Multi?Host Ectomycorrhizal Fungi Are Predominant in a Guinean Tropical
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Environmental Microbiology (2010) 12(8), 2219–2232 doi:10.1111/j.1462-2920.2010.02183.x Multi-host ectomycorrhizal fungi are predominant in a Guinean tropical rainforest and shared between canopy trees and seedlingsemi_2183 2219..2232 Abdala Gamby Diédhiou,1,2*† Marc-André Selosse,3 lings harboured a similar fungal community. These Antoine Galiana,1 Moussa Diabaté,1,4 findings suggest that there was a potential for the Bernard Dreyfus,1 Amadou Moustapha Bâ,1,5 formation of common mycorrhizal networks in close Sergio Miana de Faria6 and Gilles Béna1 vicinity. However, no significant difference was 1Laboratoire des Symbioses Tropicales et detected for the d13C and d15N values between seed- Méditerranéennes, UMR113 – INRA/AGRO- lings and adults of each ECM plant, and no ECM M/CIRAD/IRD/UM2 – TA10/J, Campus International de species exhibited signatures of mixotrophy. Our Baillarguet, 34398 Montpellier Cedex 5, France. results revealed (i) variation in ECM fungal diversity 2Laboratoire Commun de Microbiologie, according to the seedling versus adult development IRD/UCAD/ISRA, BP 1386 Dakar, Sénégal. stage of trees and (ii) low host specificity of ECM 3Centre d’Ecologie Fonctionnelle et Evolutive (CNRS, fungi, and indicated that multi-host fungi are more UMR 5175), Equipe Interactions Biotiques, 1919 Route abundant than single-host fungi in this forest stand. de Mende, 34293 Montpellier Cedex 5, France. 4Institut de Recherche Agronomique de Guinée, Division Introduction des Cultures Pérennes, Programme Recherche Forestière, BP 1523, Conakry, République de Guinée. Ectomycorrhizal (ECM) symbiosis involves soil fungi and 5Laboratoire de Biologie et Physiologie Végétales, tree roots. It provides mineral nutrients, water and protec- Faculté des Sciences Exactes et Naturelles, Université tion against pathogens to the plant which, as a reward, des Antilles et de la Guyane, BP 592, 97159 provides carbon to its fungal partner (Smith and Read, Pointe-à-Pitre, Guadeloupe, France. 2008). Each individual tree associates with several ECM 6Embrapa Agrobiologia km 47, antiga estrada Rio-São fungal species, while fungal species display variable Paulo, Seropédica 23851-970 Brazil. levels of specificity, ranging from highly specific species to generalists (= multi-host; Selosse et al., 2006; Smith Summary et al., 2009). Multi-host ECM fungi are often abundant, at The diversity of ectomycorrhizal (ECM) fungi on adult least in Holarctic and Mediterranean ECM communities trees and seedlings of five species, Anthonotha fra- (e.g. Kennedy et al., 2003; Dickie et al., 2004; Richard grans, Anthonotha macrophylla, Cryptosepalum tet- et al., 2005), but sometimes display host preferences as raphyllum, Paramacrolobium coeruleum and Uapaca shown in mixed Japanese forests (Ishida et al., 2007), esculenta, was determined in a tropical rain forest of and Tasmanian sclerophyllous forest (Tedersoo et al., Guinea. Ectomycorrhizae were sampled within a 2008). Some fungal taxa are more specific, e.g. suilloids, surface area of 1600 m2, and fungal taxa were identi- which are almost entirely restricted to Pinaceae (Bruns fied by sequencing the rDNA Internal Transcribed et al., 2002), and associates of Alnus (Tedersoo et al., Spacer region. Thirty-nine ECM fungal taxa were 2009) in Holarctic regions. determined, of which 19 multi-hosts, 9 single-hosts Very few studies have addressed the question of spe- and 11 singletons. The multi-host fungi represented cific versus multi-host abilities in tropical forests, where 92% (89% when including the singletons in the analy- ECM associations remain little studied (Alexander et al., sis) of the total abundance. Except for A. fragrans, the 1992; Alexander and Lee, 2005; Tedersoo et al., 2007a). adults of the host species displayed significant differ- In tropical Africa, there are currently few reports of ECM entiation for their fungal communities, but their seed- host preferences, particularly in mixed forests. In this region, ECM trees include Caesalpinioideae, Phyllan- Received 14 May, 2009; accepted 21 December, 2009. *For thaceae as well as some Dipterocarpaceae, Proteaceae correspondence. E-mail [email protected]; Tel. (+221) 33 and Sapotaceae (Högberg and Piearce, 1986; Newbery 849 33 32; Fax (+221) 33 849 33 02. †Present address: Laboratoire Commun de Microbiologie, IRD/UCAD/ISRA, BP 1386 Bel-Air, Dakar, et al., 1988; Torti and Coley, 1999; Ducousso et al., 2004), Senegal. but ECM fungal communities and their links with © 2010 Society for Applied Microbiology and Blackwell Publishing Ltd 2220 A. G. Diédhiou et al. composition of the plant community remain little studied. not yet been used to test for the origin of seedlings’ Fruit body collections from mixed