Nitrogen Fertilization of Plants Irrigated with Desalinated Water: A Study of Interactions of Nitrogen with Chloride

The overall aim of this research was to optimize nitrogen (N) fertilization of plants under desalinated water and a wide range of chloride concentrations for high yield while minimizing downward leaching of nitrate and chloride. The response of two crops, lettuce and potato, to N concentration (CN) in the irrigating solution using desalinated and wide range of Cl concentrations (CCL) was evaluated. The yields of both crops increased with N up to optimal CN of the irrigating solution and decreased as CCL increased. Optimal CN in both crops was higher in the desalinated water than high CCL treatments. N uptake by plants increased with CN in the irrigating solution and the highest uptake was at low CCL. As expected, N fertilization suppressed Cl accumulation in plant tissues. Drainage of N and Cl increased with increase in CCL in the irrigating solution and N fertilization above optimal CN resulted in steep rise in downward N leaching. The overall conclusion is that as water quality is improved through desalination, higher N supply is required for high yields with less groundwater pollution by downward leaching of N and Cl.

Increased water salinity applied to tomato plants accelerates the development of the leaf miner Tuta absoluta through bottom-up effects

Variation in resource inputs to plants may trigger bottom-up effects on herbivorous insects. We examined the effects of water input: optimal water vs. limited water; water salinity: with vs. without addition of 100 mM NaCl; and their interactions on tomato plants (Solanum lycopersicum), and consequently, the bottom-up effects on the tomato leaf miner, Tuta absoluta (Meytick) (Lepidoptera: Gelechiidae). Plant growth was significantly impeded by limited water input and NaCl addition. In terms of leaf chemical defense, the production of tomatidine significantly increased with limited water and NaCl addition, and a similar but non-significant trend was observed for the other glycoalkaloids. Tuta absoluta survival did not vary with the water and salinity treatments, but the treatment “optimal water-high salinity” increased the development rate without lowering pupal mass. Our results suggest that caution should be used in the IPM program against T. absoluta when irrigating tomato crops with saline water.

Metabolite profile of the tomato dwarf cultivar Micro-Tom and comparative response to saline and nutritional stresses with regard to a commercial cultivar

BACKGROUND

The dwarf tomato variety Micro-Tom has been used as a plant model for studies of plant development. However, its response to environmental and agricultural factors has not been well studied. This work studies the phytochemical content of Micro-Tom tomato and its comparative response to saline and nutritional (N, K and Ca) stresses with regard to a commercial variety.

RESULTS

The chromatographic profiles of Micro-Tom were similar to those of the commercial variety and the only differences appear to be the concentration of the components. In Micro-Tom, the concentrations of sugars and organic acids increased by salinity in a lesser extent than in Optima. Moreover, contrary to that observed in the commercial variety, phenolic compounds and vitamin C did not increase by salinity in the dwarf variety. However, both varieties increased similarly the concentrations of carotenoids under saline conditions. Finally, fruit yield and most primary and secondary metabolite concentrations in Micro-Tom were not affected by N, K or Ca limitation.

CONCLUSIONS

The mutations leading to the dwarf phenotype did not greatly alter the metabolite profiles but studies using Micro-Tom as a plant model should consider the lower capacity for sugars and organic acids under saline conditions and the greater tolerance to nutrient limitation of the dwarf variety.

Effects of acute ozone stress on reproductive traits of tomato, fruit yield and fruit composition

BACKGROUND

Tomato is sensitive to ozone. Fruit growth and composition are altered under ozone stress by modification of reproductive development. Fifty-one-day-old plants were exposed to three concentrations of ozone (200, 350 and 500 µg m(-3)) for 4 h.

RESULTS

Ozone reduced well-developed fruit number and fruit size, but it did not significantly affect flowering rate and fruit setting rate. The effect of ozone depends on organ developmental stage at the time of ozone application, as flowers and young fruits at the time of ozone exposure were more affected. Contents of total soluble sugars (total SS), total organic acids (total OA) and ascorbic acid (AsA) increased in fruits harvested from ozone-treated plants. Tomato fruit composition was altered under ozone stress, leading to a lower sugar:acid ratio. These changes were mostly due to increased contents of malic acid, ascorbate and glucose despite a decrease in sucrose.

CONCLUSION

Acute ozone exposure up to 500 µg m(-3) greatly influences tomato fruit quality. As final fruit yield was not significantly reduced, it highlighted that there may be compensatory mechanisms present in the reproductive structures of tomato. Further research would be necessary to determine how reproductive traits are affected by repeated ozone exposure or longer-term exposure.

