S13 - Session O3 - Nitrogen form mediates resource allocation and growth of the C3 plant radish with well-balanced sink-source relationship under elevated CO2

Authors: Jana Zinkernagel *, Madita Lauer, Maximilian Koppel, Samantha Rubo, Lilian Schmidt

Elevated carbon dioxide concentrations in the atmosphere (eCO 2 ) may alter plant physiological processes and therefore yield and quality characteristics of vegetable crops. In crops with C3 carbon fixation, root crops showed highest yield response under eCO 2 which is suggested to be linked to their large sink strength. The high C gain under eCO 2 can be limited by processes that constrain sink capacity, such as nitrogen (N) supply. The form and amount of N compounds allocated in source organs have considerable effects on N transport and partitioning to sinks, and thus sink growth. This study used radish ( Raphanus sativus ), which is known to have a high sink strength, to elucidate the interaction of N form and eCO 2 in root vegetables. Radish plants were grown in climate chambers at 400 ppm (aCO 2 ) and 1000 ppm CO 2 (eCO 2 ) with either pure nitrate or ammonium-dominated N. A split plot design was applied. Plants were harvested after four weeks and physiological, morphological and chemical parameters were assessed in leaves and tubers, respectively. Neither CO 2 level nor N form affected the photosynthetic CO 2 assimilation. However, plants grown under eCO 2 had more aboveground biomass. The increased C/N ratio in leaves indicate that photoassimilates were accumulated in the foliage, but due to the large sink strength of the growing tuber, no feedback inhibition of photosynthetic CO 2 assimilation occurred. Consequently, the tubers showed higher volume, fresh and dry mass when grown under eCO 2 . This was especially true for plants that received ammonium-dominated N, suggesting that this fertilization strategy further enhanced tuber growth under eCO 2 at the expense of leaf area. When supplied with pure nitrate, the foliage of radish plants represented a stronger sink for photoassimilates and thus reduced the investment of resources into tubers. Radish therefore will benefit from eCO 2 , especially when being supplied with ammonium-dominated N fertilizer.