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Biogas production was of increasing interest as it could not only produce biogas, but also treated manure that can be used as fertilizers. However, increasing level of NH 4 + in the effluent after anaerobic digestion needed to be considered. Using forage crops with high biomass production for bio-remediation of contaminated wastewater was an interesting alternative for wastewater treatment, but responses of the plants to such wastewater with nitrogen mainly in the form of NH 4 + associated with low O 2 availability were little known. Hence, growth, morphology, and minerals in plant tissues of hybrid Napier grass ( Pennisetum purpureum Schumach × Pennisetum americanum (L.) Leeke cv. Pakchong1) were determined under different combinations of NH 4 + (0.5, 1, 5, 10, 15 mM) and O 2 level (anoxia, hypoxia and normoxia). The plant growth decreased with O 2 depletion and strong effects were found in the plants grown in the anoxic condition, particularly, at the high NH 4 + concentrations (10, 15 mM). Similar results were found for number of roots, root length, and number of new shoots. Mineral concentrations in the plant tissues were affected by the O 2 depletion, especially N and P in the roots that decreased by 26% and 50%, respectively, at the absolute anoxic conditions as compared with the normoxic conditions. However, high Fe accumulation was found in the plants grown under the anoxic conditions. The hybrid Napier grass was able to tolerate the high NH 4 + up to 5 mM and could grow under the hypoxic condition with the total N slightly decreased. This species may have a potential for treating the wastewater discharged from the biogas production tank and at the same time could be used for animal feed or green manure after being harvested. [ABSTRACT FROM AUTHOR]

Growth, morphology, NH4 + uptake and mineral allocation in Salvinia cucullata Roxb. ex Bory grown with different amounts of NH4 + were investigated. Plants of uniform size were grown on full strength Smart and Barko medium with different NH4 + concentrations (0.5, 1, 5, 10 and 15mM) and incubated in a greenhouse for four weeks. Salvinia cucullata grew well in the medium with 0.5–1mM NH4 + with a relative growth rate of 0.11–0.12d−1 without exhibiting NH4 + toxicity symptoms. With an NH4 + concentration above 5mM, plant growth was suppressed and signs of NH4 + toxicity were observed. NH4 + toxicity symptoms were obvious in plants supplied with 10mM and 15mM NH4 +. These plants had low growth rates, short roots, low numbers of roots and showed chlorosis. Rotted roots and stems were also found in plants fed with 15mM NH4 +. This species had a high uptake rate even though the NH4 + concentrations increased, making it an ideal candidate for growth in eutrophic environments. The high NH4 + concentration had a negative effect on K uptake resulting in low K concentration in the plant tissue, but the plants increased N content in plant tissue. Thus, harvested plants can be used as soil fertilizer or for animal feed. Furthermore, maintaining plant biomass can improve the efficiency of water treatment. [Copyright &y& Elsevier]

The effects of high NH concentration on growth, morphology, NH uptake and nutrient allocation of Myriophyllum brasiliense were investigated in hydroponic culture. The plants were grown under greenhouse conditions for 4 weeks using four levels of NH concentration: 1, 5, 10 and 15 mM. M. brasiliense grew well with a relative growth rate of c.0.03 day at NH concentration up to 5 mM. At the higher NH concentrations the growth of the plants was stunted and the plants had short roots and few new buds, especially when grown in 15 mM NH where the submerged leaves were lost and there were rotten roots and submerged stems. To avoid NH toxicity, the plants may have a mechanism to prevent cytoplasmic NH accumulation in plant cells. The net uptake of NH significantly decreased and the total N significantly increased in the plants treated with 10 and 15 mM NH, respectively. The plant may employ NH assimilation and extrusion as a mechanism to compensate for the high NH concentrations. However, the plants may show nutrient deficiency symptoms, especially K deficiency symptoms, after they were exposed to NH concentration higher than 10 mM. The present study provides a basic ecophysiology of M. brasiliense that it can grow in NH enriched water up to concentrations as high as 5 mM. [ABSTRACT FROM AUTHOR]

Abstract: Many plants develop toxicity symptoms and have reduced growth rates when supplied with ammonium (NH4 +) as the only source of inorganic nitrogen. In the present study, the growth, morphology, NH4 + uptake kinetics and mineral concentrations in the tissues of the free-floating aquatic plant Salvinia natans (water fern) supplied exclusively with NH4 +–N at concentrations of 0.25–15mM were investigated. S. natans grew well, with relative growth rates of c. 0.25gg−1 d−1 at external NH4 + concentrations up to 5mM, but at higher levels growth was suppressed and the plants had small leaves and short roots with stunted growth. The high-affinity transport system (HATS) that mediate NH4 + uptake at dilute NH4 + levels was downregulated at high NH4 + concentrations with lower velocities of maximum uptake (V max) and higher half-saturation constants (K 1/2). High NH4 + levels also barely affected the concentrations of mineral cations and anions in the plant tissue. It is concluded that S. natans can be characterized as NH4 +-tolerant in line with a number of other species of wetland plants as growth was unaffected at NH4 + concentrations as high as 5mM and as symptoms of toxicity at higher concentrations were relatively mild. Depolarization of the plasma membrane to the equilibrium potential for NH4 + at high external concentrations may be a mechanism used by the plant to avoid excessive futile transmembrane cycling. S. natans is tolerant to the high NH4 + levels that prevail in domestic and agricultural wastewaters, and the inherent high growth rate and the ease of biomass harvesting make S. natans a primary candidate for use in constructed wetland systems for the treatment of various types of nitrogen-rich wastewaters. [Copyright &y& Elsevier]