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Many plant species can adapt to flooding and hypoxia by forming a root system with an altered architecture: thicker, shorter and shallower adventitious roots, than under aerated conditions. The internal gas transport is often improved by increased root porosity and aerenchyma, which is tissue with large intercellular spaces. The raised root aeration allows better supply of oxygen to plant tissues and diffusion of oxygen into the rhizosphere (Radial Oxygen Loss, ROL). This phenomenon creates narrow, but well aerated zones in the hypoxic soil, where phytotoxins are oxidised and methanotrophic as well as nitrifying bacteria can live. The aim of the study was to determine the change of root archi-tecture, porosity and ROL from roots of Plantago lanceolata plants originating from The Middle Vistula River Gorge. Selected plant species were subjected to transient flooding during 7 days of culti-vation on aerated and stagnant oxygen-deficient hydroponic medium. We observed the formation of shorter hypoxic, adventitious roots (56-69 mm) than control roots (112-196 mm) with high porosity (stagnant 15-21 %, control 8.5-9.4%), and the diameter of aerated zone (halo) increased from control values of 0-1.5 mm to 2-2.5 mm under hypoxic conditions.
The environmental pollution resulting from natural resources acquisition is one of the most severe problems nowadays. New environmental friendly and economically attractive techniques are proposed, using the ability of microorganisms (bioremediation) or plants (phytoremediation) for detoxification of their substrate. Depending on the type of pollutant and the mechanism of its immobilisation (accumulation or decomposition), several techniques are proposed. The specialised plant spe-cies are called hyperaccumulators, e.g. Brassica juncia, Helianthus annuus, Nicotiana tabacum or genetically modified Arabidopsis thaliana. Azolla caroliniana Willd. (Azollaceae) is an aquatic fern occurring in temperate and tropical climates. Recently, some natural stands of it were found in western Poland. The fern lives in symbiosis with cyanobacterium Anabaena azollae which is capable of fixing atmospheric nitrogen. Besides numerous application of Azolla in agriculture, e.g. as green manure, it was found that this plant possess a huge ability for phytoremediation. Our studies showed its ability for removal and accumulation of Hg, Cd, Pb, Cr, As, Ag, Pt and Au from waters (up to 100% of applied doses). These promising results open a new application of Azolla spp. for the purification of water polluted by heavy metals, for example as an additional step of wastewater purification.
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