Are PSF-driving microorganisms strongly tied to vegetation structure?
A major, and often taken for granted, assumption of PSF theory is that soil microorganisms will respond to shifts in plant community structure. This is a necessary prerequisite for plant and soil microbial communities to oscillate and eventually converge to a stable equilibrium (Bever, 1999). While many studies have found soil organisms to be responsive to plant community structure (e.g., Eom et al. , 2000; Bezemer et al. , 2010; Chagnon et al. , 2020), many others have found that soil is rather the dominant filter (e.g., Dumbrellet al. , 2010). Here, we found that plant community structure and soil properties jointly determined microbial community structure (Fig. 3). Interestingly, we found that PSF-causing OTUs were not more strongly tied to the plant community than to the soil. This suggests that if soil properties are sufficiently heterogeneous at local scales, it could reduce the importance of PSF as drivers of plant and microbial community assembly. In this context, the soil microbiome could be more tied to soil properties and less responsive to plant community structure, thereby disrupting the feedback dynamics between plants and soil microorganisms.