Interactions between Silicon and NaCl-Salinity in a Soilless Culture of Roses in Greenhouse

In an experiment with roses grown hydroponically, a low (0.3 mM) and a high (2 mM) level of silicon were combined with a low (0.8 mM) and a high (40 mM) NaCl concentration in the nutrient solution supplied to the crop. The aim of the experiment was to detect pos sible beneficial effects of silicon on plant growth, yield and flower quality and to test whether the deleterious effects of NaCl-salinity on roses could be mitigated by increasing the Si concentration in the root zone. Sili con was added to the nutrient solution in form of a wa ter-soluble potassium silicate compound. The electri cal conductivity (EC) in the nutrient solutions with low and high NaCl concentrations was 1.8 and 6.1 dS m_1, respectively, while the corresponding val ues in the drainage water, which indicated the salinity status in the root zone, were 2.3 and 8.2 dS nr1, re spectively. The increase of the NaCl concentration in the root zone restricted the above-ground vegetative weight of roses, the number of flowers per plant and the mean flower weight and stem length. The increased supply of Si significantly enhanced the vegetative growth of roses at both salinity levels, improved the overall ap pearance of the plants and resulted in a higher number of marketable flowers per plant at the low salinity lev el. However, silicon was unable to ameliorate the ad verse effects of NaCl-salinity on flower production and quality. The increased Si concentration in the root en vironment restricted the translocation of Na and CI to the young leaves of roses. However, net photosynthe sis, stomatal conductance and transpiration rate were not affected either by Si or by NaCl-salinity at the con centration levels tested in this study. This finding indi cates that the stimulation of the vegetative growth of roses by Si under conditions of high external salinity was not due to mitigation of toxic Na or Si effects on the photosynthetic apparatus.