AUTHOR=Wagner Katharina , Krause Katrin , Gallegos-Monterrosa Ramses , Sammer Dominik , Kovács Ákos T. , Kothe Erika 

TITLE=The Ectomycorrhizospheric Habitat of Norway Spruce and Tricholoma vaccinum: Promotion of Plant Growth and Fitness by a Rich Microorganismic Community

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.00307

DOI=10.3389/fmicb.2019.00307

ISSN=1664-302X

ABSTRACT=<p>The contribution of the mycorrhizospheric microbes in a stand of ectomycorrhizal Norway spruce (<italic>Picea abies</italic>) featuring mycorrhiza with the basidiomycete <italic>Tricholoma vaccinum</italic> was addressed by microbiome analysis and <italic>in vitro</italic> reconstruction of microbial as well as plant-microbe interactions. The protective role of the mycorrhizal fungus with respect to pathogen attack could be validated against <italic>Botrytis cinerea</italic> and <italic>Heterobasidion annosum</italic> in co-cultures revealing reduced pathogen growth, higher survival rate of the spruce trees and reduced symptoms on needles upon symbiosis with <italic>T. vaccinum.</italic> The community structure was shown to yield a high diversity in ECM forming basidiomycetes of <italic>Thelephorales</italic> and <italic>Agaricales</italic> associated with a rich bacterial diversity dominated by <italic>Rhizobiales</italic> with the most abundant <italic>Nitrobacter winogradski</italic> (3.9%). Isolated bacteria were then used to address plant growth promoting abilities, which included production of the phytohormone indole-3-acetic acid (performed by 74% of the bacterial isolates), siderophores (22%), and phosphate mobilization (23%). Among the isolates, mycorrhiza helper bacteria (MHB) were identified, with <italic>Bacillus cereus</italic> MRZ-1 inducing hyperbranching in <italic>T. vaccinum</italic>, supporting tree germination, shoot elongation, and root formation as well as higher mycorrhization rates. Thus, a huge pool of potential MHB and fungal community with widely distributed auxin-production potential extended the ability of <italic>T. vaccinum</italic> to form ectomycorrhiza. The forest community profited from the mycorrhizal fungus <italic>T. vaccinum</italic>, with spruce survival enhanced by 33% in microcosms using soil from the native habitat. A higher fungal abundance and diversity in cases where the tree had died during the experiment, showing that decomposition of plant litter from a dead tree supported a different community. <italic>T. vaccinum</italic> thus actively structured the community of microorganisms in its habitat.</p>