Discussion
Existing literature has revealed that shading increases leaf senescence, affects plant growth, and decreases crop yield (Gindaba & Midgley, 2005; Spundova et al., 2005). However, different shading patterns, exposure time, the intensity of shade, and tissue position will lead to varied responses by a plant. Until now, the mechanism involved in how partial shading delays leaf senescence in maize remains unclear. In our previous study, the phenotype of delaying maize leaf senescence under narrow-wide row planting patterns in the field was investigated partially (Feng et al., 2020). The cultivation patterns in the field are shown in Supporting Information Figure S4 for a better understanding. Therefore, the present study aimed at providing a detailed mechanism underlying how partial shading delays leaf senescence in maize. Our work is the first report about the synergy in response to shade between two side leaves in maize and how partial shading decreases leaf senescence in maize through increased photosynthetic performance and increased carbon fixation, which finally balances maize yield (Table 2, 3). Our phenotypic data, photosynthetic efficiency, phytohormones synthesis, antioxidants enzyme activity, plant sugar accumulation, carbon activity, and gene expression analysis provided evidence that the partial shading in maize enhances photosynthetic carbon fixation, which delays the leaf senescence resulting in an extended grain-filling period. The phenotypic response of maize plants to different light intensity treatments suggested that full shade induced leaves senescence rapidly compared to partial shading (Supporting Information Figure S1, Table S1), which is consistent with a previous report (Spundova et al., 2005). Partial shade delayed senescence more significantly than the normal light, so we used the normal light treatment as a control to explain the mechanism of partial shade induced delayed senescence in maize.