Contents Summary243I.Introduction244II.Effects of elevated [CO2] on flowering time245III.Mechanisms for altered flowering time in response to elevated [CO2]250IV.Conclusion252Acknowledgements253References253 Summary Flowering is a critical milestone in the life cycle of plants, and changes in the timing of flowering may alter processes at the species, community and ecosystem levels. Therefore understanding flowering‐time responses to global change drivers, such as elevated atmospheric carbon dioxide concentrations, [CO2], is necessary to predict the impacts of global change on natural and agricultural ecosystems. Here we summarize the results of 60 studies reporting flowering‐time responses (defined as the time to first visible flower) of both crop and wild species at elevated [CO2]. These studies suggest that elevated [CO2] will influence flowering time in the future. In addition, interactions between elevated [CO2] and other global change factors may further complicate our ability to predict changes in flowering time. One approach to overcoming this problem is to elucidate the primary mechanisms that control flowering‐time responses to elevated [CO2]. Unfortunately, the mechanisms controlling these responses are not known. However, past work has indicated that carbon metabolism exerts partial control on flowering time, and therefore may be involved in elevated [CO2]‐induced changes in flowering time. This review also indicates the need for more studies addressing the effects of global change drivers on developmental processes in plants.

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Summary• Atmospheric CO 2 concentration ([CO 2 ]) is rising on a global scale and is known to affect flowering time. Elevated [CO 2 ] may be as influential as temperature in determining future changes in plant developmental timing, but little is known about the molecular mechanisms that control altered flowering times at elevated [CO 2 ].• Using Arabidopsis thaliana, the expression patterns were compared of floralinitiation genes between a genotype that was selected for high fitness at elevated [CO 2 ] and a nonselected control genotype. The selected genotype exhibits pronounced delays in flowering time when grown at elevated [CO 2 ], whereas the control genotype is unaffected by elevated [CO 2 ]. Thus, this comparison provides an evolutionarily relevant system for gaining insight into the responses of plants to future increases in [CO 2 ].• Evidence is provided that elevated [CO 2 ] influences the expression of floral-initiation genes. In addition, it is shown that delayed flowering at elevated [CO 2 ] is associated with sustained expression of the floral repressor gene, FLOWERING LOCUS C (FLC), in an elevated CO 2 -adapted genotype.• Understanding the mechanisms that account for changes in plant developmental timing at elevated [CO 2 ] is critical for predicting the responses of plants to a high-CO 2 world of the near future.

Anthropogenic climate change is projected to alter precipitation patterns, resulting in novel environments for plants. The responses of dominant plant species (e.g. Panicum virgatum L. (switchgrass)) to climate changes can drive broader ecosystem processes such as primary productivity. Using a rainfall mesocosm facility, three ecotypes of P. virgatum (collected from Kansas, Oklahoma and Texas, USA) were subjected to three precipitation regimes (average, -25%, +25%) to determine the physiological and growth responses to altered precipitation in a common garden setting. Results showed mean maximum photosynthetic rates, stomatal conductance, transpiration, midday water potential and dark-adapted chlorophyll fluorescence were lowest in the Kansas ecotypes. Increased precipitation treatments raised the mean midday water potentials and lowered water-use efficiency. Aboveground biomass responded positively to changes in precipitation, but flowering initiation was later and rates were lower for Texas ecotypes. In general, ecotype origin was a better predictor of differences in physiological responses and flowering, whereas the precipitation treatments had greater control over biomass production. Depending on the growth variable measured, these results show responses for P. virgatum are under varying ecotypic or environmental control with few interactions, suggesting that future predictions to climate change need not inherently consider localised adaptations in this economically important and widely distributed species.

Plant morphology and physiology change with growth and development. Some of these changes are due to change in plant size and some are the result of genetically programmed developmental transitions. In this study we investigate the role of the developmental transition, vegetative phase change (VPC), on morphological and photosynthetic changes.• We used overexpression of miR156, the master regulator of VPC, to modulate the timing of VPC in Populus tremula x alba, Zea mays and Arabidopsis thaliana to determine its role in trait variation independent of changes in size and overall age.• Here we find that juvenile and adult leaves in all three species photosynthesize at different rates and that these differences are due to phase-dependent changes in specific leaf area (SLA) and leaf N but not photosynthetic biochemistry. Further, we found juvenile leaves with high SLA were associated with better photosynthetic performance at low light levels..