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

Atmospheric CO 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 (NO ) or ammonium (NH ), using membrane-localized transport proteins in roots, which are key targets for improving N use. Although interactive effects of elevated CO , 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 CO (400 or 700 ppm) and two temperature regimes (30 or 37°C), with NO or NH as the N source. Elevated CO 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 CO 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 CO plus warming, reduced NO -uptake rate per g root was correlated with a decrease in the concentration of NO -uptake proteins per g root, reduced NH uptake was correlated with decreased activity of NH -uptake proteins and reduced N assimilation was correlated with decreased concentration of N-assimilatory proteins. These results indicate that elevated CO 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).