Ectomycorrhizas and putative ecto- mycorrhizal fungi of Afxelia africana Sm. and Uapaca guineensis Müll.. Arg. in southern Senegal BY D. THOEN'i2 AND A. M. BA' 'Laboratoire de Microbiologie des Sols, ORSTOM, B.P. 1386, Dakar, Senegal 'Fondation Universitaire Luxeinbourgeoise (FUL), rue des Diporte's, No. 140, B-6700 Arlon, Belgium (Received 3 April 1989; accepted 18 August 1989) SUMMARY Ectomycorrhizas and ectomycorrhizal fungi of Afielia africana Sm. and Uapaca guineensis Müll. Arg. are reported in forests of southern Senegal. Ectomycorrhizas occurred in dry and wet conditions, at different soil contents of available phosphorus (0-17.5 pg g-'). U.guineensis was confined to groundwater forests. Individual trees had both ecto- and endomycorrhizas, A. africana grew scattered in semi-evergreen and riverside forests, whereas in the woodland it formed larger patches and could dominate the canopy. Eighteen putative ectomycorrhizal fungi grew under U..guineensis and thirty-one under A. africana. Only six species were common to both trees, indicating an ecological and/or taxonomical selection. The fungi belonged to the following Orders : Russulales (16), Boletales (2), (2), (1l), Agaricales (9), Cnntharellales Sclerodermatales Hymenogastrales (l), Gnutieriales (l),Aphyllophorales (1). Some of them had a wide Sudano-Zambezian or Guineo-Congolian distribution and reached their northern limit in Senegal. Key ivords : Ectomycorrhizal fungi, tropical trees, dual symbiosis, ectomycorrhizas, \V. Xfrica. Afielia bella in Nigeria (Redhead, 19686). A Russula ISTROD L'CT I O S and an unknown member of the Hygrophoraceae During the last decade there has been renewed were recorded under A. bella in Ghana (Alexander, interest in tropics1 mycorrhizas. Field observations 1985). In the Zambian miombo woodland the main have increased the number of tropical tree genera putative ectomycorrhizal fungi belonged to the known to form ectomycorrhizas (ECM) (Newbery genera Amanita, Cantlzarellus, Lactarius and Russula et al., 1988). In tropical Africa, ECM were reported (Högberg & Piearce, 1986). an-rong the follo\ving families (or subfamilies) and In this paper \ve present observations on the genera: Carsalpinioideae (Afielia, Aphanocalys, ectomycorrhizal fungi and the ECM of -4fidia Antltorrotlta. Berlitria, Bracfiystegia, Didelotia, Gil- africana Sm. and L*Tapacaguineensis Müll. Arg. The bert;ocierccfi.orr. lsoberliru'a, Julberizardia, Micro- ectomycorrhizal status of A. africana in Ghana berlinici, 3~[~riopelalaiithlls,Paramacrolobiunt, Tetra- (Jenik & Mensah, 1967) and in Sigeria (Redhead, berlittia), Dipterocarpaceae (Marquesia, Monotes), 1968a) has already been reported. The mycorrhizal Euphorbiaceae (Uapaca), Papilionoideae (Peri- status of U. gubreensis is reported now for the first copsis), Proteaceae (Faurea) (Peyronel & Fassi, 1957. time. 1960; Fassi S; Fontana, 1961, 1962; Jenik & &lensah, 1967; Redheac!, 1968a, 19686,1980. 1982: Hagberg I0.2 ,A .A l'lif< .AS KT 0 115 & Sylund, 1981; Högberg, 1982; Högberg & SI 1 I.< I) \I I{ Sites Pieíírctr, ; Alesander Sr Högberg, 1986 ; Xles- 1980\YS?; , 1985, Newbery et al., 1988). However, The forests rungr from the Guinean to the Sudano- a few putative ectomycorrhizal fungi were Guinean type (Fig. 1 and 'Table 1). -Innual rainfall tified and their host specificity is poorly docu- !varies from an Lnwage of 1200 mm to more than . .4n Inocj& SP. was observed apociated with 1700 n-rm (period 193 1-60). In recent years, these I Fonds Documentalre ORSTOM za,& Fonds Documentaire ORSTOM ~l~ll~~l~~~~~~ll~~l~~~~~l~~~~~~~l~llO100141 91 EX: cote: 42 WY II- 1 I L 1 + ., J) 7. 550 D. Thoen und A.M. Ba - -- -- - --I --- M AU RITAN IA Z a O Dakar< SENEGAL \ 700 km 16"30 16" I GAMBIA I 1 20 km 55 1 - . -- Mean annual Site Altitude rainfall (mm) Phytogeographical no. Locality (m) (1931-60) region or domain Soil type 1 Santiaba Manjak 10 1700-1 800 Guinean Hydromorphic soil (12"24'N, 16'35'U') and latosol 600-1 îO0 ,I 13.1:\ ottes i o 1 Guineo-Sudanian Latosol (12"29'N, 16'17'W) III Djibelor 10 1500-1 600 G uineo- Sudanian Latosol (12" 34'N, 16" 17'W) IV Tobor 20 1400-1 500 Sudano-Guinean Latosol (12" 43' N, 16" 14' W) Y Tendouk 20 1400-1500 Sudano-Guinean Latosol (1 2" 46' N, 16" 27' W) I Diegoun 25 1400-1500 Sudano- Guinean Latosol (12" 49' N,16" 19' W) \.' II Kalounayes 30 1300-1400 Sudano-Guinean Latosol (12"50' N,16" 8' W) VI11 Thiara 40 1200-1 300 Sudano-Guinean Grey ferruginous (12" 44' N, 14" 32'W) soil IX Dakateli 80 1200-1 300 Sudano-Guinean Hydromorphic soil (12" 27' N, 12" 40' W) 2) Table 2. Main