Plants and the soil microorganisms near their roots live interdependent lives. Both groups respond to changes in resource availability and soil conditions, and their impacts on each other can create plant-soil feedbacks that alter plant communities and ecosystem function. Yet, the enormous diversity of soil microbes and diversity in plant species’ litter and root exudates make it challenging to generalize how plant-microbe associations vary across plant species, and consequently, how plants and soils respond to environmental change. To address these problems, we conducted a greenhouse experiment with seven grass species in the genus Poa and their native soils to examine how plant species influence rhizosphere fungi and bacteria. We applied a nitrogen (N) treatment to half the pots to assess the impact of this environmental change on plant-microbe associations. Using ITS and 16S marker gene sequencing, we determined the relative abundances of microbial taxa on plants’ roots, and then compared microbial composition among plant species and N treatments. We hypothesized that congeneric plant species exhibit unique, effects on rhizosphere communities, and that N addition enhances the unique effects of different plant species as opposed to disrupting the ability of plant species to promote unique community structure.
Results/Conclusions
We found that plant species fostered distinct fungal communities, providing some support for our first hypothesis. Bacteria populations were strongly altered by N addition, but overlapped considerably among plant species. As expected, N addition impacted fungal and bacteria community structure and plant growth. In support of our second hypothesis, individual plant species did indeed maintain unique effects on microbial composition in pots that received N. The differences in community structure due to plants and nitrogen together were not, however, related to the degree to which plant species increased their growth in the fertilized pots. This study increases our resolution on plant-microbe interactions, revealing that closely related plant species show unique impacts on microbial communities, and that the plant species effect is enhanced by resource addition. These results have implications for predicting plant-soil feedbacks. Since plant-microbe associations may remain strong with resource addition, this suggests that a microbial perspective may be important for predicting plant responses to N deposition.