Competition for light and nitrogen with an earlier-sown species negatively affects leaf traits and leaf photosynthetic capacity of maize in relay intercropping

Mixing crop species in intercrops often results in yield advantages but the underlying processes are not completely understood. Increased resource capture in intercrops, particularly of light and nutrients, has been frequently demonstrated, but there is less information on the effect of intercropping on the photosynthetic capacity of leaves and on the leaf traits related to photosynthesis. Here we determine whether photosynthetic capacity and associated leaf traits are enhanced in intercropped maize (Zea mays L.), a species frequently used in intercrops. We determined leaf photosynthetic capacity (A1800) and leaf traits of maize leaves in different canopy layers and at different growth stages in relay strip intercrops with spring wheat (Triticum aestivum L.) or faba bean (Vicia faba L.) and in the maize sole crop. We also measured the distribution of photosynthetically active radiation (PAR) in the canopies. Intercropping with wheat or faba bean resulted in larger specific leaf area (SLA; thinner leaves), lower specific leaf nitrogen (SLN), and lower A1800 of maize leaves during vegetative growth, and differences were larger for maize intercropped with faba bean than wheat, consistent with stronger shading by faba bean than wheat. After the harvest of companion species, maize leaves received more light in the two intercrops than in the sole maize crop, but this did not result in increases in leaf N concentration, SLN, and A1800. Results indicate that shading and lower leaf N caused by relay intercropping maize with an earlier sown species negatively affected leaf photosynthetic capacity of maize leaves. The yield increase of maize in relay intercrops was not due to a higher leaf photosynthetic capacity. Options for mitigating or overcoming these negative intercropping effects are discussed.