Abstract
Tree root-associated microbiomes are shaped by geographic, soil physico-chemical, and host tree parameters. However, their respective impacts on microbiome variations in soils across larger spatial scales remain weakly studied. We out-planted saplings of oak clone DF159 (Quercus robur L.) as phytometer in four grassland field sites along a European North-South transect. After four years, we first compared the soil microbiomes of the tree root zone (RZ) and the tree root-free zone (RFZ). Then, we separately considered the total microbiomes of both zones, besides the microbiome with significant affinity to the RZ and compared their variability along the transect. Variations within the microbiome of the tree RFZ were shaped by geographic and soil physico-chemical changes, whereby bacteria responded more than fungi. Variations within both microbiomes of the tree RZ depended on the host tree and abiotic parameters. Based on perMANOVA and Mantel correlation tests, impacts of site specificities and geographic distance strongly decreased for the tree RZ affine microbiome. This pattern was more pronounced for fungi than bacteria. Shaping the microbiome of the soil zones in root proximity might be a mechanism mediating the acclimation of oaks to a wide range of environmental conditions across geographic regions.
Highlights
Soils harbor an immense biodiversity because they represent extremely heterogeneous and changing habitats both spatially and temporally, providing myriads of microniches, which enable habitat specialization or coexistence of species (Bardgett, 2002)
When cumulating the pure and combined impacts derived from interactions with other sources of variability, we found for the root zone (RZ) total microbiomes a descending order of magnitude: geographic (68.6% of bacterial, 51.9% of fungal variations); soil physico-chemical (66.5% of bacterial, 44.6% of fungal variations); oak tree parameters (60.7% of bacterial, 38.4% of fungal variations)
For the RZ affine microbiomes, we observed no pure impact of the tested sources of the variability for the bacteria, while for the fungi, we had 32.3% purely explained by the tree parameters and 14.8% individually explained by soil physico-chemical and geographic parameters
Summary
Soils harbor an immense biodiversity because they represent extremely heterogeneous and changing habitats both spatially and temporally, providing myriads of microniches, which enable habitat specialization or coexistence of species (Bardgett, 2002). Soil microbial communities vary with land-use types (Schöps et al, 2018; Xue et al, 2018; Plassart et al, 2019) and vegetation (Carney and Matson, 2006) Such biotic filtering is strongly linked to the fact that plant roots establish close associations with specific groups of soil microorganisms, especially those with plant-beneficial properties (Hartman and Tringe, 2019), for instance, the ones involved in plant nutrition as well as resistance to abiotic and biotic stresses (Lugtenberg et al, 2002; Vandenkoornhuyse et al, 2015). This should induce changes in the tree root associated microbial communities
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