Nutrient use preferences among soil Streptomyces suggest greater resource competition in monoculture than polyculture plant communities

Background an aims: Nutrient use overlap among sympatric Streptomyces populations is correlated with pathogen inhibitory capacity, yet there is little information on either the factors that influence nutrient use overlap among coexisting populations or the diversity of nutrient use among soil Streptomyces. Methods: We examined the effects of plant host and plant species richness on nutrient use of Streptomyces isolated from the rhizosphere of Andropogon gerardii (Ag) and Lespedeza capitata (Lc) growing in communities of 1 (monoculture) or 16 (polyculture) plant species. Growth on 95 carbon sources was assessed over 5d. Results: Cumulative growth was significantly greater for polyculture vs. monoculture isolates, and for Lc vs. Ag isolates. Isolates from monocultures, but not polycultures, exhibited a drop in growth rates between 24 h and 72 h post-inoculation, suggesting resource allocation to non-growth functions. Isolates from high-carbon (polyculture) or high-nitrogen (Lc) soils had larger niche widths than isolates from low-C (monocultures) or low-N (Ag) soils. Sympatric isolates from polycultures were significantly more differentiated from one another in preferred nutrients for growth than sympatric isolates from monocultures. Conclusions: These results suggest that Streptomyces populations respond to selection imposed by plant host and plant community richness and that populations from polyculture but not from monoculture, mediate resource competition via niche differentiation.