Increased [CO2] does not compensate for negative effects on yield caused by higher temperature and [O3] in Brassica napus L

The 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 [CO2] (700 ppm), temperature (+5 °C) and [O3] (+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 [CO2] increased the vegetative biomass significantly, but seed yield was only significantly enhanced in one of the four cultivars studied. Increased [O3] 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 [CO2], when simultaneously applied in multifactor treatments.

The evaluation of cultivar differences in productivity under elevated [CO2] in combination with increased temperatures and [O3] 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 CO2 and thus counteract the detrimental effects of yield reducing environmental factors such as temperature and O3.