effects of alkali stress and growing media on growth and physiological characteristics of gerbera plants

in order to determine the best growing media for gerbera jamesonii under alkaline conditions, a factorial experiment was conducted with two factors, namely: (i) growing medium, and (ii) concentrations of bicarbonate (nahco3) in nutrient solution. results showed that increasing the concentration of nahco3 from 0 to 40 mm in nutrient solution significantly decreased plant growth, maximal quantum yield of psii photochemistry (fv/fm), photosynthesis performance index (pi), glutamine synthetase (gs) activity, leaf relative water content (lrwc), chlorophylls (chl a, b and total chl) and carotenoids. under alkalinity stress, reduction in vegetative growth, fv/fm, pi, lrwc, gs activity and photosynthesis pigments content was the lowest in coconut fiber (cf) substrate compared to the other substrates. furthermore, plants grown in cf substrate had higher soluble sugars and proline content than those in other substrates. on the other hand, plants grown on perlite (p) substrate had the highest reduction in growth and physiological characteristic in alkaline conditions. the alleviation of alkalinity-induced growth inhibition of plants by cf substrate may be related to improvement of photosynthesis, enhancement of gs enzyme activity and osmotic regulation. it is concluded that the use of cf substrate could provide a useful tool to improve alkalinity tolerance of gerbera plants under nahco3 stress.