Photosynthetic capacity and assimilate transport of the lower canopy influence maize yield under high planting density.

Photosynthesis is a major trait of interest for development of high-yield crop plants. However, little is known about the effects of high-density planting on photosynthetic responses at the whole-canopy level. Using the high-yielding maize (Zea mays L.) cultivars 'LY66', 'MC670', and 'JK968', we here conducted a two-year field experiment to assess ear development in addition to leaf characteristics and photosynthetic parameters in each canopy layer at four planting densities. Increased planting density promoted high grain yield and population-scale biomass accumulation despite reduced per-plant productivity. MC670 had the strongest adaptability to high-density planting conditions. Physiological analysis showed that increased planting density primarily led to decreases in the single-leaf area above the ear for LY66 and MC670 and below the ear for JK968. Furthermore, high planting density decreased chlorophyll content and the photosynthetic rate due to decreased canopy transmission, leading to severe decreases in single-plant biomass accumulation in the lower canopy. Moreover, increased planting density improved pre-silking biomass transfer, especially in the lower canopy. Yield showed significant positive relationships with photosynthesis and biomass in the lower canopy, demonstrating the important contributions of these leaves to grain yield under dense planting conditions. Increased planting density led to retarded ear development as a consequence of reduced glucose and fructose contents in the ears, indicating reductions in sugar transport that were associated with limited sink organ development, reduced kernel number, and yield loss. Overall, these findings highlighted the photosynthetic capacities of the lower canopy as promising targets for improving maize yield under dense planting conditions.

Improving maize grain yield by matching maize growth and solar radiation.

Matching of maize growth with solar radiation is of great importance for achieving high yield. We conducted experiments using different maize cultivars and planting densities under different solar radiations during grain filling to quantitatively analyze the relationships among these factors. We found that a decrease in solar radiation after silking caused a drop in maize grain yield and biomass, with lower solar radiation intensities leading to worse grain yields and biomass. Cultivar ZD958 was more sensitive to solar radiation changes than cultivar XY335; slight decreases in solar radiation (i.e., 15% shading) caused significant declines in ZD958 grain yield. When total solar radiation during grain filling was less than 486.9 MJ m-2 for XY335 and less than 510.9 MJ m-2 for ZD958, the two cultivars demonstrated high yields at lower planting density of 7.5 × 104 plants ha-1; average yields were 13.36 and 11.09 Mg ha-1, respectively. When radiation intensities were higher than 549.5 MJ m-2 for XY335 and higher than 605.8 MJ m-2 for ZD958, yields were higher at a higher planting density of 12 × 104 plants ha-1, with average yields of 20.58 Mg ha-1 for XY335 and 19.65 Mg ha-1 for ZD958.