Growth, phenology and reproduction of an arid-environment winter ephemeral Dimorphotheca pluvialis in response to combined increases in CO2 and UV-B radiation

The winter ephemeral Dimorphotheca pluvialis was grown in open-top chambers in ambient or elevated CO2 (350 or 650 μmol mol−1), combined with ambient (2.39 to 7.59 kJ m−2 d−1) or increased (4.94 to 11.13 kJ m−2 d−1) UV-B radiation. Net CO2 assimilation rate and leaf water use efficiency increased in elevated CO2, but increased UV-B did not affect gas exchange. Leaf biomass was greater under increased UV-B, but vegetative biomass was unaffected in elevated CO2. Initiation of reproduction was delayed, and proportional investment in reproductive biomass at harvest was reduced in elevated CO2. Increased UV-B stimulated reproduction, particularly in ambient CO2, but also in elevated CO2 at a later stage. Changes in reproductive phenology and prolonged development in elevated CO2 during the stressful late season could indirectly be detrimental to reproductive success of D. pluvialis, but stimulation of reproduction by enhanced UV-B may to some extent mitigate this.