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 370μmol·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 370μmol·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 CO2 and at 400 – 500 μmol·m-2·s-1 PFD at 800 μmol·mol-1 CO2. For Kalanchoe similar results were obtained. Increasing the CO2 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 CO2 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 CO2 produced a similar result.
Highlights
The light condition in greenhouses varies considerably depending on the time of year and latitude
Supplementary lighting is a prerequisite for effective greenhouse production during wintertime; on cloudy days in the summer, supplementary lighting may be of benefit, for light-demanding crops such as cucumbers and cut roses [3]-[6]
The present study aimed to explore how pot plant species responded to photosynthetic active radiation (PAR) levels ranging from very low to very high
Summary
The light condition in greenhouses varies considerably depending on the time of year and latitude. At higher latitudes in summer, lower maximum irradiance levels during the day are compensated for by longer days (up to 24 h·day−1). Summer PAR levels depend mainly on weather conditions (cloud cover) and may vary considerably from day to day Supplementary lighting is a prerequisite for effective greenhouse production during wintertime; on cloudy days in the summer, supplementary lighting may be of benefit, for light-demanding crops such as cucumbers and cut roses [3]-[6]. Typically in Scandinavia, photon flux densities (PFD) of 100 to 150 μmol·m−2·s−1 are given to pot plants and of up to 200 to 300 μmol·m−2·s−1 to cut roses, tomatoes and cucumbers (16 to 20 h·day−1 lighting period).
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