Chlorophyll fluorescence of field-manipulated samples
F v/F m and ΦPSII were measured at three time points over a simulated winter recovery period (192 hours) to assess photosynthetic efficiency. At T0, desiccated samples from all three field treatment groups had very lowF v/F m values (mean UV-filtered = 0.044, mean UV-transmitted = 0.049, and mean site reference = 0.108). There was no statistical difference inF v/F m between any groups at T0 (Figure 2). After 24 hours in simulated winter recovery conditions, F v/F mhad increased in all samples. At T24,F v/F m of samples from UV-transmitting windows were significantly higher than those from UV-filtering windows (mean UV-filtered = 0.532, mean UV-transmitted = 0.599). Site reference samples had significantly higherF v/F m values (mean = 0.631) than UV-transmitted samples. At T192,F v/F m values of all treatments were also significantly different from each other in the same rank order: UV-transmitted were higher than UV-filtered, and site reference samples were higher than UV-transmitted; (mean UV-filtered = 0.790, mean UV-transmitted = 0.812, and mean site reference = 0.839). All treatment groups had relatively constant F o(relative to F m) over the simulated winter recovery period while F m increased from near 100 to at least 700 bits (Figure S4).
The pattern of ΦPSII measured at 150 µmol photons m-2s-1 over the recovery period was similar to that ofF v/F m. There was no statistical difference in ΦPSII between UV-filtered samples and UV-transmitted samples at T0 nor between ΦPSII values of site reference plants and UV-transmitted plants (Table 2). After 24 hours in recovery, ΦPSII of all samples had increased. ΦPSII of samples from UV-transmitting windows were significantly higher than those from UV-filtering windows. Site reference mean ΦPSII was 0.425, and there was no significant difference between site reference and UV-transmitted samples. At T192, neither UV-filtering and UV-transmitting, nor UV-transmitting and site reference ΦPSII values were significantly different from one another (site reference mean = 0.630).