Figure 6.

Effect of ambient UV-B radiation on potential PSII efficiency (F_v/F_m) during exposure of young sun leaves of mature A. excelsum trees to direct sunlight. A typical experiment is shown. In three independent further measurements, similar results were obtained upon 45 to 55 min of sun exposure and PAR doses between 4.2 and 5.5 mol m⁻²; due to varying irradiance caused by clouds, averaging of data was not possible. Upper panel, PAR under Aclar (+UV-B; ●) and Mylar (−UV-B; ○) films, respectively; lower panel, F_v/F_m as function of exposure time.