Flowering, seed production and seed mass in a species-rich temperate grassland exposed to FACE and warming

Long-term effects of climate change on plant communities must be mediated by reproductive and recruitment responses of component species. From spring 2003 until autumn 2006, we monitored flowering and seed-production responses to free air CO₂ enrichment (FACE) and 2°C warming in a species-rich, nutrient-poor southern temperate grassland, by using the TasFACE experiment. There were no effects of either FACE or warming on the proportion of species flowering in any year. Flowering, seed production and seed mass were not significantly affected by FACE, warming or their interaction in most species. Some species, however, did respond significantly to simulated global changes. These responses generally were not governed by life history, but there were two distinct trends. First, warming increased the proportion of the population that flowered in perennial grasses but not in other species types. Second, flowering and seed production of both perennial woody dicots responded strongly to the interaction of FACE and warming, with Bossiaea prostrata producing most seeds in warmed FACE plots and Hibbertia hirsuta producing the most in unwarmed FACE plots. FACE increased seed mass 4-fold in the perennial C₃ grass Elymus scaber (P < 0.01) but substantially reduced seed mass of the perennial C₃ grass Austrodanthonia caespitosa (P < 0.02) and the perennial forb Hypochaeris radicata (P < 0.02), with the remainder of species unaffected. Our results indicate that warming and elevated CO₂ had little effect on seed production in the temperate grassland ecosystem. The few significant affects there were, however, are likely to have substantial implications for community composition and structure.