DNA concentration has been recently used as a proxy of surface soil biomass55,56. In the Scotland data set, this variable is strongly related to the glucose substrate-induced respiration (Spearman’s ρ=0.70; P<0.001), a common proxy of soil microbial biomass57.
I find it strange that, here, diversity is used as a predictor of microbial abundance. I think these are likely to be well correlated and the causal link is more likely to be inversed.