Morphological analysis of plant density effects on early leaf area growth in maize

Abstract

In tillering Gramineae species, leaf-area growth at higher plant densities is limited because no higher-order tillers are formed. This paper analyses the mechanisms of density-related reduced leaf area per plant in non-tillering maize (Zea mays L.). Maize crops with a wide range of plant densities were grown in the field for two years. Half of the plots were shaded (50% transmittance). Detailed measurements of leaf appearance, leaf size, and dry weights of leaves and other plant organs were made. Data were analysed using standard crop-ecological growth functions. Leaf-appearance rates were lower at higher plant densities and under shade. These effects were not caused by the small differences in canopy temperature observed, but closely associated with reductions in the growth rate per individual plant. Leaf length was higher under shade than with full light; effects of plant density on leaf length were inconsistent over the two years, associated with inconsistent effects on leaf-elongation rate. Leaf-elongation duration was longer at higher plant densities in both experimental years. The crop-ecological analysis showed that plant density affected leaf-area expansion of maize mainly through effects on leaf-appearance rates, and that these effects were closely related to density effects on plant-growth rate per leaf-appearance interval.