While the influence of elevated CO2 on the production, mass and quality of plant seeds has been well studied, the effect of warming on these characters is largely unknown; and there is practically no information on possible interactions between warming and elevated CO2, despite the importance of these characters in population maintenance and recovery. Here, we present the impacts of elevated CO2 and warming, both in isolation and combination, on seed production, mass, quality, germination success and subsequent seedling growth of Austrodanthonia caespitosa, a dominant temperate C3 grass from Australia, using seeds collected from the TasFACE experiment. Mean seed production and mass were not significantly affected by either elevated CO2 or warming, but elevated CO2 more than doubled the proportion of very light, inviable seeds (P < 0.05) and halved mean seed N concentration (P < 0.04) and N content (P < 0.03). The dependence of seed germination success on seed mass was affected by an elevated CO2× warming interaction (P < 0.004), such that maternal exposure to elevated CO2 or warming reduced germination if applied in isolation, but not when applied in combination. Maternal effects were retained when seedlings were grown in a common environment for 6 weeks, with seedlings descended from warmed plants 20% smaller (P < 0.008) with a higher root : shoot ratio (P < 0.001) than those from unwarmed plants. Given that both elevated CO2 and warming reduced seed mass, quality, germinability or seedling growth, it is likely that global change will reduce population growth or distribution of this dominant species.
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