Articles
EFFECT OF VARIOUS WATER VAPOUR PRESSURE DEFICIT GRADIENTS AND NITROGEN LEVELS ON MORPHOGENESIS OF EUPHORBIA PULCHERRIMA ‘FREEDOM‘
At a higher night temperature than day temperature, (negative DIF) we know today that many plant species respond with a decreased stem elongation.
In order to study how important water vapour gradients are in this connection, Euphorbia pulcherrima ‘Freedom’ was grown at two different water vapour pressure deficits, under flourescent lamps, in four climate chambers of the biotron at Alnarp.
The temperature was kept at 20°C (±0,1 °C).
A high water vapour pressure deficit will increase the transpiration from the plant and water and nutrient uptake will therefore also be increased.
The nutrients were applied as a complete nutrient solution with additions of Ca(NO3)2 at four different levels.
The cyathia of the unfertilized plants developed very slowly or did not flower at all.
Of the fertilized plants those which had been grown at a WVPD of 0.94 kPa at day (D) and 0.24 kPa at night (N) had the most rapid development.
However, those which had been grown at a WVPD of D 0.24 kPa/N 0.94 kPa, flowered several days later.
Plant height and the length of the main shoot were only affected slightly by the different WVPD treatments.
The elongation was smallest at a WVPD of 0.94 kPa day and night.
These plants also had the biggest bract ("star") diameter, the highest number of bracts per plant and the most intense leaf colour.
Even the unfertilized plants were darker green in this treatment.
Constant low WVPD day and night and a high WVPD during night both resulted in lighter green leaves and smaller bracts which resulted in a smaller "star" diameter even for the plants which received the highest nutrient supply.