Biome-specific effects of nitrogen and phosphorus on the photosynthetic characteristics of trees at a forest-savanna boundary in Cameroon.

Photosynthesis/nutrient relationships of proximally growing forest and savanna trees were determined in an ecotonal region of Cameroon (Africa). Although area-based foliar N concentrations were typically lower for savanna trees, there was no difference in photosynthetic rates between the two vegetation formation types. Opposite to N, area-based P concentrations were-on average-slightly lower for forest trees; a dependency of photosynthetic characteristics on foliar P was only evident for savanna trees. Thus savanna trees use N more efficiently than their forest counterparts, but only in the presence of relatively high foliar P. Along with some other recent studies, these results suggest that both N and P are important modulators of woody tropical plant photosynthetic capacities, influencing photosynthetic metabolism in different ways that are also biome specific. Attempts to find simple unifying equations to describe woody tropical vegetation photosynthesis-nutrient relationships are likely to meet with failure, with ecophysiological distinctions between forest and savanna requiring acknowledgement.

Craterispermum capitatum and C. gabonicum (Rubiaceae): two new species from the Lower Guinean and Congolian Domains.

Craterispermum capitatum and C. gabonicum, two new species of Rubiaceae, are described from the Lower Guinea and Congolian Domains. Detailed descriptions and distribution maps are provided for each species, their conservation status is assessed and their taxonomic affinities are discussed. Craterispermum gabonicum is unique within the genus because of the strong dimorphism in brevistylous and longistylous flowers and inflorescences. We hypothesize that this species shows some form of dioecy. The distribution of C. capitatum shows a wide disjunction: the species is present in the Lower Guinean and Congolian Domains but absent from Gabon and South Cameroon. An identification key for the Craterispermum species present in the Lower Guinean and Congolian Domains is given.

Résumé Craterispermum capitatum et C. gabonicum, deux nouvelles espèces de la famille des Rubiaceae, des Domaines Bas Guinéen et Congolais sont décrites. Des descriptions détaillées et des cartes de distribution sont données pour chacune des espèces, leur statut de conservation est évalué et leurs affinités taxonomiques discutée. Craterispermum gabonicum est unique dans le genre en raison d'un dimorphisme avéré entre les fleurs, mais aussi les inflorescences brévistyles et longistyles. L'hypothèse de l'existence d'une tendance vers la dioécie chez cette espèce est émise. La distribution C. capitatum présente une importante disjonction: l'espèce est présente dans les Domaines Bas Guinéen et Congolais, mais absente au Gabon et au sud du Cameroun. Une clé d'identification pour les espèces de Craterispermum présentes dans les Domaines Bas Guinéen et Congolais est donnée.