Forest Ecology and Management, 29 (1989) 311-314 Elsevier Science Publishers B.V., Amsterdam-- Printed in The Netherlands
N e w Nodulating Legume Tree Species from Guinea-Bissau, West Africa JOHAN W E S T E R and PETER H O G B E R G I Department of Forest Site Research, Swedish University of Agricultural Sciences, S-901 83 Umed (Sweden)
(Accepted 20 December 1988)
ABSTRACT Wester, J. and HSgberg, P., 1989. New nodulatinglegumetree species from Guinea-Bissau,West Africa. For. Ecol. Manage., 29: 311-314. Rhizobium-type root nodules were found on roots of mature specimens of seven legume tree species indigenousto West Africa. Nodulation is reported for the first time in Albizia [erruginea and A. zygia.
INTRODUCTION There is an increasing interest in legume trees forming nitrogen-fixing root nodules because of their great potential for soil enrichment in agroforestry and forestry at adverse sites. Up to 1981, only ca. 16% of the legume species (herbaceous and woody) had been examined for nodulation (Allen and Allen, 1981 ). Despite more-recent efforts, notably in Brazil (De Faria et al. 1984, 1987; Magalheas et al. 1982 ), there is a lack of information on the nodular status of m a n y tropical legume tree species (Halliday, 1984; De Faria et al., 1989). We report the result of a minor survey of legume trees found in West Africa. MATERIALSAND METHODS
This survey was made around Bissor~i,Guinea-Bissau, West Africa (12 °00' N, 15°30'W). The vegetation of the area is largely secondary, with cultivated land, secondary grassland and secondary woodland dominating, and with a few remnants of forest.The conversion of forest to wooded grasslands and woodlands have promoted the invasion of tree species typical of the drier Sudanian woodlands to the north (White, 1983). The trees sampled were found in wood1Authorto whom correspondenceshouldbe addressed.
© 1989 Elsevier Science Publishers B.V.
TABLE 1 Indigenous legume tree species found to nodulate in Guinea-Bissau. Species ~
Shape of root nodules 2
Albizia adianthifolia (Schum.) W.F. Wight A./erruginea 3 (Guill. & Pert.) Benth. A. zygia 3 (DC.) J.F. Macbr. Dichrostachys glomerata (Forsk.) Chiov. Erythrina senegalensis DC. Prosopis africana (Guill. & Perr.) Taub. Pterocarpus erinaceus Poir.
elongate and bifurcate elongate, fan-shape and palmate bifurcate or globose? elongate globose elongate, fan-shape and palmate globose
~Nomenclature of species follows Hutchinson and Dalziel (1985). 2Nodule shape according to Allen and Allen (1981). 3New record.
land and fallow vegetation. The rainfall, which is strongly seasonal, averages 1230 m m year-1. The mean annual temperature is 26.3 °C. The free-draining soils of the area are generally classified as Ferric Luvisols (Anonymous, 1977). Root sampling was conducted in October, i.e. at the beginning of the dry season. Roots were traced from the stem bases of identified mature legume trees (Table 1). Suspected root nodules, if found, were preserved in 50% (v/v) ethanol in water. Herbarium specimens of leaves, pods, twigs etc. were collected and are now kept in the herbarium of our department. Samples suspected to be root nodules were later dehydrated in ethanol, embedded in glycol methacrylate (LKB-Produkter AB, Bromma, Sweden), sectioned in 0.5-1-#m-thick cross-sections on a glass knife, mounted, stained in toluidine bleu and examined under light microscopy. RESULTS AND DISCUSSION
All the material sampled and sectioned had a zonal tissue organization typical of root nodules of legume × Rhizobium-type (Allen and Allen, 1981 ), i.e. a central zone with many cells thought to be infected by bacteriods surrounded by a non-infected zone (endodermis plus cortex) containing vascular traces (Table 1; Fig. 1). We did not have the possibility of isolating the bacteria or to confirm nitrogenase activity (C2H2-reduction assay) or nitrogen fixation (15N2-reduction assay ). Due to the clear result of the sectioning work, we are nevertheless convinced that the material collected consists of proper legume × Rhizobium-type root nodules. Root nodules may contain bacterial strains not capable of fixing nitrogen, but theoretical considerations as well as empirical findings support
NEW NODULATINGLEGUMETREES FROMGUINEA-BISSAU
Fig. 1. Cross-sections through root nodules formed by Albizia adianthi[olia (a), A. ferruginea (b), A. zygia ( c ), Dichrostachys glomerata (d), Erythrina senegalensis (e), Prosopis africana (f), and Petrocarpus erinaceus (g). Notation in illustrations: b, zone with cells thought to be infected by bacteroids; v, examples of vascular traces. Scale bars are 200/lm.
JOHAN W'ESTER AND PETER HOGBERG
the assumption that selection in the field favours effective strains (Beringer and Burggraaf, 1986). According to compilations of reports on nodulation (Allen and Allen, 1981; Halliday, 1984; De Faria et al., 1989), root nodules have not previously been observed in Albizia ferruginea and A. zygia. The root nodules observed in A.
adianthifolia, Dichrostachys glomerata, Erythrina senegalensis, Prosopis africana and Pterocarpus erinaceus confirmed earlier reports (Allen and Allen, 1981; Halliday, 1984; Workman, 1986; De Faria et al., 1989). ACKNOWLEDGEMENTS
This study was sponsored by the Swedish International Development Authority (SIDA). We would like to than Miss Lenore Johansson for skilful sectioning work.
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