The role of fire on the relationships between genotypic diversity of the dominant species, species diversity, and productivity in the tallgrass prairie

Background/Question/Methods

Fire in the tallgrass prairie is a strong selective filter that impacts diversity, in part by altering environmental resources such as light, nitrogen, and water. The objective of this study is to determine the impact of a broad range of fire frequencies (1, 2, 4, 20 year burn) on the relationships between genotypic diversity, species diversity, and productivity. Increased burn frequency reduces community species diversity while increasing dominance of grasses. The same mechanisms that allow fire to shape community diversity could be occurring at the population level within the dominant grass species. There are three hypothesized outcomes from this study: 1) a negative relationship between genotype diversity and fire frequency, 2) a positive relationship between genotype diversity and fire frequency, or 3) a humped shaped relationship between genotype diversity and fire frequency (i.e., intermediate disturbance hypothesis). During the 2009 growing season, we collected samples from five 1-m2 plots arrayed 10 m apart on each of two permanent transects in each burn treatment maintained since 1984 at Konza Prairie LTER. In one transect, we sampled nine equidistant tillers in each plot, and the second, we sampled 23 equidistant tillers for a finer scale sampling.

Results/Conclusions

In addition to measuring genotype richness, we used pairwise Dice dissimilarity to assess relatedness as a measure of genotypic diversity. Overall, we found a negative relationship between genotype richness and burn treatment (, r² = -0.4464 p = 0.0634) with 20 year burn having the least number of genotypes. However, the 4 year burn frequency had a significantly lower genotypic diversity (relatedness) (p < 0.001) when compared to all other fire frequencies. Relationships between genotypic diversity, species diversity, and productivity differed between burn treatments. Genotype richness was negatively related to productivity (p = 0.0168, r² = -0.94169) and positively related to species diversity (p = 0.0397, r² = 0.89594) with annual burning. Genotypic diversity was positively related to species diversity with burning every 2 years (p =0.083, r² = 0.82852) and negatively related in a 4 year burn (p = 0.0952, r² = -0.90481). There were no significant relationships in 20 year burn. Overall, we see evidence of decrease genotype richness with less frequent fire due to decreased genotype richness within the dominant species. However, genetic relatedness was the lowest in the intermediate burn treatment (4 years). Finally, patterns of diversity and productivity differed between the burn treatments.