Inoculation of leguminous trees with rhizobia and VA mycorrhizal fungi

Many leguminous trees are tripartite symbioses composed of the plant, Rhizobium bacteria, and vesicular-arbuscular (VA) mycorrhizal fungi. However, few field studies have examined the efficacy of inoculating tree legumes with microsymbionts. A Rhizobium inoculation trial was run with Leucaena leucocephala and Acacia pennatula at two sites in Mexico. Results showed that inoculated plants of both species exhibited greater growth than uninoculated controls in Xalapa, a site with acid soils, but not in LaBalsa which has alkaline soils. Furthermore, the best inoculant strain on A. pennatula in Xalapa was isolated from the very field where the inoculation trial was run. The data suggest that while the inoculation response of leguminous trees may vary with site or species, the benefits possible from the establishment of a highly effective tripartite symbiosis warrant including Rhizobium and VA mycorrhizae inoculation trials in all tree legume programs.