Resource availability modulates above- and below-ground competitive interactions between genotypes of a dominant C4 grass



  1. The well-described pattern of a few common and many rare species in plant communities (dominance-diversity curves) also has been documented within populations of dominant plant species. Understanding how these common genotypes coexist has implications for how genotype richness of a dominant species may impact community and ecosystem processes. Some studies have shown that increased genotype richness of a dominant species leads to an increase in above-ground productivity, suggesting niche complementarity between genotypes. However, mechanistic understanding of how genotypes may complement one another is lacking.
  2. We conducted a pairwise competition experiment between four common and naturally co-occurring genotypes of a dominant C4 grass species, Andropogon gerardii, in tallgrass prairie of the central United States. The genotypes were grown under both intra- and intergenotypic competition with different combinations of resources (low and high light, water, and nitrogen) in the greenhouse.
  3. We determined that there were above- and below-ground phenotypic differences between genotypes which results in altered competitive interactions depending on resource conditions. Different genotypes were competitively dominant under low- and high-light conditions and low and high N and water availability. Moreover, relative yield total values (RYT) for each genotype pairwise combination indicated that all four genotypes make demands on different resources, providing evidence for niche complementarity.

  4. Finally, we found that differential success in resource acquisition, biomass accumulation, and subsequent competitive ability translated to variation in vegetative reproductive success of the genotypes, which has implications for the population dynamics of this primarily asexually reproducing perennial grass.

  5. Our results suggest that naturally co-occurring genotypes coexist because they are competitively dominant under different environmental conditions, providing insight into how genetic diversity within dominant plant species is maintained and may potentially affect important ecosystem processes.