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How chrysanthemum (Chrysanthemum × grandiflorum) ‘Palisade White’ deals with long-term salt stress
AbstractSalinity is a serious problem in the cultivation of ornamental plants. Chrysanthemum (Chrysanthemum × grandiflorum) ‘Palisade White’ was evaluated in order to examine its responses to long-term salt stress. Plants were grown in substrate supplemented with NaCl doses (g dm−3 of substrate) 0, 0.44, 0.96, 1.47, 1.98, 2.48 and 2.99. The initial electrical conductivity (EC) of the substrates was 0.3, 0.9, 1.4, 1.9, 2.6, 3.1 and 3.9 dS m−1, respectively. Plant growth, relative water content (RWC), Na, Cl, K, N and P concentrations, membrane injury (MI), chlorophyll and proline levels, as well as gas exchange parameters in leaves of chrysanthemum were determined. A dose-dependent significant reduction of growth and minor decrease of leaf RWC were observed. Foliar Na and Cl concentrations increased with the highest NaCl dose up to 6-fold. However, the concentration of K increased by about 14 %, N by about 5 % but P decreased by about 23 %. Membrane injury was rather low (11 %) even at the highest NaCl dose. Statistically significant decreases of stomatal conductance (20 %), transpiration rate (32 %) and photosynthesis (25 %) were already observed at the lowest NaCl dose and about 40 % decrease of all these parameters with the highest dose. A significant reduction in the intercellular CO2 concentration occurred at the lower NaCl doses and no changes with the highest dose. These results show that in plants grown with the highest NaCl dose, non-stomatal limitation of photosynthesis may occur. According to Maas and Hoffman tolerance assessment (1977) chrysanthemum ‘Palisade White’ may be considered as moderately sensitive to salt stress in terms of growth inhibition. However, it is able to cope with long-term salt stress without any signs of damage, such as chlorophyll depletion, leaf browning or necrotic spots probably due to maintenance of K homeostasis and proline accumulation, which alleviate the toxic effect of chloride.
Does Potassium Modify the Response of Zinnia (Zinnia elegans Jacq.) to Long-Term Salinity?
Salinity is one of the major abiotic stress factors hindering crop production, including ornamental flowering plants. The present study examined the response to salt stress of Zinnia elegans ‘Lilliput’ supplemented with basic (150 mg·dm−3) and enhanced (300 mg·dm−3) potassium doses. Stress was imposed by adding 0.96 and 1.98 g of NaCl per dm−3 of the substrate. The substrate’s electrical conductivity was 1.1 and 2.3 dS·m−1 for lower potassium levels and 1.2 and 2.4 dS·m−1 for higher potassium levels. Salt stress caused a significant and dose-dependent reduction in leaf RWC, increased foliar Na and Cl concentrations, and reduced K. About 15% and 25% of cell membrane injury at lower and higher NaCl doses, respectively, were accompanied by only slight chlorophyll reduction. Salt stress-induced proline increase was accompanied by increased P5CS activity and decreased PDH activity. More than a 25% reduction in most growth parameters at EC 1.1–1.2 dS·m−1 but only a slight decrease in chlorophyll and a 25% reduction in the decorative value (number of flowers produced, flower diameter) only at EC 2.3–2.4 dS·m−1 were found. Salt stress-induced leaf area reduction was accompanied by increased cell wall lignification. An enhanced potassium dose caused a reduction in leaf Na and Cl concentrations and a slight increase in K. It was also effective in membrane injury reduction and proline accumulation. Increasing the dose of potassium did not improve growth and flowering parameters but affected the lignification of the leaf cell walls, which may have resulted in growth retardation. Zinnia elegans ‘Lilliput’ may be considered sensitive to long-term salt stress.
The Effect of NaCl Stress on the Response of Lettuce (Lactuca sativa L.)
In recent decades, increasing human pressure has caused the gradual deterioration of the physical and chemical properties of water and soil. Salinity is an important factor influencing the quality of water. The aim of this comprehensive research was to determine the effect of increasing concentrations of sodium chloride, which is a salinity inducer, on the yield, photosynthesis efficiency (expressed with chlorophyll fluorescence measurement) and content of selected nutrients in the leaves of hydroponically grown lettuce (Lactuca sativa L.). Experiments were conducted at the following concentrations of NaCl: 0 (control treatment), 10, 20, 40, and 60 mmol L−1. Studies were conducted in two independent seasons: spring and autumn. The plants exposed to NaCl stress modified their chemical composition by lowering the uptake of (for 60 mmol L−1 NaCl in relation to control): N (−11%), K (−35.7%), and Mg (−24.5%), while increasing the sodium content (+2400%). The Na:K ratio was significantly narrowed (from 76:1 to 2.6:1). The increase in the Cl level in the lettuce leaves may also have caused a decrease in the content of nitrates. As a result of disturbed ionic balance, the RWC was significantly reduced (−6.2%). As a result of these changes, the yield of the biomass of the aerial parts decreased (more than two-fold for the highest NaCl concentration in relation to control) whereas the dry matter content increased (+32%). The measurement of fluorescence showed significant changes at the PSII level. Salinity modified the energy flow rate (F0, FM, FV, FV/FM) as well as the specific energy flows through the reaction centre (ABS/RC, TR0/RC, ET0/RC, DI0/RC). The PSII functioning index, calculated on the basis of energy absorption (PIAbs), also changed. The salinity induced with NaCl significantly worsened the physiological reactions of the plants in the PSII, changed the ionic balance, which resulted in a significantly lower yield of the plants. Due to increasing water quality problems, it will be necessary to use, in agriculture on a much larger scale than before, saline water treatment systems (e.g., highly effective nanofiltration and/or reverse osmosis).