Results
Each soil inoculum contained ~ 125 prokaryotic and ~150 fungal OTUs (Fig. S5), for a regional total of 887 and 1534 OTUs, respectively. These inocula tended to generate neutral to negative growth responses for Koeleria , but positive responses for Bromus , with a lack of correlation between the PSF experienced by the two species (Fig. 1, Spearman’s ρ = 0.042,P = 0.53). Bromus and Koeleria were also influenced by different OTUs as evidenced by our indicator species analysis (Fig. 2). However, no microbial OTU was found to influence Koeleriaonly. This could indicate a lower sensitivity of Koeleria to the soil microbiome, which is in line with its plant growth responses (t -score values) spanning less units than for Bromus(Koeleria [-3,1] except for an outlier at +3 ; Bromus[-4,4]) (Fig. 1). We note a complete absence of OTUs influencing positively one species but negatively the other. Such combinations of ecological outcomes are the ones expected to drive the strongest PSF, yet are absent from a metacommunity of over 2400 microbial OTUs.