Occurrence and coexistence of arbuscular mycorrhizal fungi and dark septate fungi in aquatic macrophytes in a tropical river–floodplain system Josy Fraccaro de Marins a, *, Rosilaine Carrenho b , Sidinei Magela Thomaz b a Faculdade Integrado de Campo Moura˜o, Rod. BR 158, Km 207, Jardim Batel, 87300-970 Campo Moura ˜o, PR, Brazil b Departamento de Biologia, Universidade Estadual de Maringa ´, Av. Colombo 5790, Jardim Universita ´rio, 87020-900 Maringa ´, PR, Brazil 1. Introduction The Upper Parana ´ River floodplain is a tropical wetland subject to high seasonal and inter-annual fluctuations in physico-chemical characteristics and biotic components, and this area is very important for biodiversity conservation (Agostinho et al., 2004). The water level fluctuations are a key physical variable for the structure and functioning of this floodplain, where winter is dry with lower water levels, and summer is usually rainy with high water levels. Many plant and animal species are adapted to these fluctuations (Agostinho et al., 2004). Macrophytes are an important component of this floodplain because they supply organic matter for aquatic and terrestrial organisms and they increase the physical and biological complex- ity of aquatic habitats that provide high diversity of fish and invertebrates (Lansac-Toha et al., 2003; Agostinho et al., 2004). Recent surveys indicate the presence of over 118 species of macrophytes in the entire floodplain, belonging to different taxonomic groups (bryophytes, pteridophytes and angiosperms) and all life forms (emergent, floating leaved, free-floating, free- submersed and rooted submersed; S.M. Thomaz et al., unpublished data). Many investigations carried out in wetlands have recorded the presence of arbuscular mycorrhizal fungi (AMF) in the roots of several species of aquatic macrophytes (Beck-Nielsen and Madsen, 2001; Sraj-Krzic et al., 2006; Radhika and Rodrigues, 2007), suggesting that these microorganisms play an important role in nutrient uptake for these plants. The mycorrhizal fungi belonging to Glomeromycota are obligatory symbionts that colonize the root cortex of plants and form arbuscules, structures responsible for nutrient exchange between the macro- and micro-symbionts (Schu ¨ bler et al., 2001). The Glomeromycetes are considered the oldest group of mycorrhizal fungi, and they are known to be associated with most terrestrial plants belonging to diverse taxonomic groups (Wang and Qiu, 2006). It was also shown that, similar to what occurs in the terrestrial habitats, these fungi are important for transferring nutrients (especially phosphorus) to plants in aquatic habitats (Wigand and Stevenson, 1997). The occurrence of dark septate fungi (DSF), a group of fungi considered mycorrhizal by some authors (Jumpponen, 2001), was Aquatic Botany 91 (2009) 13–19 ARTICLE INFO Article history: Received 4 July 2008 Received in revised form 23 December 2008 Accepted 5 January 2009 Available online 10 January 2009 Keywords: Arbuscular mycorrhiza Co-occurrence Dark septate fungi Tropical macrophyte ABSTRACT In this study, carried out in four water bodies in the Upper Parana ´ River floodplain, we assessed the occurrence of root colonization by arbuscular mycorrhizal fungi (AMF) and dark septate fungi (DSF), as well as the AMF species richness associated with 24 species of aquatic macrophytes belonging to different life forms. AMF were found in nine species of macrophytes and DSF in 16 species among the 24 investigated. AM colonization occurred mainly in eudicotiledons (five of the six species evaluated) and the Paris morphology was the most common type. Co-occurrence of AMF and DSF was observed in seven species of macrophytes (Commelinaceae sp. 1, Limnobium laevigatum (H.B.K. ex Willd) Heine, Hygrophila cf. costata, Myriophyllum brasiliense (Camb), Polygonum acuminatum Kunth, P. ferrugineum Wedd and P. stelligerum Cham). Four species of macrophytes (Pistia stratiotes L., Eichhornia crassipes (Mart.) Solms, Egeria najas Planch and Nymphaea amazonum Mart. & Zucc) were not colonized by any type of fungi. In total, 27 morphotypes of AMF were recorded, and spores occurred both in the rhizosphere of macrophytes whose roots were internally colonized by AMF and in non-colonized macrophytes. Acaulospora delicata, Acaulospora aff. laevis, Acaulospora longula, Glomus lamellosum, Glomus luteum and NID 1 (a non-identified species) were the most frequent species. Samples collected close to the roots of N. amazonum had the highest AMF richness (20 species), but this plant was not colonized by fungi. A species richness curve indicated that more root-associated fungi than reported here are likely present in this floodplain. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +55 44 8812 6338. E-mail address: josymarins@hotmail.com (J.F. de Marins). Contents lists available at ScienceDirect Aquatic Botany journal homepage: www.elsevier.com/locate/aquabot 0304-3770/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.aquabot.2009.01.001