Variability of initial growth, water-use efficiency and carbon isotope discrimination in seedlings of Faidherbia albida (Del.) A. Chev., a multipurpose tree of semi-arid Africa. Provenance and drought effects

The panafrican provenances of Faidherbia albida display contrasting growth and survival rates in semi-arid zones of western Africa, when they are compared in multi-local field trials. In order to identify some potential causes for such differences, we recorded the genetic variability of ecophysiological traits (including water-use efficiency, W, and carbon isotope discrimination, Delta) in seven provenances from contrasting habitats of western and south-eastern Africa. Provenance and drought effects were tested on potted seedlings in a greenhouse. After 6 months, the total dry mass of the well-irrigated seedlings ranged from 31 to 86 g, and the total water-use from 8 to 18 kg. Both initial growth and water consumption were strongly correlated with leaf area. W displayed a significant inter-provenance variability, and exhibited the highest values in the south-east African provenances, which were the most vigourous, but also presented the poorest survival rates in field trials. It was negatively correlated with the leaf-to-total dry mass ratio, LMR, and to Delta. The mild drought significantly reduced gas-exchange rates, leaf area, growth, water-use, specific leaf area, and Delta, in all provenances. It also increased the intrinsic water-use efficiency, Alg, and the root-to-total dry mass ratio, but did not affect W or LMR. No provenance x drought interaction was found in any variable. The initial rate of leaf area establishment probably plays a major role in explaining the contrasting water-use strategies of the provenances. ((C) Inra/Elsevier, Paris.).