Temporal and spacial dynamics of metabolically active bacteria associated with ectomycorrhizal roots of Betula pubescens

摘要

Bacteria, mycorrhizal fungi and their host plants are ubiquitous terrestrial associations but their interactions are poorly understood. To investigate the effects of seasonal change of host plant phenology on the bacterial communities in ectomycorrhizal (ECM) roots, bacterial communities in birch root tips with different ECM fungal species, those of non-mycorrhizal roots and those in bulk soil, were examined over a 15-month period, including two autumn seasons of 2008 and 2009, in field settings. Morphotyping and sequencing to identify the fungal species and RNA-based DGGE, cloning and sequencing were used to characterise the active bacterial communities. The most frequently observed fungus was Leccinum scabrum while other ECM fungi including Hebeloma velutipes, Russula versicolor and unidentified Cortinarius and Tomentella species were commonly found. ECM roots with L. scabrum hosted declining numbers of bacterial sequence types, observed as distinct bands on the DGGE profile, from spring to autumn in 2009. The numbers of sequence types associated with L. scabrum and non-mycorrhizal roots were reduced in autumn 2009 than in autumn 2008, but the numbers associated with other ECM roots and bulk soil were constant over the same period. Roots with L. scabrum harboured unique bacterial communities which were distinct from bulk soils, non-mycorrhizal roots and roots with other ECM fungi in 2008 but the differences were less clear in 2009. The results indicate that the metabolically active bacterial communities in ECM are influenced by fungal species, seasonal host plant phenology and show year to year variation.