To test the hypothesis that UV filtering would de-harden plants and increase vulnerability to UV damage at PSII, desiccated plants from all three field treatments were subjected to a laboratory UV treatment, and Fv/Fm and ΦPSII were measured during simulated winter recovery conditions. There were no significant differences in Fv/Fm within each treatment group (UV-filtered, UV-transmitted, and site reference) at T0.5 and T192 after the laboratory UV treatment (Fig. S2A). At T24, UV-transmitted field plants that received a laboratory UV treatment had significantly higher Fv/Fm than UV-transmitted that did not. Similarly, ΦPSII of each treatment group was not significantly different after the laboratory UV treatment at T0.5 and T192, but at T24 was significantly higher in laboratory UV-treated UV-transmitted samples than UV-transmitted with no laboratory UV treatment (Fig. S2B).