Summary• Reproductive traits are key characteristics for predicting the response of communities and ecosystems to global change.• We used meta-analysis to integrate data on eight reproductive traits from 159 CO 2 enrichment papers that provided information on 79 species.• Across all species, CO 2 enrichment (500 -800 µl l − 1 ) resulted in more flowers (+19%), more fruits (+18%), more seeds (+16%), greater individual seed mass (+4%), greater total seed mass (+25%), and lower seed nitrogen concentration, (N) ( − 14%). Crops and undomesticated (wild) species did not differ in total mass response to elevated CO 2 (+31%), but crops allocated more mass to reproduction and produced more fruits (+28% vs +4%) and seeds (+21% vs +4%) than did wild species when grown at high CO 2 . Seed [N] was not affected by high CO 2 concentrations in legumes, but declined significantly in most nonlegumes.• Our results provide robust estimates of average plant reproductive responses to CO 2 enrichment and demonstrate important differences among individual taxa and among functional groups. In particular, crops were more responsive to elevated CO 2 than were wild species. These differences and the substantial decline in seed [N] in many species have broad implications for the functioning of future natural and agroecosystems.© New Phytologist (2002) 156 : 9 -26

Reproduction is an important life history trait that strongly affects dynamics of plant populations. Although it has been well documented that elevated carbon dioxide (CO2) in the atmosphere greatly enhances biomass production in plants, the overall effect of elevated CO2 on reproductive allocation (RA), i.e., the proportion of biomass allocated to reproductive structures, is little understood. We combined meta-analysis with graphical vector analysis to examine the overall effect of elevated CO2 on RA and how other environmental factors, such as low nutrients, drought and elevated atmospheric ozone (O3), interacted with elevated CO2 in affecting RA in herbaceous plants. Averaged across all species of different functional groups and environmental conditions, elevated CO2 had little effect on RA (-0.9%). RA in plants of different reproductive strategies and functional groups, however, differed in response to elevated CO2. For example, RA in iteroparous wild species decreased by 8%, while RA in iteroparous crops increased significantly (+14%) at elevated CO2. RA was unaffected by CO2 in plants grown with no stress or in low-nutrient soils. RA decreased at elevated CO2 and elevated O3, but increased in response to elevated CO2 in drought-stressed plants, suggesting that elevated CO2 could ameliorate the adverse effect of drought on crop production to some extent. Our results demonstrate that elevated CO2 and other global environmental changes have the potential to greatly alter plant community composition through differential effects on RA of different plant species and thus affect the dynamics of natural and agricultural ecosystems in the future.

The relationships between the responses to elevated CO, of the vegetative and reproductive phase were investigated in radish, used as a test system. The hypothesis that an increase in nonfoliar vegetative storage capacity promotes reproductive output was tested. Three cultivars of Raphanus sativus and the wild, Raphanus raphanistrum, differing in root to shoot ratios, were grown under two levels of CO? and two levels of nitrogen fertilization. Varieties possessed different strategies of carbon storage and showed distinct responses to CO, at each vegetative harvest time. Vegetative sinks of hypocotyls, petioles, and young blades were enhanced by CO,. Nitrogen promoted vegetative shoot growth, but did not enhance the reproductive response to CO,. By the end of the reproductive phase, varieties did not differ in total biomass. Reproductive response to CO, may have been limited by the lack of an effect on the timing of flowering. Correlations in C0, enhancement ratios were examined in 12 traits of each phase. Only vegetative total leaf area correlated with reproductive mass. Foliar starch correlated with decreased abortion. Enhancements in vegetative biomass did not correlate with any reproductive response. Detailed studies of the reproductive phase are needed to understand the whole-plant response to elevated CO,.Resume : L'auteure a CtudiC les relations entre les rCactions auz teneurs ClevCes en CO, de la phase vCgCtative et de la phase reproductive, en utilisant le radis comme modble. Elle a vCrifiC l'hypothbse qu'une augmentation de la capacitC d'accumulation de rCserves dans un organe vCgCtatif non-foliaire promeut l'effort de reproduction. Elle a cultivC, en presence de deux teneurs en CO, et de deux niveaux de fertilisation azotee, trois cultivars de Raphanus sativus ainsi que le radis sauvage Raphanrts rclphanistrum, diffkrents par leurs rapports racine B tige. Les variCtCs posskdent diffkrentes stratCgies pour accumuler le carbone et montrent des reactions diffkrentes au CO, B chaque Ctape du dCveloppement vCgCtatif. Les puits vCgCtatifs des hypocotyles, des pCtioles et des jeunes limbes augmentent sous l'influence du CO,. L'azote stimule le dCveloppement vCgCtatif de la tige, mais n'augmente pas la rCaction de la reproduction sous l'influence de CO, accru. Vers la fin de la phase reproductive, les variCtCs ne montrent pas de diffirence dans leur biomasse totale. La reaction de la reproduction au C 0 2 pourrait avoir Ct C limitCe par le manque d'un effect sur le moment de la floraison. L'auteure a examine les corrClations entre les rapports d'augmentation du CO, selon 12 caractbres pour chaque phase. Seule la surface foliaire vegetative totale montre une corrklation avec la masse reproductrice. L'amidon foliaire est reliC avec une diminution de I'avortement. L'augmentation de la biomasse vCgCtative n'est pas corrClCe avec la rCaction reproductive. Pour comprendre la reaction de la plante entibre au CO, ClevC, il faudra entreprendre des Ctudes dCtaillCes de la phase de reproduction.

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