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

Author
item CLAY, SHARON - South Dakota State University
item CLAY, DAVID - South Dakota State University
item Horvath, David
item PULLIS, J - Michigan State University
item CARLSON, C - South Dakota State University
item HANSEN, S - South Dakota State University
item REICKS, G - South Dakota State University

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2009
Publication Date: 10/6/2009
Citation: Clay, S.A., Clay, D.E., Horvath, D.P., Pullis, J., Carlson, C.G., Hansen, S., Reicks, G. 2009. Corn Response to Competition: Growth Alteration vs. Yield Limiting Factors. Agronomy Journal. 101:1522-1529. DOI:10.2134/agronj2008.0213x

Interpretive Summary: This paper defines the impact of overcrowding and shading of corn plants by physical (yield, plant growth etc.), physiological (nitrogen and water use) and molecular (changes in gene expression) means. This work demonstrated that despite similarities in physical impacts of both over-crowding and shade were similar; the mechanisms by which these two stresses impact plant growth are different and implicate key differences in how the plants experiencing these stresses use CO2.

Technical Abstract: Understanding competition mechanisms among adjacent plants can improve site-specific management recommendations. This 2-yr study compared two hypotheses, yield limiting factors vs. behavior modification, to explain plant interactions. Corn was grown under different levels of stress by varying light intensity (0; 40; and 60% shade), population density [74,500 (1X); 149,000 (2X) plants ha-1], and water (rainfall; rainfall + irrigation) and N (0; 228 kg N ha-1) availability. Plant biomass, leaf area, and chlorophyll content were measured at V12 in 2005 and 2006 with 2006 leaf samples from selected treatments used for transcriptome analysis. At maturity, grain, stover, cob and soil water and inorganic N were measured. Grain was analyzed for 13C isotopic discrimination (Ä) and N concentration. At V-12, compared to 1X full-sun plants, shade increased chlorophyll content by 6% and reduced leaf area and height by 10 and 15%, respectively; whereas 2X treatment decreased chlorophyll by 11%. Transcriptome analysis indicated that key enzymes involved in C4 carbon metabolism, phosphoenolpyruvate carboxykinase, phosphoenolpyruvate carboxylase, and pyruvate orthophosphate dikinase, were down-regulated in the 2X treatment relative to amounts in 60% shade. Plants under shade or in 2X populations had 50% less grain yield plant-1 than 1X plants. Based on Ä and transcriptome analyses, yield reduction in shade was attributed to light stress, however, yield reduction in the 2X treatment appeared to be due to a series of events that included sensing a high plant density during the critical weed free period and down-regulating key enzymes involved in C4 metabolism which led to smaller plants and increased water and N use efficiency. These data indicate that although the net impact of density and shade stress on yield was similar, mechanisms to counteract these stresses differed.