Corn Response to Competition: Growth Alteration vs. Yield Limiting Factors

Competition mechanisms among adjacent plants are not well understood. This study compared corn growth and yield responses to water, N, and shade at 74,500 plants ha(-1) (1x) with responses to water and N when planted at 149,000 plant ha(-1). Plant biomass, leaf area, chlorophyll content, reflectance, and enzyme expression (transcriptome analysis) were measured at V-12. Grain and stover yields were measured with grain analyzed for C-13 isotopic discrimination (A) and N concentration. At V-12, 60% shade plants had increased chlorophyll and reduced leaf area and height compared to full sun plants. In the 2x treatment, plants had 11% less chlorophyll than 1x plants with leaf area and height similar to 60% shade plants. At harvest, plants in the 2x treatment were smaller, had increased water and N use efficiency, and an 11% per hectare yield increase compared with the 1x unstressed treatment. Per-plant yields from 60% shade and 2x treatments were 50% less than 1x unstressed treatment. Yield reduction in shaded plants was attributed to light stress. Lower yield in the 2x treatment was attributed to a population-density induced 20% decrease in the red/near-infrared (NIR) ratio,which resulted in downregulation of C-4 carbon metabolism enzymes (phosphoenolpyruvate carboxykinase, phosphoenolpyruvate carboxylase, and pyruvate orthophosphate dikinase). Although the net impact of high plant density and shade stress on per-plant yield were similar, the stress compensation mechanisms differed.