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CORN

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

^a South Dakota State Univ., Plant Science Dep., Brookings, SD 57007
^b USDA-ARS, Biosciences Research Lab., Fargo, ND, 58105
^c Michigan State Univ. Ext., Rogers City, MI. 49779

^* Corresponding author (sharon.clay{at}sdstate.edu).

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 ¹³C isotopic discrimination () 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 C₄ 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.

Abbreviations: NIR, near-infrared • PEPCK, phosphoenolpyruvate carboxykinase • PEPC, phosphoenolpyruvate carboxylase • PPDK, pyruvate orthophosphate dikinase • PCR, real-time polymerase chain reaction, real-time • 2x, 149,000 plants ha^–1 • 1x, 74,500 plants ha^–1

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Received for publication December 2, 2008.