Effect of high light intensity on the photosynthetic apparatus of two hybrid lines of Paulownia grown on soils with different salinity

The objective of this investigation was to evaluate the simultaneous action of light stress and salinity. Pulse amplitude modulated chlorophyll fluorescence, P-700 redox state, and pigment analysis were used to assess the impact of high light intensity on Paulownia tomentosa x fortunei and Paulownia elongata x elongata grown on soils with different salinity. It was found that light stress reduced the amount of pigments and the efficiency of photochemical energy conversion, inhibited the maximum and the effective quantum yields of PSII photochemistry, decreased photochemical quenching and photosynthetic rate. Data also showed influence on the primary quinone acceptor (Q(A)) reoxidation, which led to the restriction of the electron flow from Q(A) to plastoquinone and stimulation of the cyclic electron flow. The possible reasons for the increased effects of the light stress under conditions of high salt concentration in soil for Paulownia tomentosa x fortunei are discussed.