Characterization of the variability of the daily course of leaf water potential in the dominant shrub species within Sahelian fallows in south-west Niger

Around Niamey, in Niger, the shrub Guiera senegalensis dominates all of the fallows in almost totally monospecific stands. The species has a strong resprouting ability enabling it to survive cutting when clearing land for crops, whereas all other species succumb to cutting. However, in this dry environment (560 mm of annual rainfall from June through September), this remnant-increaser species has to cope with variations of available water in space and time. The daily course of its water status is an indicator of the variation of the intensity of water flux between the soil, vegetation and atmosphere, and it is often estimated with Soil Vegetation Atmosphere Transfer (SVAT) models. essed the water status of G. senegalensis through its daily cycle leaf water potential (Ψ), using six populations representative of the local diversity by measuring three shrubs per population on two excised leaves per shrub for each measurement. We made our measurements over two vegetative cycles (from July 1994 to December 1995), fortnightly during the rainy season, and once a month during the dry season, until the sample shrubs lost their leaves in their deciduous cycle. d linear models to characterize the daily Ψ cycle of the shrubs, and of the populations during each season. For each population, three sources of variation were considered: the shrub number, the date and the hour in day. Date and hour in day effects are presented as trend surface models defined by the degrees of polynomials and the status of shrub effects. The status of shrub effects characterizes the variability in accounting for environmental conditions. oup of plant populations that explain the least variability in every model as well as the least total variance among the shrubs and between seasons were in locations with the best water supply. Two other groups were defined according to the median and the highest explained variability of Ψ, respectively. For all stations, the most temporal variability is explained by models accounting for the interaction between shrubs and the temporal variation, with the least variability for models that do not account for the shrub effect at all. Models accounting only for the additive effect of shrubs explain intermediate values. The models used herein indicate the large range of variability in G. senegalensis water status, both for inter- and intra-populations. This high physiological plasticity must contribute to the strong species-dominance stability in its current distribution area.