Soil microbial responses
Soil microbial OTU richness was not associated with invasion in B. arvensis gradients and only marginally associated with invasion inB. tectorum gradients, where microbe richness slightly decreased with increasing invasion (Figure 1c, Appendix S1: Table S1). Likewise, microbial community (Figure 2c, Appendix S1: Table S2) and functional (Figure 3c, Appendix S1: Table S3) composition differed with invasion inB. tectorum gradients only. At the functional group scale, two soil microbial functional groups (oxygenic photoautotrophy and photosynthetic cyanobacteria) were marginally negatively correlated withB. arvensis invasion in Montana, while 9 (2 positive, 7 negative) and 22 (all negative) microbial functional groups were marginally or significantly correlated with B. arvensis and B. tectoruminvasion in Wyoming, respectively (Appendix S1: Figure S3c, Table S4). For both bromes in Wyoming, microbial functional groups engaged in some form of phototrophy (phototrophs, photoheterotrophs, etc.) displayed the strongest negative correlations with invasion (Appendix S1: Figure S3c, Table S4). For B. tectorum , microbial functional groups associated with nitrogen and methanol cycling were also strongly negatively associated with invasion (Appendix S1: Figure S3c, Table S4).