physico-chemical characteristics of the upper soil layer (site no. as in Table Site no. Ia* Ib** II* III* IV* V* VI* VII' VIII* 9-8 Clay (Yo) 4.2 12.6 3.7 6.0 4.5 5-3 1-6 12.7 Silt (yo) 26.5 18.6 31-0 9.4 8.9 32-7 368 22.6 23.2 Sand (%I 670 65.0 67.9 83.9 795 61.0 566 74.3 63.1 pH (water) 61 4.0 5-8 49 5.8 6.2 5-5 61 5.1 5.3 PH(KCU 5.6 3.5 5.4 3.8 5-0 5.0 5.5 47 Carbon (Yo) 11-7 31-9 29.4 41 11.7 109 19.6 15.2 25 15.1 Nitrogen (%) 1.0 2-5 03 0.7 1*o 1.7 1-5 1.1 C/N 12 13 12 12 13 11 12 10 14 Total phosphorus 83 148 223 19 24 109 122 135 140 g-7 Available phosphorus 0.0 4.4 13-1 3-9 8.3 4.4 4.4 8.7 17.5 95 9 97 - 85 78 70 83 56 ~ ~~ * Soil samples taken under Afielia africana: **, soil sample taken under Uapaca guineensis; ***, metallic cations percentage saturation of soil. figures have decreased by an average of approx. (1982) for site I, and Vanden Berghen (1984) for site 100-200 mm. The rainy season extends from June to VIL Site VI11 has a typical woodland structure with October and is followed by a marked dry season. a tree layer and a well developed grass layer. Afielia The Sudano-Guinean tree Afzelia africana has a africana is the dominant tree, accompanied by wide range of habitats. In the semi-evergreen forests Erythrophhum africamm (Welw.) Harms, Daniellia and in the riverside forests it is scattered (Fig. 2a), oliveri (R.) Hutch. & Dalz., Cordyla pinnata (Lepr.) whereas in the woodlands it occurs in small or large Mil.-Red., Pterocarpus erinaceus Poir., Burkea afri- patches and then dominates the canopy. It is present cana Hook., Prosopis africana (G. & Perr.) Taub., in all the sample sites. Uapaca guineensis is a relict Combretum spp. Site IX is a small riverside forest Guinean tree in Senegal, confined to azonal, hydro- where individuàls of U. guineensis arid A. africana morphic soils. In the study area, it is abundant on the grow together. Surrounding vegetation is a degraded border of a wet depression (site i) and scattered in a woodland. Under U. guineensis, the grass layer is riverside forest (site IX). Stilt roots are an adaptation absent and the litter layer is abundant (Fig. 2b), to waterlogging (Fig. 26). whilst under A. africana, the grass layer is well Soils, flora and/or vegetation were described by developed and the little layer is shallow (Fig. 2a). Doumbia (1966) for sites I-VI, Schneider & Sambou Table 2 shows the main characteristics of the upper soil layer (0-20 cm) from sites I to VIlI. ensis. Noteworthy is the great diversity of orders, - . U nde F A. c+ieana-t-h esoi-Is-a reaci d- to- mo-derateIFgenera ~än~-species'tn-'€~êfÜñgärSpeSt~Üm~~t h-K acid ; the metallic cations saturation coefficient (V) africana and U. guineensis. The most represented ranges between 70 !//;o and 97 yo. Under U. guineensis, orders are the Russulales (1 6 species), the Boletales the soil is very acid (pH 4) and poorly saturated (V = (11 species) and the Agaricales (9 species). Several 9 "b). As the water level fluctuates greatly during the fungi, such as Amanita spp. and Russula spp. are still year, leaching occurs causing an important loss of undescribed in Africa and might belong to new nutrients. The content of available phosphorus in species. Xoteworth!. also is the presence of hypo- lo\\ the soil (Olsen method) is \.cry or moderare. The geous fungi. rivo under U. giiiiieeiisis and one under highest availa!)lr phosphorus level (17.5 pg gel) is A. africana. 'These hypogeous species are so far obsrr\.ed in the .qfze/ia nfricnnn woodland of site undescribed. They are the first records of hypogeous !Ir111. fungi in Senegal and perhaps for any tropical forest of West Africa. Only six fungi are common to both A. africana and L'. guineensis. It is, however, Sa?rip ling untimely to assess any host specificity. Sampling was carried out during the rainy season. Table 4 shows that some fungi have a wide Superficial roots were excavated, starting from the distribution in tropical Africa. The fungi of il. trunk and working towards the ultimate fine roots. africana and U.guineensis are, however, not found in Rootlets (1-5 g) were fixed in formaldehyde-acetic the Sudano-Sahelian region, where endomycorrhizal acid (FAA) (Johansen, 1940). For young seedlings trees such as Acacia spp. are dominant. They reach the whole root system was fixed. their northern limit in Senegal in the Sudano- The fine roots were examined under a dissecting Guinean region. microscope. Rootlets covered by a fungal sheath The dependence of the ectomycorrhizal fungi on were gently escised and washed under tap water. host trees is high.