Influence of elevated CO2 and nitrogen nutrition on photosynthesis and nitrate photo‐assimilation in maize (Zea mays L.)

• Published in: Plant, cell and environment cell and environment, 2003-09, Vol.26 (9), p.1525-1530
• Main Authors: COUSINS, A. B., BLOOM, A. J.
• Format: Article
• Language: English
• Subjects: Animal, plant and microbial ecology; Applied ecology; assimilatory quotient; Biological and medical sciences; carbon assimilation; chlorophyll fluorescence; Ecotoxicology, biological effects of pollution; Effects of pollution and side effects of pesticides on plants and fungi; electron transport; Fundamental and applied biological sciences. Psychology; oxygen exchange; Zea mays
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1046/j.1365-3040.2003.01075.x

ABSTRACT Measurements of CO2 and O2 gas exchange and chlorophyll a fluorescence were used to test the hypothesis that elevated atmospheric CO2 inhibits nitrate (NO3–) photo‐assimilation in the C4 plant, maize (Zea mays L.). The assimilatory quotient (AQ), the ratio of net CO2 assimilation to net O2 evolution, decreases as NO3– photo‐assimilation increases so that the difference in AQ between the ammonium‐ and nitrate‐fed plants (ΔAQ) provided an in planta estimate of NO3– photo‐assimilation. In fully expanded maize leaves, NO3– photo‐assimilation was detectable only under high light and was not affected by CO2 treatments. Furthermore, CO2 assimilation and O2 evolution were higher under NO3– than ammonia (NH4+) regardless of CO2 levels. In conclusion, NO3– photo‐assimilation in maize primarily occurred at high light when reducing equivalents were presumably not limiting. Nitrate photo‐assimilation enhanced C4 photosynthesis, and in contrast to C3 plants, elevated CO2 did not inhibit foliar NO3– photo‐assimilation.