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In constructed wetlands (CWs) with forced aeration and vertical flow, plants can suffer from iron (Fe) deficiency due to Fe immobilization in the gravel substrate as a consequence of the oxic condition. The common reed ( Phragmites australis ) is the most commonly used plant species in CWs and frequently displays Fe-deficiency symptoms particularly in new-established systems. The aim of this study was therefore to study the Fe-nutrition of P. australis in order to gain knowledge on how Fe-deficiency in P. australis can be alleviated. For this purpose, we grew two genetically distinct phylogeographic groups of P. australis hydroponically with seven different Fe concentrations (0, 0.1, 0.2, 0.5, 1.0, 5.0 and 20.0 mg Fe-EDDHA ([iron (3+) ethylenediamine di (o-hydroxyphenylacetic) acid]) L −1 ) in a phytotron. Both groups responded strongly to the increasing Fe supply. The belowground biomass allocation ratio, light-saturated photosynthesis rates, chlorophyll content and leaf Fe tissue concentration all significantly increased with increasing Fe availability. Phragmites australis in the 0 mg Fe-EDDHA L −1 treatment suffered strongly from Fe deficiency, and plants in the high 20.0 mg Fe-EDDHA L −1 treatment also had reduced growth and Fe toxicity symptoms. The ‘critical deficiency concentration’ of Fe in leaves of juvenile P. australis was 40–50 mg kg −1 DM, and the ‘critical toxicity concentration’ of Fe in leaves of juvenile P. australis were approximately 150 mg kg −1 DM. Overall the two genetically distinct P. australis groups differed in their ecophysiological traits, and the two groups also responded differently to the different Fe-supply rates which may be the result of adaptations obtained in their native growth habitats. We suggest that the Fe-deficiency in CW systems with unsaturated vertical flow and/or forced aeration can be alleviated by application of a foliar spray containing chelated iron. However, the application rate and frequency should be further studied. [ABSTRACT FROM AUTHOR]

Supplemental calcium (Ca2+) is used in hydroponic studies on salinity to lessen the potential for Ca2+ deficiency. However, the Ca2+ concentration and the sodium (Na+): Ca2+ ratio used vary considerably. The implications of using a wide range of Na+: Ca2+ ratios for studies of salinity tolerance in wheat are not known. Also, despite the risk of development of Ca2+ deficiency under salinity stress, there are few reliable reports on the critical level of Ca2+ which can be used to diagnose Ca2+ deficiency in wheat. Two experiments were conducted to examine Ca2+ requirements of wheat under saline and non-saline conditions and to derive a critical level for Ca2+. Four bread wheat genotypes ( Triticum aestivum L.) and a durum wheat genotype [ Triticum turgidum subsp . durum) (Desf.) Husn.] with known differences in salinity tolerance were grown at 100 mM NaCl for four weeks with varying levels of external Ca2+ which resulted in Na+:Ca2+ ratios of 30, 20, 15, 5 and 2. The critical Ca2+ concentration was defined in a second experiment by growing the same wheat genotypes at seven levels of Ca2+ (0.05, 0.1, 0.2, 0.5, 1, 2 and 10 mM) under non-saline conditions. When grown at 100 mM NaCl salinity tolerance was greatest when the Na+:Ca2+ ratio ranged from 5 to 15. Growing plants at lower or higher Na+:Ca2+ ratios induced nutrient imbalances and additional osmotic stress which reduced the growth of plants. Transient Ca2+ deficiency occurred at high Na+:Ca2+ ratios and low Mg2+ occurred at the lowest Na+:Ca2+ ratio. Adding NaCl raised the tissue Na+ concentration and reduced the Ca2+ concentration and the most appropriate Na+:Ca2+ ratio in the solution was that which resulted in tissue Ca2+ concentrations similar to those of non-salinised plants. The critical level of Ca2+ in the youngest fully emerged leaf blades was 15–23 mmol kg-1 DW (600–900 mg kg-1 DW). [ABSTRACT FROM AUTHOR]