Contrasting responses of the bacterial communities in ectomycorrhizal roots and rhizosphere soils to defoliation or winter hardening

Abstract

We examined the effects of photosynthetic activity of the host tree on the bacterial communities in ectomycorrhizal (ECM) roots and in rhizosphere soil. The seedlings of two host tree species, birch (Betula pendula) and pine (Pinus sylvestris), were subjected to winter hardening treatments for inducing total (birch) or partial (pine) restriction of the photosynthesis. Additionally, physical defoliation was performed to prevent both tree species from photosynthetic activity entirely. The bacterial communities were analyzed by RT-PCR of 16S rRNA followed by DGGE. After winter hardening, the bacterial communities in ECM roots of both host species shifted considerably while no consistent change was observed after physical defoliation. In contrast, no significant separation of the communities in rhizosphere soil was observed after winter hardening in either of the host species although the communities were significantly altered after physical defoliation compared to those of non-defoliated control in both tree species. It is therefore interesting and curious that the bacteria communities of ectomycorrhizal roots respond differently than the rhizosphere soil, to both defoliation and winter-hardening