Elevated CO2 plus chronic warming reduce nitrogen uptake and levels or activities of nitrogen-uptake and -assimilatory proteins in tomato roots

Atmospheric CO2 enrichment is expected to often benefit plant growth, despite causing global warming and nitrogen (N) dilution in plants. Most plants primarily procure N as inorganic nitrate (NO3-) or ammonium (NH4+), using membrane-localized transport proteins in roots, which are key targets for improving N use. Although interactive effects of elevated CO2, chronic warming and N form on N relations are expected, these have not been studied. In this study, tomato (Solanum lycopersicum) plants were grown at two levels of CO2 (400 or 700ppm) and two temperature regimes (30 or 37 degrees C), with NO3- or NH4+ as the N source. Elevated CO2 plus chronic warming severely inhibited plant growth, regardless of N form, while individually they had smaller effects on growth. Although %N in roots was similar among all treatments, elevated CO2 plus warming decreased (1) N-uptake rate by roots, (2) total protein concentration in roots, indicating an inhibition of N assimilation and (3) shoot %N, indicating a potential inhibition of N translocation from roots to shoots. Under elevated CO2 plus warming, reduced NO3--uptake rate per g root was correlated with a decrease in the concentration of NO3--uptake proteins per g root, reduced NH4+ uptake was correlated with decreased activity of NH4+-uptake proteins and reduced N assimilation was correlated with decreased concentration of N-assimilatory proteins. These results indicate that elevated CO2 and chronic warming can act synergistically to decrease plant N uptake and assimilation; hence, future global warming may decrease both plant growth and food quality (%N).