Application of chlorophyll fluorescence to evaluate Mn tolerance of deciduous broad-leaved tree seedlings native to northern Japan

We used chlorophyll fluorescence to examine photosynthetic responses to excess Mn accumulation in leaves of four tree species differing in successional traits. Betula ermanii Cham. (Be) and Alnus hirsuta Turcz. (Ah) were studied as representatives of early-successional species. Ulmus davidiana Planch. var. japonica (Rehder) Nakai (Ud) was selected as a mid-successional species, and Acer mono Maxim. var. glabrum (Lév. et Van't.) Hara (Am) was chosen as a late-successional species. In Be, Ah and Am, high foliar concentrations of Mn had little effect on maximum photochemical efficiency of photosystem II (PSII), as indicated by the values of dark-adapted F(v)/F(m), whereas a significant decrease was observed in Ud. Photochemical quenching (qP) and the excitation capture efficiency of open PSII (F'(v)/F'(m)) decreased with increasing leaf Mn concentration at photosynthetic steady state after a 15-min exposure to 430 &mgr;mol m(-2) s(-1) PPFD. Compared with early-successional species, these decreases were greater in mid- and late-successional species leading to lower effective quantum efficiencies of PSII (DeltaF/F'(m) = qP x F'(v)/F'(m) = (F'(m) - F)/F'(m)). To determine the extent of photoinhibition, F(v)/F(m) of the illuminated leaves was remeasured after a 15-min dark period. Compared with the dark-adapted F(v)/F(m), we observed a significant decrease in F(v)/F(m) in Am leaves containing high concentrations of Mn. These chlorophyll fluorescence studies indicate that the early-successional species Be and Ah have a higher tolerance to excessive accumulations of Mn in leaves than the mid- and late-successional species Ud and Am.