Soil sampling There is extensive heterogeneity of microorganisms in ural environments, especia rate information on the diversity of diazotrophic bacteria, the method of soil sampling used is vital. Several recent reports have insisted that at least 4-6 plant samples are required to retrieve diazotroph-related genes from rhizosphere soils (6, 9, 19). We sampled the root systems of M malabathricum from three individual plants in each soil type. We also sam- pled a large number (>10) of root pieces (ca. 10 cm) from the entire root system of a plant, and then mixed them. Thus, although the number of plants sampled was less than in other reports, the rhizosphere soil was sampled not from one root but from the root system, and then pooled. Thus we consider that DNA extracted from this pool represents DNA of the rhizosphere of the entire root system o M malabathricum