C and N allocation on wheat under the effects of depleted, current and elevated [CO2] are modulated by water availability

• Using long-term treatments with different CO 2 concentrations (depleted, current, and elevated) and water availability (well-watered and mild water stress), as well as short-term labelling with 13 C and 15 N in wheat durum plants, we found the following: • The plant's response to different environmental [CO 2 ] was modulated by water availability, and therefore, C and N allocation was also modulated by both factors. • The physiological plant response was acclimation to different environmental CO 2 was modulated by water availability; the photosynthetic acclimation affected the C and N allocation in plants. However, this acclimation was broken during grain filling changing the C and N allocation in our plants. • Plants under depleted [CO 2 ] presented lower drought resistance than those under the current [CO 2 ]. Plants under elevated [CO 2 ] conditions presented higher drought resistance than those in the current [CO 2 ]. • However, the mechanisms controlling whole C and N plant acquisition and allocation under different climatic scenarios with environmental stresses in wheat plants are not completely clear and require further studies. Although elevated atmospheric [CO 2 ] has substantial indirect effects on vegetation carbon uptake via associated climate change, their dynamics remain unclear. The carbon and nitrogen allocation and partitioning in durum wheat were compared at different [CO 2 ] and different water availability. The aim of this study was to investigate how the impacts of depleted and elevated [CO 2 ] driven climate change on Mediterranean wheat plants under drought conditions. For that reason, double stable isotope labelling using 13 CO 2 and 15 NH 4 - 15 NO 3 was conducted to follow 13 C and 15 N allocation and partitioning in the different plant organs. Plants were studied in growth chambers under three different CO 2 environments (depleted, current and elevated) and two water availability conditions (well-watered and mild-water-stress). Isotopic 13 C and 15 N determination, gas exchange analyses and growth parameters were measured. We show that plants subjected to depleted and elevated [CO 2 ] suffered up and down regulation of photosynthesis respectively, but their responses were both modulated by water availability. Depleted [CO 2 ] and drought reduced plant biomass. However, elevated [CO 2 ], show that the initial positive effect of elevated [CO 2 ] on carbon uptake declined rapidly, showing a consequence of physiological acclimation and the inhibition of [Rubisco] and activity, this effect was more evident in combination with drought. In both cases, depleted [CO 2 ] and elevated [CO 2 ] condition modified the C and N allocation compared with current [CO 2 ], overall combined with drought. These results obtained highlight the different C and N management strategies of wheat and provide relevant information about the potential response of plants under global climate change conditions.