A Comparison of Photosynthetic Responses to Water Stress in Seedlings From 3 Oak Species/ Quercus petraea (Matt) Liebl, Quercus rubra L and Qercus cerris L : Genetics of Oaks. IUFRO Proceedings

1993

S. 48-60

32 Lit. Ang.

Unselbständiges Werk

200041526

Photosynthetic responses of oak seedlings (Quercus petraea, Quercus rubra and Quercus cerris) to drought were investigated using gas-exchange and chlorophyll fluorescence. Decreases in predawn leaf water potential (Psi wp) led to pronounced reductions in both stomatal conductance and net CO2 assimilation rate (A). In contrast, the maximal photochemical efficiency of photosystem II (PS II) measured predawn remained unaffected until complete cessation of CO2 assimilation. Responses of PS II photochemical efficiency to increasing photon flux density (PFD) were determined for leaves of both control and water-stressed seedling. Drought resulted in a stronger reduction of at a given PFD in Quercus rubra and Quercus petraea, but not in Quercus cerris, and led to an overreduction of the primary electron acceptor pool (decrease in photochemical quenching. Such behavior could explain the observed increase in sensitivity to photoinhibition when these 2 species were water-stressed. In contrast, drought did not promote such an increase in the susceptibility of Quercus cerris leaves to photoinhibition.