African forests have carbon. already suggested that numerous ECM fungi are multi- In the Southern Guinea rainforests (West Africa), Cae- host (Sanon et al., 1997; Rivière et al., 2007). Thoen and salpinioideae and Phyllanthaceae trees are the most Bâ (1989) suspected host effects on ECM fungi collected abundant native ECM species, growing in mixed patches, under Afzelia africana and Uapaca guineensis in southern which raises the possibility of some fungal sharing. A high Senegal. Nevertheless, fruit body survey cannot predict regeneration occurs under adult trees, strongly suggest- the ECM association patterns at the root level, because ing whether any ‘nurse effect’ occurs, that is: (i) do coex- below-ground fungal diversity and abundance differ from isting trees and seedlings harbour the same fungal those observed above-ground (Richard et al., 2005). communities? and/or (ii) do ECM fungi provide carbohy- Inoculation of seedlings demonstrated that some African drates to seedlings? In this typical primary forest area, we fungal isolates are compatible with multiple tree species first described the fungal diversity on ECM root tips, to (Diédhiou et al., 2005). Hence, in situ studies of ECM assess ECM association patterns among the five domi- diversity at root level are still required to assess the diver- nant host species and between both development stages, sity and specificity (versus host sharing) of the ECM i.e. adults versus seedlings. Second, in order to test fungal community from tropical Africa. whether some carbohydrates were transferred to seed- Some ECM tropical tree species tend to aggregate in lings, we compared the 13C and 15N contents of the latter patches where they dominate together or alone (Newbery with those of adult trees, fruit bodies of ECM fungi and et al., 2004; Alexander and Lee, 2005), surrounded by surrounding AM tree species. trees forming arbuscular mycorrhizae (AM; McGuire, 2007). In the Korup National Park (Cameroon), ECM trees form up to 70% of local patches (Newbery et al., 1997); Results similarly, the ECM Gilbertiodendron dewevrei represents Ectomycorrhizal diversity more than 90% of trees in some stands of the Congo basin, with abundant seedlings (Hart et al., 1989). Such From 12 adult trees (Fig. 1) and 138 surrounding seed- mono- or oligo-dominant stands suggest efficient regen- lings, 150 and 190 root samples were, respectively, col- eration under adults. It has been claimed that adult trees lected (Table 1). From these samples, 362 ECM tips were could provide ECM inocula to seedlings, in the form of obtained, and 293 were successfully amplified and already established (and perhaps even already nour- sequenced (81%, Table 1); only 10 ECM tips exhibited ished) fungi. This likely favours the survival of seedlings in two different Internal Transcribed Spacer (ITS) sequences temperate ecosystems (Nara, 2006) and tropical ones at the same time. The 303 different ITS sequences (Onguene and Kuyper, 2002; McGuire, 2007). However, obtained represented 39 ECM fungal taxa (i.e. diverging no data are available on fungal sharing between adults sequences) from seven fungal families: Boletaceae, Cla- and seedlings in the latter ecosystems. vulinaceae, Russulaceae, Sclerodermataceae, Thelepho- Besides an indirect interaction (with adults paying the raceae, Tricholomataceae and three other undetermined cost of the fungus more than the seedlings), facilitation families (Table 2). can also occur thanks to carbon and nutrients transferred from adults to seedlings by way of mycorrhizal networks, Ectomycorrhizal abundance and distribution interconnecting root systems of the same or different among host species species (Simard et al., 1997). Labelling experiments have shown in both laboratory and field conditions that carbon Among the 39 ECM taxa, 20 (including 11 singletons) and nutrients can be transferred between plants through were found on a single host species and 19 were multi- mycorrhizal networks (Selosse et al., 2006). However, the host: six were shared by the five tree species, two by four, role of the hyphal pathway during carbon movement, and two by three and nine by two tree species (Table 2). Each the physiological or ecological relevance of inter-plant tree species associated with 10–15 multi-host ECM fungal transfers remain controversial (e.g. Fitter, 2001; Wu et al., taxa, 2–3 single-host ECM fungal taxa, and 1–5 single- 2001). Natural abundance of stable isotopes has given tons. To compare the abundance of single-host ECM taxa increased support to such exchanges, at least in oversto- and multi-host ECM taxa, the singletons were excluded rey receiver species in forest ecosystems (Selosse and from the analysis. Therefore, from the considered 292 ITS Roy, 2009). Such plants receiving carbohydrates from sequences, the multi-host ECM taxa represented