the increasing temperatures predicted across Europe and the Mediterranean in
the coming century, the incidence of heat waves and periods of high evaporative
demand are anticipated to become more frequent. As conditions during these events
can pass species’ tolerance thresholds, they can have a disproportionate impact on
species composition. We have investigated the response to a strong diurnal-scale
increase in atmospheric vapour pressure deficit (VPD) in four species representing
temperate broadleaf (Fagus sylvatica, Quercus robur), Mediterranean broadleaf (Q.
ilex) and Mediterranean conifer (Pinus nigra) growth types. Small (~1.5 m) potted
trees of all species were maintained under the same conditions outside, and during
the course of the experimental day VPD increased from 0.8 to 3.2 kPa (~40%
relative humidity) within 6 hours. Leaf-level responses to the sharp increase in
evaporative demand were investigated using a combination of gas exchange and isotopic
measurements.
All species experienced stomatal closure with increasing VPD, but there was a clear
difference in the response between the Mediterranean and temperate region species. In the
beech and English oak, stomatal conductance decreased to ~0.02 mol m-2 s-1
and was at near minimum values at a VPD of 1.5 – 2.0 kPa, whereas in the pine
and Holm oak, minimal stomatal conductance was ~0.05 mol m-2 s-1 and was
reached at a VPD of 2.5 kPa. Consequently transpiration rates were 2 – 3 times
greater in Q. ilex and P. nigra compared to the temperate broadleaves, and similar
between the two species (1 – 2 mmol m-2 s-1). While there was a clear separation
between the two groups of different origin in the physiological data, the leaf water
isotope data revealed a separation based on morphology. All species had similar
early morning leaf water isotopic composition (δ18Ol of 4 – 5 ), and all became
progressively enriched during the day. However, despite similar transpiration and
conductance values, end of the day enrichment was greater in Q. ilex (δ18Ol of 19 )
compared to P. nigra (12 ), but neither appeared to reach isotopic steady-state.
Leaf-water enrichment in the two other low transpiration broadleaf species was
similar to that in Q. ilex, and did appear to reach isotopic steady-state coinciding
with stability in gas exchange responses. These results show that while both the
southern latitude sclerophyllous Q. ilex and pine are less sensitive to conditions of high
evaporative demand, lower leaf-water turnover rates in the conifer species may also
potentially provide stronger buffering against persistent dry atmospheric conditions. |
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