Photosynthesis of oak leaves under water stress: maintenance of high photochemical efficiency of photosystem II and occurrence of non-uniform CO2 assimilation
- 1 September 1993
- journal article
- research article
- Published by Oxford University Press (OUP) in Tree Physiology
- Vol. 13 (2) , 107-117
- https://doi.org/10.1093/treephys/13.2.107
Abstract
Net CO2 assimilation rates (A), stomatal conductance to water vapor (gw), photosynthetic O2 evolution in 5% CO2 (Amax) and photochemical efficiency of photosystem II were monitored in leaves of young oak saplings (Quercus petraea Matt. Liebl.) in response to increasing drought. Both A and gw declined rapidly as soon as predawn leaf water potential dropped below –1.0 MPa. The calculated intercellular concentration of CO2 first declined and then increased again as drought intensity increased, suggesting that both stomatal closure and a decreased ability of mesophyll chloroplasts to fix available CO2 were involved in the drought-induced reductions in A and gw. However, this assumption was not supported by the observations that, with increasing drought, the decline in Amax was limited, and the photochemistry of photosystem II and the quantum yield of light-driven electron transport remained stable. Autoradiograms of 14CO2-fed leaves revealed non-uniform assimilation rates during water stress. The consequences of a potential artifact induced by this patchiness on the calculation of intercellular CO2 concentration are discussed.Keywords
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