The Effect of Wide-Range Photosynthetic Active Radiations on Photosynthesis, Growth and Flowering of <i>Rosa sp.</i> and <i>Kalanchoe blossfeldiana</i>

Abstract

Miniature roses (Rosa sp.) and Kalanchoe blossfeldiana were grown at photon flux densities (PFD) ranging from 60 to 670 μmol·m -2 ·s -1 (associated with a temperature gradient from 20.0°C to 24.0°C [TEMP1]) and from 50 to 370 μmol·m -2 -s -1 (associated with a temperature gradient from 22.5°C to 26.5°C [TEMP2]). The experiment was conducted in a greenhouse compartment at latitude 59° north in mid-winter. The daily photosynthetic active radiations (PAR) ranged from 4.3 to 48.2 and 3.6 to 26.6 mol·m -2 ·day -1 in the TEMP1 and TEMP2 treatments, respectively. Time until flowering in miniature roses decreased from about 50 to 35 days in the TEMP1 treatment and from 50 to 25 days in the TEMP2 treatment, when the PFD increased from 50 to 370 μmol·m -2 ·s -1 . In Kalanchoe time until flowering was decreased to the same extent (about 15 days) in both temperature treatments when PFD increased from 50 to 370 μmol·m -2 ·s -1 . The number of flowers and the plant dry weight in miniature roses increased up to 300 – 400 μmol·m -2 ·s -1 PFD (21.6 - 28.8 mol·m -2 day -1 PAR), while flower stem fresh weight and plant dry weight in Kalanchoe increased up to 200 – 300 μmol·m -2 ·s -1 at TEMP1. Measurements of the diurnal carbon dioxide exchange rates (CER) in daylight in small plant stands of roses in summertime showed that CER was saturated at about 300 μmol·m -2 ·s -1 PFD at 370 μmol·mol -1 CO 2 and at 400 – 500 μmol·m -2 ·s -1 PFD at 800 μmol·mol -1 CO 2 . For Kalanchoe similar results were obtained. Increasing the CO 2 concentration from 370 to 800 μmol·mol -1 increased the CER in roses (48%) as well in Kalanchoe (69%). It was concluded that 15 to 20 mol·m -2 ·day -1 combined with about 24°C air temperature and high CO 2 concentration will give a very good growth with lot of flowers within a short production time in miniature roses. For Kalanchoe 10 to 15 mol·m -2 ·day -1 combined with about 20°C and high CO 2 produced a similar result.