Water balance of cut and intact «Sonia» rose plants

Abstract

Summary For validly interpreting certain aspects of cut-flower physiology it is a prerequisite to compare the behaviour of cut flowers with that of intact ones, side by side, under the same environmental conditions. Fresh weight, water loss and water uptake of hydroponically grown, single-stem roses with or without a root system were followed throughout one blooming period, by twice-daily weighings. In the intact plants shoot plus flower weight could be estimated reliably with a water-displacement technique eliminating root weight. Cut roses standing in water very soon started to develop a characteristic pattern of weight fluctuations, in accordance with the light-dark alternation, losing ca. 10% weight in the light and regaining it in darkness. The pattern persisted after petal shedding, but on a roughly 50% reduced scale; this means that both petals and foliage contributed to the fluctuations observed. In the intact roses actual weight losses only occurred shortly before petal shedding, in the light, and did not persist thereafter; thus here it was only the senescing petals that lost some of their water-retaining capacity. Total daily water loss and uptake of the cut roses were identical to those of the intact ones in the first 24 h, but rapidly declined subsequently, levelling off to some 10%. In the same lapse of time overall water loss and uptake of the intact roses slowly declined as well, by some 30%. In the dark periods water uptake of the cut roses did not decline, as it did in the light, but remained constant and equal to that of the intact roses for most of the time. This is taken to mean that the phenomenon of rapidly declining overall water uptake of cut roses is not caused by a massive, solid plugging of the xylem vessels, as almost generally inferred in the literature. An alternative hypothesis is put forward.