Effects of sowing date, photoperiod and nitrogen on variation in main culm leaf dimensions in field-grown wheat

Abstract

In some cereal simulation models, canopy leaf area development is calculated using relationships that summarize how leaf size changes with position. The nature and extent to which various environmental factors interact with ontogenetic variations in leaf size, however, is not clearly understood. This study was undertaken, therefore, to evaluate how temperature, photoperiod and nitrogen impact on leaf to leaf relationships in wheat grown under field conditions. Four contrasting genotypes of wheat comprising two spring and two unvernalized winter types were sown on five dates, supplied with one of two levels of nitrogen (150 kg N ha−1 and 0 kg N ha−1), and grown under natural and extended photoperiod conditions. For the spring wheats, individual mature leaf area increased along with leaf number up to leaf 5 (a stage that coincided with rapid stem elongation) but varied for subsequent leaves in a manner that was dependent on genotype and environment.In the period prior to the expansion of the fifth leaf, neither nitrogen nor photoperiod significantly influenced the pattern of change in leaf size. Thereafter, leaves under low nitrogen and extended photoperiod progressively became smaller, an effect that was due primarily to changes in length rather than in width. For the winter genotypes, which did not reach the stage of rapid stem elongation, mature leaf dimensions increased along with leaf number during the whole period of study and were not markedly affected by photoperiod but, after leaf 5, were smaller for the low nitrogen level. For all genotypes, the size of the first leaf and the coefficients derived by regressing the area of successive leaves on the area of the previous leaf during the vegetative phase varied among sowing dates due partly to the temperature environment under which the leaves at each node developed. The results, however, indicated that the potential leaf size at any of the lowermost leaf positions can be obtained by using a logarithmic function that relates the potential size of one leaf to its predecessor. Such relationship can be used to calculate actual leaf size if account is taken of environmental and assimilate supply factors that operate during leaf expansion. Key words: Wheat, sowing date, leaf area, temperature, photoperiod