| heal.abstract |
The effects of a progressively increase of Na and Cl concentrations in the root zone of pepper grown in a fully closed hydroponic system on plant growth, photosynthesis, nutrient uptake, and yield were investigated in an 8-month greenhouse experiment. Four different salinity treatments were tested in 12 hydroponic units, which corresponded to the use of irrigation water with four different NaCl concentrations, particularly 0.8, 4, 8 and 12 mM. Thus, each salinity level was replicated three times. The irrigation water with the four different NaCl concentrations was used to prepare fresh nutrient solution, which was supplied independently in each experimental unit by means of drip irrigation systems to compensate for plant uptake. To establish the different NaCl treatments, irrigation water containing 0.8 mM NaCl was used, which was enriched with additional NaCl at quantities resulting in the above referenced final NaCl concentrations. Each experimental treatment was replicated three times. The electrical conductivity (EC) in the recycled drainage solution was increasing for several months but finally it tended to stabilize at maximal levels, which were different in each treatment, depending on the NaCl concentrations in the irrigation water. The increase of EC was due mainly to accumulation of Na and Cl, but Ca, Mg, and K tended also to accumulate in the drainage solution. The accumulation of Na and Cl in the root zone reduced K + and Ca +2 concentrations in all tissues and Mg +2 in fruits, roots and stems but enhanced the Mg level in new and old leaves. The increased salt concentration in the drainage solution significantly reduced the vegetative growth of sweet pepper, as reflected by measurements of fresh and dry weight of the aboveground plant parts, as well as the fruit production. The photosynthetic ability and the leaf transpiration rates were significantly decreased by salinity due to both accumulation of Na + and Cl - in the photosynthetically active leaves and reduction of stomatal conductance. |
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