Résumé
In the African tropical dry woodlands, very few woody species are able to thrive both on Macrotermes termite mounds and in the surrounding matrix. Dalbergia boehmii is one such broad-niched species. In a previous study, populations on and off mounds were found to have different functional trait values. Here, in two reciprocal transplant experiments, both in situ and ex situ (pot experiment) we test whether the plants from mounds and from the matrix have evolved genetically divergent traits and are locally adapted (edaphic ecotypes), or whether trait differences arise from phenotypic plasticity. Growth, survival and morphological functional leaf traits were monitored. Seedling survival did not differ between plants of different origins and habitats. No constitutive difference or no heritable features were found between the plants of the two origins. However, functional traits varied between habitats in the in situ experiment, with higher specific leaf area (SLA) and lower leaf dry matter content values on termite mounds, indicating plastic response. The magnitude of the plastic response was larger in situ compared to the pot experiment, suggesting that other ecological factors, in addition to soil, drive trait plasticity. We conclude that the broad niche of the species is due to its ability to express adaptive phenotypic plasticity, not to locally adapted genotypes.