Response of Salvinia cucullata to high NH 4 þ concentrations at laboratory scales Arunothai Jampeetong a,n , Hans Brix b , Suwasa Kantawanichkul c a Department of Biology, Faculty of Science, Chiang Mai University, Meuang, Chiang Mai 50202, Thailand b Department of Bioscience, Plant Biology, Aarhus University, Ole Worms Alle´ 1, 8000 Aarhus C, Denmark c Department of Environmental Engineering, Faculty of Engineering, Chiang Mai University, Chiang Mai 50200, Thailand article info Article history: Received 8 July 2011 Received in revised form 2 December 2011 Accepted 3 December 2011 Available online 21 December 2011 Keywords: Aquatic fern Futile cycling NH 4 þ toxicity Salvinia cucullata abstract Growth, morphology, NH 4 þ uptake and mineral allocation in Salvinia cucullata Roxb. ex Bory grown with different amounts of NH 4 þ were investigated. Plants of uniform size were grown on full strength Smart and Barko medium with different NH 4 þ concentrations (0.5, 1, 5, 10 and 15 mM) and incubated in a greenhouse for four weeks. Salvinia cucullata grew well in the medium with 0.5–1 mM NH 4 þ with a relative growth rate of 0.11–0.12 d 1 without exhibiting NH 4 þ toxicity symptoms. With an NH 4 þ concentration above 5 mM, plant growth was suppressed and signs of NH 4 þ toxicity were observed. NH 4 þ toxicity symptoms were obvious in plants supplied with 10 mM and 15 mM NH 4 þ . 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 15 mM NH 4 þ . This species had a high uptake rate even though the NH 4 þ concentrations increased, making it an ideal candidate for growth in eutrophic environments. The high NH 4 þ 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. & 2011 Elsevier Inc. All rights reserved. 1. Introduction The high growth rate of the human population increases water pollution caused by human activities and demand for water. Both housing and agriculture activities increase the amount of nutrient runoff into rivers and lakes (Jackson et al., 2001). Nitrogen is generally found in the water column in the form of nitrate (NO 3  ) and ammonium (NH 4 þ ). Under anoxic condition NH 4 þ becomes an abundant N form for plants and may increase to a level that is harmful to aquatic macrophytes especially in aquatic ecosystems where high levels of NH 4 þ are released from intensive use of agricultural fertilizer and animal waste from farmlands. High NH 4 þ concentration can be a stressor that affects aquatic macro- phytes in eutrophic lakes or wetlands (Lampert and Sommer, 1997). Plants’ response to various NH 4 þ concentrations is different among species. Sensitive species show NH 4 þ toxicity symptoms such as stunted growth, chlorosis, rotted roots and dead plants in the water column (Britto and Kronzucker, 2002; Cao et al., 2007, 2009). In contrast, tolerant species still grow well at high NH 4 þ concentrations and consequently completely dominate aquatic ecosystems. The free floating aquatic fern Salvinia cucullata Roxb. Ex Bory is native to South and Southeastern Asia. It has a wide distribution in India, Indochina, Malaysia to Sumatra and Thailand. The plant is fast growing and has a high dispersal rate (Napompeth, 1989; McFarland et al., 2004). The plant can grow in various environ- ments especially in nutrient enriched water. As a result, it can dominate aquatic ecosystems and may alter plant community structure and ultimately ecosystem functions (McFarland et al., 2004; Ensbey, 2009). Because of its high growth rate, it rapidly spreads by fragmentation so species of Salvinia can create pro- blems in many countries. Dense mats of Salvinia spp. can obstruct transportation, irrigation and hydroelectric production. However, many of them have been used for N removal from wastewater. This property is a positive characteristic when nutrient removal in an aquatic ecosystem is required. Salvinia cucullata has a high growth rate especially when grown in NH 4 þ enriched water (Jampeetong et al., in press). However, under high N loading the plants may suffer from NH 4 þ toxicity and mineral deficiency. Information on growth and ability to remove NH 4 þ , a primary cause of eutrophication, is lacking. Hence, the objective of this study is to assess the growth of Salvinia cucullata and its effectiveness in N removal under different NH 4 þ concentrations Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/ecoenv Ecotoxicology and Environmental Safety 0147-6513/$ - see front matter & 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.ecoenv.2011.12.003 n Corresponding author. Fax: þ66 53 892259. E-mail address: ajampeetong@yahoo.com (A. Jampeetong). Ecotoxicology and Environmental Safety 79 (2012) 69–74