Supplementary potassium and calcium improves salt tolerance in olive plants

10 Pags.- 3 Tabls.- 8 Figs.Soil salinization increase, aggravated by the foreseen low precipitation related to climate change, is a worldwide problem causing crop yield reductions, affecting population and environmental issues due to the salt-containing low-quality water. Enhancing the salt tolerance of plants, especially crops, is an interesting and effective solution to minimize salt-related crop problems. Toward this goal, we evaluated in this study the effect of potassium (K) and calcium (Ca) application on plant growth, nutrient uptake, water status and electrolyte and potassium leakage of two-year-old potted olive plants grown under saline conditions (100 and 200 mM NaCl). Results showed that all measured parameters were affected by salinity. However, the application of K and Ca enhanced the growth parameters, improved the water status and reduced the electrolyte and K leakage, the latter reflecting a positive effect in membrane integrity. The nutritional balance was moderately improved in salt-stressed plants treated with K and Ca. The significant reduction in sodium (Na) concentration in both leaves and roots, and the enhancement of K and Ca concentration in the different plant tissues indicated that the K and Ca supply raised the Na exclusion mechanism. The largest positive effect of K was observed with 40 mM KNO3 dose at both salinity levels. Furthermore, the beneficial effect of Ca was achieved with 40 and 10 mM CaCl2 in plants grown at 100 and 200 mM NaCl, respectively. Thus, for this relatively salt-tolerant and economically important crop, K and Ca are recommended to supply in order to mitigate the harmful effects of salinity and to develop saline agriculture in, for instance, coastal saline land.This work was supported by grants from Tunisian LPOI (LR16 IO 03-SERS-Tunisia) and International Plant Nutrition Institute (IPNI).Peer reviewe

Assessment of tolerance to NaCl salinity of five olive cultivars, based on growth characteristics and Na+ and Cl− exclusion mechanisms

10 Pags., 2 Tabls., 6 Figs.Changes caused by NaCl-induced salinity on several growth parameters and ions accumulation have been measured in five olive (Olea europaea L.) cultivars (‘Chemlali’, ‘Chetoui’, ‘Koroneiki’, ‘Arbequina I18’, and ‘Arbosana I43’) growing in a greenhouse in nutrient solution pot experiment. One-year-old plants were transplanted to sand–perlite (1:1) culture, and were irrigated with half-strength Hoagland nutrient solution containing NaCl at various levels (0.5, 50, 100 and 200 mM). Salinity induced significant decrease in growth parameters, but to a different extent in each cultivar. Leaf growth and total leaf area per plant were significantly affected by all salinity treatments in all studied cultivars, being ‘Arbequina I18’ the most sensitive cultivar. Leaf drop phenomenon was observed from 60 days after salt application at high salinity treatments, mainly in Arbequina I18. Contrary to leaf area, leaf thickness increased progressively during the experiment. ‘Chemlali’ developed thicker leaves at the two highest salinity treatments when compared to the other cultivars. Na+ and Cl− concentrations were higher in roots than in shoots and leaves in most of the cultivars investigated. The effectiveness of Na+ exclusion mechanism in the roots differed significantly among studied cultivars, working effectively in ‘Chemlali’ (by inhibiting translocation of Na+ to the aerial part) and being much less efficient in ‘Arbequina I18’. Furthermore, leaf abscission can be considered as an additional tolerance mechanism of olive cultivars allowing the elimination of leaves that had accumulated Na+ and Cl− ions. Tolerance to salinity stress was as follows: ‘Chemlali’ > ‘Chetoui’ > ‘Arbosana I43’ > ‘Koroneiki’ > ‘Arbequina I18’. This order of salt tolerance was indicated by lower reduction in plant growth parameters (shoot elongation, trunk diameter, total plant dry weight, internodes length, and total leaf area), the increase of leaf thickness, and by the effectiveness of the exclusion mechanism of Na+ and Cl− in the root system.This work was supported by grants from Olive tree Institute to Ajmi Larbi and Monji Msallem. Fermín Morales wishes to thank Gobierno de Aragón (A03 research group) for financial support.Peer reviewe

Genotypic differentiation in the stomatal response to salinity and contrasting photosynthetic and photoprotection responses in five olive (Olea europaea L.) cultivars

10 Pags., 2 Figs., 3 Tabls.Olive tree is moderately tolerant to salinity. Differences in salt tolerance among olive tree cultivars are documented. Salt-mediated decreases of stomatal conductance and photosynthesis are common in the studied cultivars, but other photosynthetic characteristics in response to increasing salinity are much less investigated. Greenhouse experiments were conducted to investigate the responses to increasing salinity up to 200mM NaCl of five olive tree cultivars: 'Chemlali', 'Chetoui', 'Arbequina I18', 'Arbosana I43' and 'Koroneiki', widely used in Tunisia. Techniques used include determinations of leaf concentrations of the toxic ions Na and Cl, photosynthetic pigment analyses, gas exchange and chlorophyll (Chl) fluorescence measurements. Relationships between thermal energy dissipation and changes in pigment composition were investigated. With 100mM NaCl water, the most readily available water in arid regions of Tunisia, 'Chemlali', 'Chetoui' and 'Arbosana' grew similarly to control plants, which is a valuable information for horticultural purposes. In all cultivars, leaf Na and Cl concentrations increased and net CO2 assimilation rates decreased as salt concentration increased. A negative correlation was observed between photosynthesis and leaf thickness. Data revealed genotypic differentiation in the stomatal response to salinity, decreasing in 'Koroneiki', 'Arbequina' and 'Arbosana' but remaining fairly constant in 'Chemlali' and 'Chetoui'. In those cultivars where the amount of energy thermally dissipated increased in response to salinity, it was well correlated with increases of (zeaxanthin+antheraxanthin)/(violaxanthin+antheraxanthin+zeaxanthin) ((Z+A)/(V+A+Z)) and lutein to Chl molar ratios. In summary, salinity caused marked reductions in photosynthetic rates well correlated with leaf Na and Cl accumulation. Photosynthesis limitation was partially attributed to stomata closure, except in the cultivars 'Chemlali' and 'Chetoui' in which stomatal conductances were unaltered. Possible decrease of CO2 mesophyll conductance mediated by increases of leaf thickness is discussed. Salinity increased Z+A- and/or lutein-mediated thermal energy dissipation of some of the olive tree cultivars investigated. © 2013 Elsevier B.V.This work was supported by grants from Olive Tree Institute (Tunisia) to Ajmi Larbi and Monji Msallem and AECID (grant AP/040397/11) to Ajmi Larbi and Anunciación Abadía (EEAD-CSIC). Ruth Sagardoy was supported by an I3P-CSIC predoctoral fellowship. Fermín Morales wishes to thank Gobierno de Aragón (A03 Research Group) for financial support.Peer reviewe