Structure and activities of ectomycorrhizal and microbial communities in the rhizosphere of Fagus sylvatica under ozone and pathogen stress in a lysimeter study

The aim was to study the influence of abiotic (elevated ozone) or biotic stress (Phytophthora citricola) or their combination on soil biological components and processes in the rhizosphere of young beech trees. Ectomycorrhizal and overall microbial community composition was studied at two soil depths in a lysimeter experiment with 7 year old trees of Fagus sylvatica. As a functional parameter, potential enzyme activities were measured in mycorrhizosphere soil and on excised mycorrhizal tips. The degree of mycorrhization, structure and potential enzymatic activities of mycorrhizal communities were only slightly influenced by treatments. Soil enzyme activities were depressed under elevated ozone and stimulated by P. citricola under ambient but not under elevated ozone. Overall microbial community composition (PLFA) and ectomycorrhizal diversity changed with depth. PLFA analyses not only suggested a reaction of the microbial community to elevated ozone but also indicated an increase in plant stress related components. No influence of the biotic stress on ectomycorrhizal or overall microbial community structure was detected. Changes in the mycorrhizosphere community structure and function due to ozone may be explained by the quality of plant derived carbon.