Soil sampling and root analysis
Root sampling was conducted in each three transects of 30 m £ 1 m per study plot that were randomly placed in the 50 m £ 50 m plots. Each eight sampling locations per tran- sect were randomly chosen resulting in 24 coring locations per plot. Minimum distance between two sampling locations was 1 m in order to avoid mutual disturbance through cor- ing. Soil coring was conducted at each location (one sam- pling date in 2005 or 2006) in the soil proWle to 40 cm depth (including the organic layer) with a steel corer 3.5 cm in diameter. The cores were sliced into four sub-samples of 10 cm length each. The samples were stored in plastic bags at 5°C and processed within 6 weeks. For analyzing the Wne root mass (diameter ·2 mm), the samples were soaked in water and cleaned from soil residues using a sieve (mesh size 0.25 mm). Fine root fragments longer than 1 cm were collected by hand with a pair of tweezers, separated into live and dead fractions using a stereomicroscope and sorted by species. For separating live and dead root fractions, morpho- logical criteria such as root elasticity, the degree of cohesion of root stele and periderm, and the presence or absence of the stele were used (Persson 1978; Leuschner et al. 2001). For species identiWcation, a classiWcation system based on morphological attributes, such as surface structure and color of the periderm, ramiWcation pattern, and type of mycorrhi- zal infection was used. This identiWcation key is based on Wne root material of diVerent species extracted in the rhizo- sphere of isolated individuals where species identiWcation