Background and Aims

Divergences in resource-acquisition strategies driven by root functional traits between grasses and forbs govern their coexistence patterns in grassland communities. Despite root microbiomes having been revealed as an integral part of root functionality, it remains unclear how plant functional groups, along with their specific root traits, regulate the fitness and assembly of their root microbiomes.

Methods

We collected root samples from five grass and five forb perennial species in a typical natural grassland and measured their root traits. We also characterized the differences in niche breadths of root bacteria with Levins’ index, and calculated the nearest taxon index (NTI) to reveal the phylogenetic clustering/dispersion patterns of root bacterial communities.

Results

Grass root bacteria exhibited broader niche breadths than those of forbs. Additionally, the variation gradient in root traits between grasses and forbs significantly influenced bacterial niche breadth, which increased with higher specific root length and lower root tissue density/root diameter. The grass root bacterial communities also exhibited a higher NTI, indicating both stronger selective pressures exerted by grasses on bacterial community assembly and enhanced phylogenetic clustering, suggesting more similar ecological preferences among bacterial taxa in grass roots. Furthermore, stronger selective forces on root bacterial taxa led to higher bacterial niche breadth.

Conclusion

Compared to forbs, grasses, which are characterized by more resource-acquisitive traits, host bacteria with higher adaptability to their roots, thereby enhancing the grasses’ adaptive capacity. Our results provide further evidence for the positive feedback loops between plants and their associated microorganisms.