1 Section for Crop Sciences, Department of Plant and Environmental Sciences, Faculty of Science, Københavns Universitet2 Shenyang Agricultural University3 Chinese Academy of Sciences4 Shenyang Agricultural University5 Section for Crop Sciences, Department of Plant and Environmental Sciences, Faculty of Science, Københavns Universitet
Potted ornamental plants are often exposed to drought stress during shipping and retailing, which decreases the value and postharvest quality. Thus, selection of genotypes which can better withstand soil water deficits is essential for sustainable production. Here, the response of three genotypes of potted Campanula medium (denoted as G100, G102 and G104) to progressive soil drying was investigated and their post-production performance was evaluated for four weeks. The potted plants were grown in a climate controlled greenhouse and were either well-watered (W) or drought-stressed (D) at floral bud formation stage. Soil water status was expressed as the fraction of transpirable soil water (FTSW). In the D pots, FTSW declined fastest in G100, followed by G102, and slowest in G104 after withholding irrigation. In the W plants, stomatal conductance (gs) was similar among the three genotypes, whereas transpiration rate (T) differed significantly among genotypes and was highest for G100, intermediate for G102, and lowest for G104. Estimated by a linear-plateau model, gs and T of G100 started to decrease at significantly higher FTSW thresholds than did G102 and G104. An earlier closure of stomata and decrease of T in G100 would allow the plant to conserve water in the soil; however, owing to its putative larger leaf area and greater stomatal density on the adaxial leaf surface, G100 quickly depleted soil water and resulted in severe drought stress to the plants as exemplified by the significantly lowered gs, leaf area, and relative water content (RWC). In contrast, a smaller leaf area and a lower stomatal density on the adaxial leaf surface of G104 enabled the plants to slowly deplete soil water and maintain high gs, T, leaf area, and RWC 8 days after withholding irrigation. Coincided with these, the floral bud abortion rate in the D plants was significantly higher for G100 as compared with G102 and G104. It is concluded that in potted ornamentals, a low transpiration rate, hereby a slow rate of soil water depletion, is crucial for maintaining postharvest quality under drought stress.