Dark-leaved willow (Salix myrsinifolia) is resistant to three-factor (elevated CO2, temperature and UV-B-radiation) climate change.

Elevated carbon dioxide (CO2 ), temperature (T) and ultraviolet-B (UV-B) radiation may affect plant growth and secondary chemistry in different directions, but the effect of the combination of the three factors has seldom been tested. Here, we grew four dark-leaved willow (Salix myrsinifolia) clones under combinations of ambient or elevated CO2, T and UV-B radiation in top-closed chambers for 7 wk. Elevated UV-B had no effects on growth or phenolic compounds, and there were no significant interactions between UV-B, CO2 and T. CO2 alone increased most growth parameters, but the magnitude of the effect varied among the clones. Total phenolics increased at elevated CO2 , whereas they decreased at elevated T. The responses varied between the clones. The results imply that dark-leaved willow are fairly resistant to the applied three-factor climate change, probably because of high constitutive defense. However, the interactions between clone and climate change factors implies that some clones are more susceptible than the species as a whole.