title: Ammonium tolerance and toxicity of Actinoscirpus grossus--a candidate species for use in tropical constructed wetland systems.
abstract: Actinoscirpus grossus, a native species in tropical wetlands of South-East Asia, North Australia and the Pacific islands, has been reported to perform well in experimental scale constructed wetland (CW) systems. However, little is known about how high NH4(+) concentrations prevailing in wastewater affect growth and performance of this species. We examined growth, morphological and physiological responses of A. grossus to NH4(+) concentrations of 0.5, 2.5, 5, 10 and 15mM under hydroponic growth conditions. The relative growth rates (RGR) of the plants were highest at 2.5mM NH4(+) but significantly reduced at 10 and 15mM NH4(+). The roots of the plants were stunted and produced subepidermal lignified-cell layers at exposure to 10 and 15mM NH4(+). The photosynthetic rates did not differ between treatments (average An=21.3±0.4µmolCO2m(-2)s(-1)) but the photosynthetic nitrogen and carbon use efficiency (PNUE and PCUE) were significantly depressed at 10 and 15mM NH4(+) treatments. The concentration of NH4(+) in the roots, but not in the leaves, reflected the NH4(+) concentration in the growth medium suggesting that the species is unable to regulate the NH4(+) uptake. The high root respiration rates in concert with high tissue NH4(+) and declined C/N ratio at 10 and 15mM NH4(+) suggest that the NH4(+) assimilation occurs primarily in the roots and the plant has inadequate C-skeletons for NH4(+) assimilation and exudation at high NH4(+) concentration in the external solution. The concentrations of mineral cations were generally reduced and the root membrane permeability increased at high external NH4(+) concentrations. Our study shows that A. grossus tolerates NH4(+) concentrations up to 5mM which is characteristic of most types of wastewater. Hence, A. grossus is a good native candidate species for use in CW systems in tropical and subtropical climates in South-East Asia, North Australia and the Pacific islands.
authors.affiliation: Faculty of Science and Technology, Aarhus University, Ole Worms Allé 1, 8000 Aarhus C, Denmark. Electronic address: piwpuan@hotmail.com.
authors.forename: Narumol
authors.initials: N
authors.lastname: Piwpuan
authors.affiliation: Department of Biology, Faculty of Science, Chiang Mai University, Meuang, Chiang Mai 50202, Thailand.
authors.forename: Arunothai
authors.initials: A
authors.lastname: Jampeetong
authors.affiliation: Faculty of Science and Technology, Aarhus University, Ole Worms Allé 1, 8000 Aarhus C, Denmark.
authors.forename: Hans
authors.initials: H
authors.lastname: Brix
mesh_terms: D064751:Ammonium Compounds / Q000633:toxicity*; D001315:Australia; D018533:Biomass; D029785:Cyperaceae / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D018527:Hydroponics; D009584:Nitrogen / Q000378:metabolism; D010758:Phosphorus / Q000378:metabolism; D010788:Photosynthesis; D010860:Pigments, Biological / Q000378:metabolism; D019441:Plant Epidermis / Q000187:drug effects; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism; D011897:Random Allocation; D014329:Tropical Climate; D018505:Waste Management; D053833:Wetlands
chemical_list: D064751:Ammonium Compounds; D010860:Pigments, Biological; D010758:Phosphorus; D009584:Nitrogen
keywords: Emergent macrophyte; Giant bulrush; PNUE; Scirpus grossus; Wastewater treatment