Seasonal and diurnal photosynthetic responses of two gerbera cultivars to different substrates and heating systems

The simultaneous, long-term effects of three substrates (zeolite, perlite a nd their 1.1 mixture) and of two heating systems (lower and upper) upon the diurnal changes in photosynthesis of two gerbera cultivars (Cyprus and Hea rt Breaker) were investigated at different times of year. 'Cyprus' revealed higher net CO2 assimilation rate and stomatal conductance than 'Heart Brea ker', while transpiration rate was almost the same. Based on both stomatal conductance and transpiration rate, the zeolite-perlite mixture substrate e xerted a more beneficial effect on the soil-plant water system. No change i n chlorophyll levels, either time-wise or between gerbera cultivars, was ob served in response to different substrates and heating systems. Diurnal net CO2 assimilation rate, followed only for 'Cyprus', was reduced significant ly from morning to late afternoon, possibly as a result of stomatal conduct ance reduction. The practical outcome with respect to the combined effect o f different substrates, heating systems and cultivars was that 'Cyprus' gro wn on the mixture medium and subjected to an upper heating system (i.e, wit h heating pipes installed at the culture bag level) exhibited the best phys iological responses. (C) 2001 Elsevier Science B.V. All rights reserved.