Effects of Alkali Stress and Growing Media on Growt h and Physiological Characteristics of Gerbera Plants

Abstract

In order to determine the best growing media for Gerbera jamesonii under alkaline conditions, a factorial experiment was conducted wi th two factors, namely: (i) Growing medium, and (ii) Concentrations of bicarbonate (NaH CO 3 ) in nutrient solution. Results showed that increasing the concentration of NaHCO 3 from 0 to 40 mM in nutrient solution significantly decreased plant growth, maxi mal quantum yield of PSII photochemistry (F v /F m ), photosynthesis Performance Index (PI), Glutamine Synthetase (GS) activity, Leaf Relative Water Content (LRWC), C hlorophylls (Chl a, b and total Chl) and carotenoids. Under alkalinity stress, redu ction in vegetative growth, F v /F m , PI , LRWC , GS activity and photosynthesis pigments content w as the lowest in Coconut Fiber (CF) substrate compared to the other substrates. Fu rthermore, plants grown in CF substrate had higher soluble sugars and proline con tent than those in other substrates. On the other hand, plants grown on Perlite (P) substra te had the highest reduction in growth and physiological characteristic in alkaline condit ions. The alleviation of alkalinity- induced growth inhibition of plants by CF substrate may be related to improvement of photosynthesis, enhancement of GS enzyme activity a nd osmotic regulation. It is concluded that the use of CF substrate could provid e a useful tool to improve alkalinity tolerance of gerbera plants under NaHCO 3 stress. Keywords: Alkalinity, Glutamine synthetase activity, Growing media, Osmotic adjustment, Photosynthetic pigments.