Does functional soil microbial diversity contribute to explain within-site plant β-diversity in an alpine grassland and a dehesa meadow in Spain?

Questions
Once effects of hydrological and chemical soil properties have been accounted for, does soil microbial diversity contribute to explain change in plant community structure (i.e. within-site β-diversity)? If so, at what spatial scale does microbial diversity operate?
Location
La Mina in Moscosa Farm, Salamanca, western Spain (dehesa community) and Laguna Larga in the Urbión Peaks, Soria, central-northern Spain (alpine grassland).
Methods
The abundance of vascular plant species, soil Gram-negative microbial functional types and soil chemical properties (pH, available P, extractable cations) were sampled at both sites, for which hydrological models were available. RDA was used to partition variation in plant community structure into hydrological, chemical and microbial components. Spatial filters, arranged in scalograms, were used to test for the spatial scales at which plant community structure changes.
Results
In the case of the dehesa the diversity of soil Gram-negative ...