Plant morphology, environment and leaf area growth in wheat and maize

Leaf area expansion of wheat (Triticum aestivum L.) and maize (Zea mays L.) plants, as contrasting representatives of the Gramineae family, was analysed. Seven variables were identified that together completely determine leaf area expansion of the plant: leaf appearance rate per tiller, specific site usage (fraction of buds that ultimately develop into a visible tiller at a specific site), Haun Stagedelay (indicating the timing of tiller appearance relative to the parent tiller), leaf elongation rate, leaf elongation duration, maximum leaf width and a leaf shape variable. Experiments with spaced plants in growth chambers yielded equations in which the effects of leaf and tiller position, temperature and photosynthetic photon flux density (PPFD) were quantified for each leaf area variable. In non-tillering species maize, leaf appearance rate and leaf elongation rate were higher, and leaf elongation duration was shorter at higher temperatures. At higher PPFD values, leaf appearance rate and maximum leaf width were higher and leaf elongation rate was lower. In wheat, the effects of temperature and PPFD were qualitatively equal to those in maize, except that there was no effect of PPFD on maximum leaf width. In the tillering species wheat, specific site usage was higher at lower temperatures and higher PPI'D values. Equations were developed for the effects of leaf position on leaf elongation rate and maximum leaf width. This knowledge was used in the analysis of effects of plant density in growth chamber and field experiments. Plant density mainly affected leaf appearance rate in maize and specific site usage in wheat. For both species, the effects of plant density on these variables seemed well related to local assimilate availability. Based upon the morphological framework presented, a simulation model was developed for wheat using the principles of object orientation. Plant related processes were strictly simulated at organ level. The simulation results showed clear differences in leaf area expansion for leaves at different positions in the plant. The morphological framework can be used for experimental analysis of leaf area growth, revealing mechanisms regulating leaf area growth of plants. The simulation model is flexible and can be easily extended for different environmental conditions and plant species.