Improved photosynthetic performance under unilateral weak light conditions in a wide–narrow-row intercropping system is associated with altered sugar transport.

The article investigates how unilateral weak light affects photosynthesis and sugar metabolism in maize (Zea mays) under wide–narrow-row intercropping systems, particularly maize–soybean relay intercropping. It finds that unshaded maize leaves exhibit increased net photosynthetic rates (Pn) as shading on the opposite side intensifies, accompanied by decreased sucrose and starch concentrations due to enhanced sugar export to grains. Gene expression analyses reveal that specific genes related to sucrose and starch metabolism and transport (e.g., Sweet13a, Sut1, Agpsl1, Bmy, Mex1-like) are differentially regulated in shaded versus unshaded leaves, supporting altered sugar allocation under unilateral shading. The study concludes that improved photosynthetic performance in unshaded leaves under unilateral weak light is linked to increased sugar transport to grains, and recommends a narrow-row spacing of 40 cm to optimize unilateral shading, maintain yield, and enhance land use efficiency in intercropping systems.