Effect of Nitrogen and Shade on Photosynthetic Gas Exchange and Productivity of Wheat Under Elevated Atmospheric CO2 Concentration

Abstract

Sufficient nitrogen and shade may benefit photosynthetic down-regulation at elevated CO2 concentrations. Two levels of atmospheric CO2 400 and 760 μmol mol−1 were simulated using controlled environment open-top chambers, wheat (Triticum aestivum L) was grown at two N application rates (0 and 200 mg N kg−1 soil), and two photosynthetic photon fluxes (PPF, 100 and 60 % of solar irradiance). The increasing leaf N concentration, shade and N application extended the wheat developmental period and increased flag leaf fresh mass, water content, plant height and spike length by 11 d, 125, 126, 29 and 43 %, respectively. However, with sufficient N and elevated CO2, shade decreased dry mass, kilo-grain weight, instantaneous water use efficiency, grain water use efficiency and photosynthetic N use efficiency was increased by 30, 12, 2, 36 and 44 %, as compared with the unshaded treatment. Higher N application and shade increased N and chlorophyll concentration in flag leaves by 135 and 35 %, resulting in extended growth stage and increased plant and leaf water content, caused significant increments of plant height, grain number per spike and grain weight per spike under elevated CO2 as compared to N-deprived (0 mg N kg−1 soil) and unshaded treatment. Shade significantly increased leaf and plant water content, but did not affect wheat water and nitrogen use efficiency, which indicated that the decline of water content in flag leaves was a response of wheat to elevated CO2. The increment of leaf water status may extend the growth period to relieve photosynthesis acclimation at elevated CO2.