Effects of elevated CO₂ on leaf area dynamics in nodulating and non-nodulating soybean stands

Aims: The effects of elevated CO₂ on leaf area index (LAI) vary among studies. We hypothesized that the interactive effects of CO₂ and nitrogen on leaf area loss have important roles in LAI regulation. Methods: We studied the leaf area production and loss using nodulating soybean and its non-nodulating isogenic line in CO₂-controlled greenhouse systems. Results: Leaf area production increased with elevated CO₂ levels in the nodulating soybean stand and to a lesser extent in the non-nodulating line. Elevated CO₂ levels accelerated leaf area loss only in nodulating plants. Consequently, both plants exhibited a similar stimulation of peak LAI with CO₂ elevation. The accelerated leaf loss in nodulating plants may have been caused by newly produced leaves shading the lower leaves. The nodulating plants acquired N throughout the growth phase, whereas non-nodulating plants did not acquire N after flowering due to the depletion of soil N. N retranslocation to new organs and subsequent leaf loss were faster in non-nodulating plants compared with nodulating plants, irrespective of the CO₂ levels. Conclusion: LAI regulation in soybean involved various factors, such as light availability within the canopy, N acquisition and N demands in new organs. These effects varied among the growth stages and CO₂ levels.