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| Titel |
Is optimality in stomatal conductance an endogenous process or an emergent property arising from interactions with the environment? |
| VerfasserIn |
Victor Resco De Dios, Arthur Gessler, Juan Pedro Ferrio, Michael Bahn, Alexandru Milcu, David Tissue, Jordi Voltas, Jacques Roy |
| 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 |
250131862
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| Publikation (Nr.) |
 EGU/EGU2016-12310.pdf |
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| Zusammenfassung |
| Plants are sessile and poikilothermic organisms that need to respond and adjust
promptly to an ever-changing environment. Over a single 24 h period, a plant may
experience the same level of variation in radiation as in its entire life-time and, in some
climates, the oscillation in day-night temperature and vapor pressure deficit might be of
similar magnitude to that experienced across a full year. Plants need to maintain
a positive C balance without depleting soil water reserves in the face of such a
diverse environment, and feedbacks between assimilation (A) and water losses (E)
are thought to have evolved to optimize stomatal conductance (gs). In short, the
optimal conductance hypothesis proposes that cross-talks between A and stomatal
conductance gs lead to a constant marginal water use (λ) during a day, such that A is
maximized and E minimized. The biological mechanism by which biochemical
processes would feedback gs remains unknown, but multiple studies have shown
empirical support for this hypothesis, leading to its current consideration of theory by
many.
Here we test whether optimal stomatal conductance is an endogenous property, that is,
driven solely by factors internal to the plant, and in the absence of environmental fluctuations.
After 5 days of entrainment, where monoculture canopies of bean and of cotton were
subjected to the average environmental conditions of an August sunny day in Montpellier (at
the CNRS European Ecotron, FR), we kept temperature, relative humidity and
photosynthetically active radiation constant for 48 h at the values observed at noon.
During this period, we monitored leaf gas exchange continuously every two minutes,
and canopy gas exchange every 15 minutes. We observed a periodic oscillation in
λ, showing a 24 h period, and consistent with a circadian regulation of water use
efficiency. Hourly variations in λ could thus not be explained by the optimal stomatal
hypothesis. Moreover, the pattern of variation (of maximal water use efficiency during the
“subjective” night hours, and minimal during the subjective daytime) indicate that
endogenous plant processes tend towards "wasting"’ water for maximizing A, instead of
optimizing water use. We thus conclude that optimal stomatal conductance, at least
in the species studied, is an emergent property resulting from interactions with
environmental cues. Models based on optimality theory are currently widespread within the
Earth System sciences, and our results shed new light into its mechanistic basis. |
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