Exotic plant species are locally adapted but not to high ultraviolet‐B radiation: a reciprocal multispecies experiment

Abstract

Ultraviolet (UV) radiation intensities differ among global regions, with significantly higher levels in the southern hemisphere. UV‐B may act as an environmental filter during plant invasions, which might particularly apply to plant species from Europe introduced to New Zealand. Just like for any other abiotic or biotic filter, successful invaders can cope with novel environmental conditions via plastic responses and/or through rapid adaptation by natural selection in the exotic range. We conducted a multispecies experiment with herbaceous plants in two common gardens located in the species’ native and exotic ranges, in Germany and New Zealand, respectively. We used plants of German and New Zealand origin of eight species to test for adaptation to higher UV‐B radiation in their new range. In each common garden, all plants were exposed to three radiation treatments: (1) ambient sunlight, (2) exclusion of UV‐B while transmitting ambient UV‐A, and (3) combined exclusion of UV‐B and UV‐A. Linear mixed‐effect models revealed significant effects of UV‐B on growth and leaf traits and an indication for UV‐B‐induced biomass reduction in both common gardens pointing to an impact of natural, ambient UV radiation intensities experienced by plants in the northern and in the southern hemisphere. In both common gardens, the respective local plants (i.e., German origins in Germany, New Zealand origins in New Zealand) displayed enhanced productivity and aboveground biomass allocation, thus providing evidence for recent evolutionary processes in the exotic range. Genetic differentiation between different origins in consequence of divergent local selection pressures was found for specific leaf area. This differentiation particularly hints at different selective forces in both ranges while only little evidence was found for an immediate selective effect of high UV‐B intensities in the exotic range. However, reaction norm slopes across ranges revealed higher plasticity of exotic individuals in functional leaf traits that might allow for a more sensitive regulation of photoprotection measures in response to UV‐B. During the colonization, New Zealand populations might have been selected for the observed higher phenotypic plasticity and a consequently increased ability to successfully spread in the exotic range.

Combined Effects of UV-B and Drought on Native and Exotic Populations of Verbascum thapsus L.

“…In consequence, the applied UV-B intensity was familiar to the level exotic populations experience but novel to native individuals only. The observed limiting effects of UV-B radiation on leaf number, leaf length and rosette area confirm previous studies, which also reported UV-B-induced growth and biomass reduction [17,19,29,44]. A UV-B-induced increase in PSII efficiency was determined in the present study and caused by a decrease of minimum and maximum chlorophyll fluorescence (see also [45]).…”

“…Overall irradiation and biologically active UV-B radiation levels are equally subjected to climate change and are becoming more important for both resident plant communities and plant invasions [14]. However, these factors have been largely neglected in plant invasion research (see however: [15][16][17]). The effects of global change have largely been under consideration to date as 'one-factor-only' approaches.…”

Native distribution characteristics rather than functional traits explain preadaptation of invasive species to high‐UV‐B environments

“…The higher the mean UV‐B intensities in their native range, the higher was the LDMC ind under UV‐B radiation exposure. As LDMC is known for its ability to respond plastically and its protective effect against high‐energy radiation, one could expect a more pronounced response of preadapted species as observed in the experiment (Hock et al., 2019; Robson et al., 2015).…”

“…Higher leaf number of plants in the New Zealand experiment either indicates a generally more productive environment in comparison to the German common garden (see Hock et al., 2019) or a functional response to different environmental conditions that could not be controlled for in the experiments. Such differences might be a result of several biotic and abiotic factors, most notably those related to higher temperature or more sunshine hours, but might also derive from altered biotic interactions.…”

“…high UV B, drought), as it induces protective responses of the photosynthetic apparatus and therefore increases physiological resilience (Escobar‐Bravo, Klinkhamer, & Leiss, 2017; Štroch et al., 2015; Verdaguer, Jansen, Llorens, Morales, & Neugart, 2017). Furthermore, the differences in the level of UV radiation between native and exotic ranges allow disentangling the effect of UV radiation on plant growth and development in the context of the local environments (Hock et al., 2019).…”