PSF and grassland invasion by Bromus
Bromus tended to experience positive growth responses to soil
inocula, especially those from Bromus -invaded plots (Table 1).
This could appear as evidence for enemy release, whereby the invasiveBromus is escaping pathogens that drive negative PSF on native
species (e.g., Klironomos, 2002). However, the lack of pathogenic OTUs
specifically detrimental to Koeleria (Fig. 2) fails to support
this hypothesis. Positive PSF developed by Bromus in these
grasslands may rather arise from its capacity to establish beneficial
interactions with non-symbiotic, nutrient-cycling microorganisms. This
deserves further consideration in invasion ecology, with many study
providing evidence for exotic species experiencing less negative PSF
(Klironomos et al. , 2002; Reinhart et al. , 2003; Aldorfovaet al. , 2020), but few actually demonstrating the implications
for soil-borne enemies in this pattern (e.g., Beckstead & Parker,
2003). Exotic species could be more versatile in developing positive
interactions with foreign soil microbiota. Our results show (Fig. 2)
that non-pathogenic and non-symbiotic microorganisms deserve more
attention that they have received in prior research on PSF in the
context of plant invasion (e.g., Vogelsang & Bever, 2009; Zhang et al.,
2010).