1. Dep. of Plant Ecology; Justus-Liebig-Univ. Giessen, Germany; Heinrich-Buff-Ring 26-32 D-35392 Giessen Germany
2. School of Biology and Environmental Science, Univ. College Dublin; Belfield Dublin Ireland
3. Dep. of Applied Microbiology; Justus-Liebig-Univ. Giessen; Heinrich-Buff-Ring 26-32 D-35392 Giessen Germany