Elevated CO 2 plus chronic warming reduce nitrogen uptake and levels or activities of nitrogen‐uptake and ‐assimilatory proteins in tomato roots

Atmospheric CO 2 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 3 − ) or ammonium ( NH 4 + ), using membrane‐localized transport proteins in roots, which are key targets for improving N use. Although interactive effects of elevated CO 2 , 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 2 (400 or 700 ppm) and two temperature regimes (30 or 37°C), with NO 3 − or NH 4 + as the N source. Elevated CO 2 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 2 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 2 plus warming, reduced NO 3 − ‐uptake rate per g root was correlated with a decrease in the concentration of NO 3 − ‐uptake proteins per g root, reduced NH 4 + uptake was correlated with decreased activity of NH 4 + ‐uptake proteins and reduced N assimilation was correlated with decreased concentration of N‐assimilatory proteins. These results indicate that elevated CO 2 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).