Carbon isotope ratios (δ<sup>13</sup>C) were obtained from foliage and branch wood samples of Acacia tortilis grown with and without microbial inoculation, on three semi-arid sites in Kenya. δ<sup>13</sup>C ratios were higher in trees grown on the two drier sites than on the wetter site. In addition, δ<sup>13</sup>C ratios of seedlings inoculated with a mixed microbial inoculum (VA mycorrhiza with rhizobia) were higher than un-inoculated controls at the wetter site. These preliminary results suggest that Acacia tortilis trees growing on drier sites display relatively high water-use efficiencies, and that in some situations microbial inoculation may increase water-use efficiency of out-planted trees.
Journal of Arid Environments (1996) 34 (3) 325-330