Résumé
The ‘pure’ effect of aridity on photosynthetic and water-transport strategies is not easy to discern because of large-scale correlations between precipitation and temperature. We analyse traits collected along an aridity gradient in Ghana, West Africa, that shows very little temperature variation, in an attempt to disentangle thermal and hydraulic influences on plant traits. Theoretical predictions of the variation of key plant traits along the gradient are tested with field measurements. Most photosynthetic traits show trends consistent with theoretical predictions, including higher photosynthetic rates in the drier sites, and an association of higher photosynthetic rates with greater respiration rates and greater water transport. Hydraulic and leaf-economic traits show less consistency with previous theories, however. In particular the relationship between the sapwood-to-leaf-area ratio (AS/AL) and potential specific hydraulic conductance (Kp) is found to differ from that shown in a global dataset. Nonetheless, the link between photosynthesis and water transport holds: species with both higher AS/AL and Kp (implying greater water transport) (predominantly deciduous species found in drier sites) tend to have both higher photosynthetic capacity, and lower leaf-internal CO2, than others. These results indicate that aridity is a primary driver of the spatial pattern of photosynthetic traits, while plants show a greater diversity of water-transport strategies to support higher photosynthetic rate in arid environments.