The role of nitrogen availability for the salt-tolerance of two different varieties of durum wheat

Salt stress tolerance of durum wheat was assessed in control and 200 and 300 mM NaCl-exposed seed of two cultivars (BidiAP4 and Azizi). These salt treatments were accompanied by different levels of nitrate (Ca(NO3)2) added to the media (0.1, 3, 10 mM). The data showed that NaCl stress increased Na(+) and Cl(-) contents and lowered K(+) and NO3 (-) levels in seeds of BidiAP4 cultivar. In Azizi seeds exposed to NaCl, Na(+) and K(+) were highly accumulated while low levels of NO3 (-) and Cl(-) were detected. Those findings highlight the difference in the salt stress tolerance of these two durum wheat cultivars also depending on nitrogen (N) availability, Azizi cultivar being less sensitive to NaCl treatment than BidiAP4. These data also suggested a relationship between salt tolerance capacity and enhancement or maintenance of nitrogen and carbon metabolisms enzyme activity.

NaCl stress effects on enzymes involved in nitrogen assimilation pathway in tomato "Lycopersicon esculentum" seedlings

Tomato plants (Lycopersicon esculentum Mill, cv. Chibli F1) grown for 10 days on control medium were exposed to differing concentrations of NaCl (0, 25, 50, and 100mM). Increasing salinity led to a decrease of dry weight (DW) production and protein contents in the leaves and roots. Conversely, the root to shoot (R/S) DW ratio was increased by salinity. Na(+) and Cl(-) accumulation were correlated with a decline of K(+) and NO(3)(-) in the leaves and roots. Under salinity, the activities of nitrate reductase (NR, EC 1.6.6.1) and glutamine synthetase (GS, EC 6.3.1.2) were repressed in the leaves, while they were enhanced in the roots. Nitrite reductase (NiR, EC 1.7.7.1) activity was decreased in both the leaves and roots. Deaminating activity of glutamate dehydrogenase (GDH, EC 1.4.1.2) was inhibited, whereas the aminating function was significantly stimulated by salinity in the leaves and roots. At a high salt concentration, the nicotinamide adenine dinucleotide reduced (NADH)-GDH activity was stimulated concomitantly with the increasing NH(4)(+) contents and proteolysis activity in the leaves and roots. With respect to salt stress, the distinct sensitivity of the enzymes involved in nitrogen assimilation is discussed.

Salinity-induced tissue-specific diurnal changes in nitrogen assimilatory enzymes in tomato seedlings grown under high or low nitrate medium

We studied the salt stress (100 mM NaCl) effects on the diurnal changes in N metabolism enzymes in tomato seedlings (Lycopersicon esculentum Mill. cv. Chibli F1) that were grown under high nitrogen (HN, 5 mM NO(3)(-)) or low nitrogen (LN, 0.1 mM NO(3)(-)). NaCl stress led to a decrease in plant DW production and leaf surface to higher extent in HN than in LN plants. Total leaf chlorophyll (Chl) content was decreased by salinity in HN plants, but unchanged in LN plants. Soluble protein content was decreased by salt in the leaves from HN and LN plants, but increased in the stems-petioles from LN plants. Nitrate reductase (NR, EC 1.6.1.6) showed an activity peak during first part of the light period, but no diurnal changes were observed for the nitrite reductase (NiR, EC 1.7.7.1) activity. Glutamine synthetase (GS, EC 6.3.1.2) and glutamate synthase (Fd-GOGAT, EC 1.4.7.1) activities increased in HN plant leaves during the second part of the light period, probably when enough ammonium is produced by nitrate reduction. NR and NiR activities in the leaves were more decreased by NaCl in LN than in HN plants, whereas the opposite response was obtained for the GS activity. Fd-GOGAT activity was inhibited by NaCl in HN plant leaves, while salinity did not shift the peak of the NR and Fd-GOGAT activities during a diurnal cycle. The induction by NaCl stress occurred for the NR and GS activities in the roots of both HN and LN plants. Glutamate dehydrogenase (GDH, EC 1.4.1.2) activity shifted from the deaminating activity to the aminating activity in all tissues of HN plants. In LN plants, both aminating and deaminating activities were increased by salinity in the leaves and roots. The differences in the sensitivity to NaCl between HN and LN plants are discussed in relation to the N metabolism status brought on by salt stress.