Calcium distribution in cut roses as related to transpiration

Abstract

SummaryIn contrast to many other horticultural crops, cut roses show higher concentrations of Ca in the leaves at the top of the flower stem than in those at the bottom. This study aimed to investigate the distribution of Ca along the stem of roses, to assess whether Ca accumulation in roses might be governed by factors other than transpiration. Ca concentrations in the leaves decreased from bottom to top of the stem. The effects of air vapour pressure deficit (VPD), removal of leaves and/or bent down stems on Ca concentrations in the leaves and petals were studied in greenhouse experiments. A lowerVPD resulted in an 11% increase in the number of flowering stems, which was offset by a lower average stem weight. Although transpiration was on average 25% lower in the low-VPD treatment over the whole experimental period, it was not (winter period) or only slightly (summer) related to lower Ca concentrations in the petals, stems or leaves. This limits the possibility for Ca enhancement by influencing transpiration. Removal of part of the leaves and/ or bent-down stems increased Caconcentrations in the remaining leaves and petals, primarily through decreased dryweight accumulation. Leaf diffusion resistance decreased along the stem from bottom to top leaves. In postharvest transpiration studies, stomatal densities and transpiration rates per unit leaf area were both higher in top than in bottom leaves. The findings indicate that local Ca concentrations in the rose organs can be related to their respective transpiration rates.