Growth, phenology and reproduction of an arid-environment winter ephemeral Dimorphotheca pluvialis in response to combined increases in CO 2 and UV-B radiation

Abstract

The winter ephemeral Dimorphotheca pluvialis was grown in open-top chambers in ambient or elevated CO 2 (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 CO 2 assimilation rate and leaf water use efficiency increased in elevated CO 2, but increased UV-B did not affect gas exchange. Leaf biomass was greater under increased UV-B, but vegetative biomass was unaffected in elevated CO 2. Initiation of reproduction was delayed, and proportional investment in reproductive biomass at harvest was reduced in elevated CO 2. Increased UV-B stimulated reproduction, particularly in ambient CO 2, but also in elevated CO 2 at a later stage. Changes in reproductive phenology and prolonged development in elevated CO 2 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.