Relationship between photosynthetic compensation limitation and photoassimilates of maize under heterogeneous light

In natural and field environments, different parts of plants are exposed to various light conditions, such as heterogeneous light. Leaves exposed to more favorable light conditions typically improve the efficiency of plant light energy use by enhancing photosynthesis in heterogeneous light environments, a phenomenon known as the photosynthetic compensation response. Photosynthetic compensation in some plants is limited; however, the biological characteristics and mechanisms involved are unclear. In this study, maize plants with limited photosynthetic compensation were used in a pot experiment. A nylon mesh with a light transmittance of 25% was used to shade maize plants unilaterally and two treatments of homogeneous light (FL) and heterogeneous light (HL) were set up. We compared the anatomical structure, gas exchange characteristics, photosynthetic assimilates, and key synthase contents of unshaded leaves under HL and FL treatments. The results showed that leaf thickness, relative mesophyll cell area, relative bundle sheath cell area, relative bundle area, and vascular sheath-vascular bundle contact area of leaves under the HL treatment were smaller than those under the FL treatment. Meanwhile, the net photosynthetic rate and stomatal conductance of leaves under the HL treatment were lower. In addition, the starch content of the leaves in the HL treatment was lower, the sucrose content was slightly changed, and the sucrose phosphate synthetase content was higher. Therefore, the restriction of photosynthetic compensation under HL treatment is related to the limitation of leaf anatomical structure and stomatal behavior. When photosynthetic compensation was limited, the synthesis of photosynthetic products in the unshaded leaves decreased; though, more photosynthates were allocated to sucrose synthesis. However, owing to morphological and anatomical limitations, the output capacity of leaf sucrose was weak. These results provide a basis for further analyses of the characteristics and mechanisms of plant adaptation to heterogeneous light environments and for breeding varieties suitable for intercropping.