COLLECTION OF ROOT AND SOIL SAMPLES
The mixtures of roots and rhizosphere soils coming from non-dune soils were collected from a depth of ca. 5-30 cm. Soil-root samples from dunes were usually taken from deeper zones of the soils; it depended on the depth of the occurrence of roots. The tools used to collect root-soil mixtures were either a small garden shovel (used in most cases) or a metal soil sample tube with graduations every two centimeters (used in ecological investigations). The latter tool enabled to precisely sample the root-soil material considering its amount and the place of origin. The root-soil mixtures collected were subsequently placed in plastic bags and transferred to the laboratory. In the laboratory, they were air dried and stored in a refrigerator at 4oC until processing.