CANOPY STRUCTURE OF MAIZE (ZEA MAYS L.) AT DIFFERENT POPULATIONS : SIMULATION AND EXPERIMENTAL VERIFICATION

GRANT R. F. and HESKETH J. D. Canopy structure of maize (Zea mayz L.) at different populations: simulation and experimental verification. BIOTRONICS 21, 11-24, 1992. Understanding the dynamics of canopy growth is necessary to the understanding and simulation of plant growth in homogeneous populations and of population growth in heterogeneous communities. These dynamics should be studied and reproduced at the organ level of biological organization if they are to be represented at the population level in simulation models. In order to investigate organ growth under a range of conditions, maize (Zea mays L.) was planted at five populations (1.5, 4.3, 5.7, 8.6 and 10.3 plants m~2). Masses and areas of individual leaves, and masses and lengths of individual sheaths and internodes were recorded periodically during canopy growth from the population of 5.7 plants m- 2 . These data were used to parameterize simple algorithms for the expansion of these organs based on their growth in dry mass. These algorithms were then tested on plants hervested at silking from the other populations through the use of a simulation model. Leaf, sheath and internode mass were observed to decrease with higher population, with greater decreases at higher nodes. Specific leaf area (SLA), specific sheath length (SSL) and specific internode length (SNL) were observed to decrease with organ mass, such that reductions at higher populations in organ dimensions were less than those in organ mass. Changes in SLA, SSL and SNL with growth stage and population were reproduced in the model, enabling it to simulate nodal distributions of organ dimensions over time and population. Some uncertainty remains in the estimatiQn of early sheath and internode elongation. A model that can function at this level of temporal and biological organization will be useful in studies of interspecific plant competition, and of insect infestation.