Effects of water stress and substrate fertility on the early growth of Acacia senegal and Acacia seyal from Ethiopian Savanna woodlands

摘要

Key message Acacia senegal and Acacia seyal present different drought stress coping mechanisms that are independent of substrate fertility. Higher substrate fertility increased aboveground plant growth, even with low watering. Abstract The potential of native African tree species for agriculture and forestry have not yet been thoroughly investigated. In this experiment, we studied the early growth of Acacia senegal and Acacia seyal plants in an experiment with two substrates of contrasting fertility (low/high) and two watering frequency regimes (low = 24.40 l/m(2) per month, high = 48.80 l/m(2) per month). Our objectives were: (1) to study whether the mechanisms by which nutrients affect plant growth at the seedling stage operate differently when water availability varies, and (2) to look for differences in the growth strategies of the two species in early stages. Higher substrate fertility increased aboveground plant growth at the expense of roots in both water regimes. Though water stress significantly limited growth under both soil conditions, substrate fertility effects were relatively higher in plants with low water supply than in those with high water supply. However, even with low resources the root-to-shoot ratio was between 0.7 and 0.9, plants presented adequate nutrition and no mortality was observed. This indicates opportunistic mechanisms forwater and nutrient use. A. seyal showed the lowest negative pre-dawn stem water potential value (-0.15 MPa) and shed nearly all leaves in the hottest month of the assay, which suggests a different drought avoidance strategy and adaptation to water stress than A. senegal. Both species can be produced successfully in local nursery conditions and can survive and thrive with low watering. The study also demonstrated that fast growing genotypes can be effectively isolated in nursery conditions.