1. Photosynthesis of oak trees [Quercus petraea (Matt.) Liebl.] during drought under field conditions: diurnal course of net CO2 assimilation and photochemical efficiency of photosystem II.
- Author
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Epron, D., Dreyerr, E., and Bréda, N.
- Subjects
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CARBON dioxide , *DROUGHTS , *DURMAST oak , *OAK , *PHOTOSYNTHESIS , *EFFECT of atmospheric carbon dioxide on plants , *CHLOROPHYLL - Abstract
Adult trees of Quercus petraea were submitted to controlled water shortage in a natural stand near Nancy, France. Diurnal course of net CO2 assimilation rate (A) was measured in situ together with chlorophyll a fluorescence determined on dark adapted leaves. In 1990, trees experienced a strong water stress, with predawn and midday leaf water potentials below -2.0 and -3.0Mpa, respectively, Diurnal course of A of well-watered trees exhibited sometimes important midday decreased in A related to high temperature and vapour pressure deficit. Decreased in initial (Fo) and maximal (Fm) fluorescence and sometimes in photochemical efficiency of photosystem II (Fv/Fm) were observed and probably revealed the onset of mechanisms for thermal de-excitation. These mechanisms were shown to be sensitive to dithiothreitol. All these effects were reversible and vanished almost completely overnight. Therefore, they may be considered as protective mechanisms adjusting activity of photo-system II to the electron requirement for photosynthesis. Water stress amplified these reactions: A was strongly decreased, showing important midday depression; diurnal reductions in Fm and (Fv/Fm) were enhanced. The same trends were observed during summer 1991, despite a less marked drought, These protective mechanisms seemed very effective, as no photoinhibitory damage to PS II could be detected in either water stressed or control trees. [ABSTRACT FROM AUTHOR]
- Published
- 1992
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