Quantifying the effect of soil water deficit on transpiration, growth, development, and quality of cut sunflower

Abstract Water deficit is a major abiotic factor limiting the growth, development, and yield of cut sunflowers (Helianthus annuus L.). The Fraction of Transpirable Soil Water (FTSW) is a reliable approach to assess plant responses to soil water deficit and determine stomatal closure thresholds. The objective in this study was to quantify the effects of soil water deficit on plant transpiration, growth, development, and quality of cut sunflower using the Fraction of Transpirable Soil Water (FTSW) approach. A pot experiment was conducted under controlled conditions with two treatments: no deficit and deficit, applied during the reproductive phase. The results showed that water deficit reduced stem length (96.9 cm to 87.5 cm), stem diameter (0.86 cm to 0.59 cm), and capitulum diameter (5.5 cm to 4.0 cm). Dry biomass of roots, stems, leaves, and capitulum were also negatively affected by water deficit, confirming the sensitivity of cut sunflower to soil water availability. The threshold FTSW for transpiration was estimated at 0.62, indicating the onset of stomatal closure. These findings agree with previous studies on gladiolus and chrysanthemum, reinforcing similarities in stomatal regulation among ornamental species. Efficient water management based on FTSW is essential to mitigate the negative effects of water deficit and maintain the commercial quality of cut sunflowers. The FTSW approach proved to be a valuable tool for sustainable management in ornamental horticulture and can be adapted for other species grown under water-limiting conditions.