We investigated the effect of elevated [CO2], [O3] and temperature on plant productivity and if these climate factors interacted with each other in multifactor treatments. The climate effects were studied in 14 different cultivars/lines of European spring oilseed rape (Brassica napus L.) and spring barley (Hordeum vulgare L.). Seven genotypes of each species were cultivated in six single‐ and multifactor treatments with ambient or elevated CO2 (385 ppm and 700 ppm), O3 (20 ppb and 60 ppb) and temperature (12/19 °C and 17/24 °C). Growth and production parameters were measured. Elevated CO2 increased yield and biomass. Seed number increased by about 47 % in barley and by 26 % in oilseed rape, but in oilseed rape, the TSW was significantly decreased, possibly because of shortening of the seed filling period. Higher temperatures decreased yield and biomass significantly in both species. A significantly decreased yield and thousand grain weight was also seen in barley due to elevated O3. The multifactor combination of elevated CO2, O3 and temperature showed a decrease in growth and production in the two species, though not statistically significant for all parameters. This trend suggests that the expected increase in the plant production in northern Europe, indicated by Intergovernmental Panel on Climate Change (IPCC) as a consequence of increased [CO2] and temperature, may not hold, due to interactions between these abiotic factors.

a b s t r a c tThe projected changes of atmospheric composition and associated climatic parameters will challenge the agricultural production in ways, which existing crop populations have not previously experienced. Therefore, understanding the responsiveness to changes of multiple environmental parameters in existing genotypes is vital. In this study, the responses in yield and biomass production of four different cultivars of oilseed rape (Brassica napus L.) were tested under five different combinations of increased [CO 2 ] (700 ppm), temperature (+5• C) and [O 3 ] (+40 ppb). Especially the multifactor treatments are relevant for predictions of the future production, as they mimic the multidimensional environmental changes that are expected within this century. All treatments were given the same amount of water, which mimicked future limited water availability e.g. in treatments with elevated temperature.The biomass and yield parameters were found to be significantly cultivar dependent. However, in all cultivars elevated temperature caused a significant reduction in yield parameters, while biomass was not affected significantly. Elevated [CO 2 ] increased the vegetative biomass significantly, but seed yield was only significantly enhanced in one of the four cultivars studied. Increased [O 3 ] did not have significant effects on any of the cultivars. In general, the negative effects of a 5• C temperature elevation on yield could not be compensated by elevated [CO 2 ], when simultaneously applied in multifactor treatments. The evaluation of cultivar differences in productivity under elevated [CO 2 ] in combination with increased temperatures and [O 3 ] is necessary to derive at a realistic prediction for the future food and biomass production and for the selection of cultivars providing an adaptation potential to environmental change. Our results suggest that future breeding of B. napus should be based on old cultivars, since more modern varieties seem to have lower potentials to respond to CO 2 and thus counteract the detrimental effects of yield reducing environmental factors such as temperature and O 3 .

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Functional plant traits are likely to adapt under the sustained pressure imposed by environmental changes through natural selection. Employing Brassica napus as a model, a multi-generational study was performed to investigate the potential trajectories of selection at elevated [CO2] in two different temperature regimes. To reveal phenotypic divergence at the manipulated [CO2] and temperature conditions, a full-factorial natural selection regime was established in a phytotron environment over the range of four generations. It is demonstrated that a directional response to selection at elevated [CO2] led to higher quantities of reproductive output over the range of investigated generations independent of the applied temperature regime. The increase in seed yield caused an increase in aboveground biomass. This suggests quantitative changes in the functions of carbon sequestration of plants subjected to increased levels of CO2 over the generational range investigated. The results of this study suggest that phenotypic divergence of plants selected under elevated atmospheric CO2 concentration may drive the future functions of plant productivity to be different from projections that do not incorporate selection responses of plants. This study accentuates the importance of phenotypic responses across multiple generations in relation to our understanding of biogeochemical dynamics of future ecosystems. Furthermore, the positive selection response of reproductive output under increased [CO2] may ameliorate depressions in plant reproductive fitness caused by higher temperatures in situations where both factors co-occur.