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| Titel |
Constraining key hydraulic parameters of Scots Pine through sapflow data assimilation along a climatic gradient |
| VerfasserIn |
O. Sus, J. Martínez-Vilalta, R. Poyatos, M. Williams |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250067825
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| Zusammenfassung |
| In order to model the water balance of a forest ecosystem and predict its response to
environmental changes, the response of tree transpiration to environmental conditions needs
to be simulated. The plant hydraulic system can be conceptualised as a series of hydraulic
resistances. The flow of water between any two locations of this system is proportional to the
hydraulic conductivity and the water potential gradient linking them. The different
components of the plant hydraulic system can change during drought as a result of
varying stomatal conductance, xylem hydraulics and the regulation of leaf and root
area.
However, within this soil-plant-atmosphere continuum (SPAC), physical processes of
water flow are better understood than plant hydraulics. For example, the effects of
leaf microclimate on stomatal regulation of transpiration are not well understood.
Moreover, little is known about how key hydraulic traits vary seasonally or as a
function of environmental conditions. Within corresponding models, empirical
parameters are introduced as surrogates for a range of complex and/or unknown
mechanisms.
Data assimilation (DA) methodology has shown to be a useful technique for model
parameter estimation in various disciplines of the geosciences. However, few studies have
applied DA to constrain parameter values within the SPAC in forest transpiration
models. DA could prove to be particularly useful in quantifying these parameters,
which are often not directly measurable. Sapflow data are highly appropriate for this
purpose, as they are the measurable end-product of water transport through the
SPAC in response to environmental conditions. Accordingly, these data provide
temporally highly resolved, direct constraints on associated key parameters within
models.
In this study, we assimilated sapflow data from three different Scots Pine sites – following
a climatic gradient from the southern dry limit of its distribution (southern Catalunya, Spain)
up to the northern temperate zone (Scotland) – into a process-based ecosystem model (SPA).
Within SPA, photosynthesis and transpiration are linked by a stomatal conductance module
that maximises daily carbon gain per unit leaf nitrogen within the limitations of
canopy water storage and soil to canopy water transport. At each site, sap flow
was measured using the Granier method for a representative period, covering from
several months in the growing season up to a whole year. Applying a sequential DA
technique (EnKF), we constrained key hydraulic and structural parameters (root and
aboveground plant resistance to water transport, minimum leaf water potential, root to
leaf mass ratio) and further analysed apparent patterns of seasonal and latitudinal
variability. We conducted the assimilation experiments with both synthetic (i.e.
model generated) and real sapflow data in order to estimate the applicability of
the DA methodology. Our results are complementary to field site experiments by
providing independent insights into stand-scale plant hydraulics, which bear further
implications on water use efficiency and hydraulic limitations on carbon assimilation. |
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