Response of some physiological parameters of sunflower (Helianthus annus L.) to variation in the light environment

Abstract

Light is considered as an important source of energy for all types of plants, and any change in its quality or quantity such as R:FR ratio affects plant growth through physiological, morphological, and biochemical processes. To examine the impact of changes in light quality on sunflower canopy, a factorial experiment with three replications was conducted at the Research Farm of Faculty of Agriculture, University of Birjand, in spring and summer 2014. The treatments included planting density (5 and 10 plants per square meter), leaf arrangement (no defoliation, and defoliating 50% of leaves of each plant when heads became visible), and the colors of optical filters wrapped around the shoot (blue cellophane with R:FR = 1.84 passing blue spectrum with the wavelength 480.62 nm, white cellophane as a control treatment for the blue one with R:FR = 2.40 which transmit the whole spectrum contained in the sunlight, and a control where no filter was used). The use of blue filters resulted in greater stem elongation, reduced stem diameter, and reduced amounts of plant dry matter allocated to each sunflower head as well as the achene number per capitulum. Blue filters had no significant impact on 100-grain weight. During the growing period, reduction in the dry matter allocated to stem was smaller when blue filters were used, especially for the defoliation treatments, compared to where no filter or white filters were used. Defoliation in combination with using blue filters at a density of 5 plants m-2 increased specific leaf area (SLA) due to larger leaf areas. It seems any variation in R:FR, plant density, and/or leaf density can influence sunflower yield through affecting photo-morphological processes.