Abstract

The objective of this study was to determine if low stomatal conductance (g) increases growth, nitrate (NO3) assimilation, and nitrogen (N) utilization at elevated CO2 concentration. Four Arabidopsis (Arabidopsis thaliana) near isogenic lines (NILs) differing in g were grown at ambient and elevated CO2 concentration under low and high NO3 supply as the sole source of N. Although g varied by 32% among NILs at elevated CO2, leaf intercellular CO2 concentration varied by only 4% and genotype had no effect on shoot NO3 concentration in any treatment. Low-gNILs showed the greatest CO2 growth increase under N limitation but had the lowest CO2 growth enhancement under N-sufficient conditions. NILs with the highest and lowest g had similar rates of shoot NO3 assimilation following N deprivation at elevated CO2 concentration. After 5 d of N deprivation, the lowest gNIL had 27% lower maximum carboxylation rate and 23% lower photosynthetic electron transport compared with the highest gNIL. These results suggest that increased growth of low-gNILs under N limitation most likely resulted from more conservative N investment in photosynthetic biochemistry rather than from low g.

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