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| Titel |
Variable coupling between sap-flow and transpiration in pine trees under
drought conditions |
| VerfasserIn |
Yakir Preisler, Fyodor Tatarinov, Shani Rohatyn, Eyal Rotenberg, José M. Grünzweig, Dan Yakir |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250122100
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| Publikation (Nr.) |
 EGU/EGU2016-1042.pdf |
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| Zusammenfassung |
| Changes in diurnal patterns in water transport and physiological activities in response to
changes in environmental conditions are important adjustments of trees to drought.
The rate of sap flow (SF) in trees is expected to be in agreement with the rate of
tree-scale transpiration (T) and provides a powerful measure of water transport in the
soil-plant-atmosphere system. The aim of this five-years study was to investigate the temporal
links between SF and T in Pinus halepensis exposed to extreme seasonal drought in the Yatir
forest in Israel. We continuously measured SF (20 trees), the daily variations in stem diameter
(ΔDBH, determined with high precision dendrometers; 8 trees), and ecosystem
evapotranspiration (ET; eddy covariance), which were complemented with short-term
campaigns of leaf-scale measurements of H2O and CO2 gas exchange, water potentials, and
hydraulic conductivity. During the rainy season, tree SF was well synchronized with
ecosystem ET, reaching maximum rates during midday in all trees. However, during the dry
season, the daily SF trends greatly varied among trees, allowing a classification of trees
into three classes: 1) Trees that remain with SF maximum at midday, 2) trees that
advanced their SF peak to early morning, and 3) trees that delayed their SF peak to
late afternoon hours. This classification remained valid for the entire study period
(2010-2015), and strongly correlated with tree height and DBH, and to a lower
degree with crown size and competition index. In the dry season, class 3 trees (large)
tended to delay the timing of SF maximum to the afternoon, and to advance their
maximum diurnal DBH to early morning, while class 2 trees (smaller) advanced their SF
maximum to early morning and had maximum daily DBH during midday and afternoon.
Leaf-scale transpiration (T), measurements showed a typical morning peak in all
trees, irrespective of classification, and a secondary peak in the afternoon in large
trees only. Water potential and hydraulic conductivity in larger trees recovered
faster from midday depression than in smaller ones. We concluded that the observed
changes in the patterns of water flow into and out of the trees reflected differences in
the utilization of external and internal ‘water storage’. Large trees appear to rely
on sufficient internal water storage that filled up in the morning (max DBH) and
supported transpiration both in the morning and the afternoon, while SF increased
throughout the day to compensate for the depletion in water storage (SF maximum in the
afternoon). In contrast, small trees with insufficient internal water storage must rely on
soil water availability and maximize SF in the morning to support concurrent tree
transpiration, achieving some internal storage only in the afternoon, when T declines
and maximum daily DBH is observed. The results indicated also that trees with
insufficient internal storage, as can be detected by the simultaneous SF and DBH
patterns, are likely to be more vulnerable to drought-related mortality since soil water
availability may not be sufficient to support transpiration and stomata opening. |
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