Test for Photosystem II protection from UV radiation
At the same time that stems from the field were measured as in the
previous section, 10-15 additional shoots per sample were selected from
field-collected samples as above and given a UV radiation treatment in
the laboratory. Samples were kept dry and placed under four T8 reptile
bulbs (ReptiSun 10.0 UVB, Zoo Med Laboratories Inc., San Luis Obispo,
CA, USA) in culture dishes covered by UV-transmitting acrylic in order
to filter out UV-C wavelengths, which in nature are absorbed by earth’s
atmosphere. Lamps were placed 2.5 cm from specimens for a UV-A/B flux
rate of 80 µmol m-2 s-1 and 160 µmol
m-2 s-1 PAR for 14 hours (rotated
once during treatment). After the UV treatment, shoots were prepared for
chlorophyll fluorescence identically as above. A fan was placed to
circulate under the lamp and temperature and RH were monitored with an
iButton data logger (Maxim Integrated, San Jose, CA, USA; 26 °C mean
temperature, 19% mean RH).
Fluorescence data were gathered and analyzed as above with the
Shapiro-Wilk test (Shapiro & Wilk 1965) for normality and pairwise
Wilcoxon signed-rank tests forF v/F m and ΦPSII (Wilcoxon
1945). Additionally, to test the effects of the laboratory UV treatment,
Wilcoxon signed-rank tests were performed onF v/F m and ΦPSII across
laboratory treatments (with or without additional laboratory UV) within
each treatment group at each time point of recovery (T0,
T24, and T192). Significance was
adjusted for multiple-testing with the Benjamini and Hochberg method
(Benjamini & Hochberg 1995).