The Responses of Field-grown Sunflower and Maize to Mechanical Support

The effects of mechanical support on two contrasting speciesof herbaceous annual, the dicot sunflower (Helianthus annuusL.) and the monocot maize (Zea mays L.), were investigated bycomparing the growth and mechanical properties of supportedplants and those which were left to sway freely in the wind. Providing support had its greatest effect on the more highly-stressedbasal areas of the plants, such as the lower stem and the baseof the lateral roots. The diameter of the stem bases of bothspecies was approx. 10% lower in supported plants, but therewas no difference between treatments in the diameter of thestem above 50 cm. Roots of both species also showed a reductionin rigidity and bending strength of 40–50% in the supportedplants compared with freely swaying plants. There was a significantreduction in the partitioning of biomass to the root systemsof supported plants of both species. There were differences in the way in which sunflower and maizeresponded to the provision of support; in sunflower, the reductionin lateral diameter was about twice that in maize, whereas inmaize the decrease in the number of first-order laterals wastwice that of sunflower. This study suggests that thigmomorphogenesismay be a localized response, but that different species canrespond in different ways to mechanical stimulation. Wind; support; anchorage; thigmomorphogenesis; Helianthus annuus L.; sunflower; Zea mays L.; maize