Photosynthetic Induction Under Fluctuating Light Is Affected by Leaf Nitrogen Content in Tomato

The response of photosynthetic CO₂ assimilation to changes of illumination affects plant growth and crop productivity under natural fluctuating light conditions. However, the effects of nitrogen (N) supply on photosynthetic physiology after transition from low to high light are seldom studied. To elucidate this, we measured gas exchange and chlorophyll fluorescence under fluctuating light in tomato (Solanum lycopersicum) seedlings grown with different N conditions. After transition from low to high light, the induction speeds of net CO₂ assimilation (A ), stomatal conductance (g ), and mesophyll conductance (g ) delayed with the decline in leaf N content. The time to reach 90% of maximum A , g and g was negatively correlated with leaf N content. This delayed photosynthetic induction in plants grown under low N concentration was mainly caused by the slow induction response of g rather than that of g . Furthermore, the photosynthetic induction upon transfer from low to high light was hardly limited by photosynthetic electron flow. These results indicate that decreased leaf N content declines carbon gain under fluctuating light in tomato. Increasing the induction kinetics of g has the potential to enhance the carbon gain of field crops grown in infertile soil.