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Leaf and canopy CO2 assimilation in a West African humid savanna during the early growing season

Published online by Cambridge University Press:  10 July 2009

X. Le Roux  and
P. Mordelet
X. Le Roux
Affiliation:
Ecole Normale Supérieure, Laboratoire d'Ecologie (URA 258 CNRS), 46 rue d'Ulm, 75230 Paris Cedex 05, France
P. Mordelet
Affiliation:
Ecole Normale Supérieure, Laboratoire d'Ecologie (URA 258 CNRS), 46 rue d'Ulm, 75230 Paris Cedex 05, France
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Abstract

Leaf and grass canopy photosynthetic rates were measured in a West African humid savanna during several stages of the early growing season. The results obtained on the dominant grass species Hyparrhenia diplandra and data published previously show that C4 savanna grasses exhibit a remarkably high leaf photosynthetic capacity despite their low nitrogen content. A variation of leaf photosynthetic capacity in relation to leaf rank on stems is observed which is interpreted by ageing and shading effects within the canopy. Seasonal variations of the canopy CO2 assimilation rate is explained in relation to variations of leaf area index and canopy nitrogen content. Despite low nitrogen content or low leaf area index, maximum canopy net photosynthesis was high (24 μmol CO2 m-3 s-1 for LAI = 1.5). The high photosynthetic nitrogen use efficiency exhibited by leaves of humid savanna grass species is a major attribute explaining high photosynthetic rates of the grass canopy in this environment. This result sustains the emerging opinion that tropical savannas could be highly productive despite the generally low nutrient status they experience.

Keywords

Côte d'IvoiregrassHyparrhenia diplandranitrogen use efficiencyphotosynthesissavanna
Type
Research Article
Information
Journal of Tropical Ecology , Volume 11 , Issue 4 , November 1995 , pp. 529 - 545
Copyright
Copyright © Cambridge University Press 1995

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